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# The A Level Biologist - Your Hub

## Sitemaps

- [XML Sitemap](https://thealevelbiologist.co.uk/sitemap.xml): Contains all public & indexable URLs for this website.

## Posts

- [How to Research Anything in Life Science](https://thealevelbiologist.co.uk/how-to-research-anything-in-life-science/) - Make no mistake, this content is for YOU. Yes, you. Do you think biology is “too academic” for you? Is it all too far gone and confusing? Well, I’ve tried to boil it all down to 13 minutes. There, how to research anything in life science. If you’re alive – then you do care, believe me ?
- [Working as an NHS Dentist](https://thealevelbiologist.co.uk/working-as-an-nhs-dentist/) - She’s my mother, but she’s also a dentist. This one’s for all you trapped in the spinning wheel of “breaking through” to become a dentist, and, of course, everyone else burning to find out exactly how much she’s ever made in one month.
- [How X_Y Chromosomes Actually Work](https://thealevelbiologist.co.uk/how-x-y-chromosomes-actually-work/) - Everyone gets taught at some point about sex determination in humans, and I say specifically humans, because there are many different types of sex determination, such as the ZW system, where the males are the simpler genetic default, and the females require that extra something to develop, as with the Y chromosome for males in the XY system.
- [Indefinite Health with Dr. Aubrey de Grey](https://thealevelbiologist.co.uk/indefinite-health-with-dr-aubrey-de-grey/) - As we enter the golden age of life science we should not just keep getting sick and dying. Too much to ask for?
- [Intimate Bio Design with Giulia Tomasello](https://thealevelbiologist.co.uk/intimate-bio-design-with-giulia-tomasello/) - Award-winning interaction designer Giulia Tomasello brings DIY biohacking to everyday life in order to inspire and empower us to think about, and boost, genital health. Oh, and casually destroys taboos while she's at it.
- [Scottish Science Secret Agent Ian Inkster](https://thealevelbiologist.co.uk/scottish-science-secret-agent-ian-inkster/) - Rockstar writer Ian Inkster entered the world of science through the back door, set up backstage and decided to stay there. He shaped the language of one of the hottest fields in biomedicine - rejuvenation biotechnology - by freelancing for the biotech rockstars on the stage.
- [Science Sing-along with John Hinton](https://thealevelbiologist.co.uk/science-sing-along-with-john-hinton/) - Multi-talented artist John Hinton has written amazing songs about science, animals, plants and more! How much you learn is up to you, but one thing is sure: you will be tapping your foot to death.
- [Cambridge Chat with Saba Shirvani](https://thealevelbiologist.co.uk/cambridge-chat-with-saba-shirvani/) - PhD student Saba shares her work in groundbreaking medical imaging research funded by the EU Horizon 2020 project at the University of Cambridge. We also chat about how Cambridge is changing, Saba's educational background and multilingualism, and whether Nikola Tesla would approve of the present day company bearing his name.
- [Season 2 Announcement](https://thealevelbiologist.co.uk/season-2-announcement/) - All the stats of Season 1, planning Season 2 and thanks where thanks are due.
- [Corona Special](https://thealevelbiologist.co.uk/corona-special/) - Questions, thoughts and even a poem for coronavirus.
- [The Anatomy of Getting into Science](https://thealevelbiologist.co.uk/the-anatomy-of-getting-into-science/) - With everything thrown up in the air, here is one story of exams, universities and personal drama shaping the journey of getting into science - something Arian just wasn't going to give up on.
- [Hindsight Is 2020](https://thealevelbiologist.co.uk/hindsight-is-2020/)
- [Lucie's Reef Relief](https://thealevelbiologist.co.uk/lucies-reef-relief/)
- [Shelby's Venture Adventure](https://thealevelbiologist.co.uk/shelbys-venture-adventure/)
- [Hilary's Hilarious Science History](https://thealevelbiologist.co.uk/hilarys-hilarious-science-history/)
- [Life Science Consulting with Dr. Iris Batalha](https://thealevelbiologist.co.uk/life-science-consulting-with-dr-iris-batalha/)
- [Baby Brain, a Theory of Hormonal Regulation](https://thealevelbiologist.co.uk/baby-brain-a-theory-of-hormonal-regulation/)
- [Herbs to Fight PMS with Lauren & Matt](https://thealevelbiologist.co.uk/herbs-to-fight-pms-with-lauren-matt/)
- [Season 3 Announcement](https://thealevelbiologist.co.uk/season-3-announcement/)
- [PhD Premiere: AI & Mental Health with Dr. Kasia Kozdon](https://thealevelbiologist.co.uk/phd-premiere-ai-mental-health-with-dr-kasia-kozdon/)
- [How to Freelance Scientific Illustrate with Swedish Entrepreneur Dr. Daria Chrobok](https://thealevelbiologist.co.uk/how-to-freelance-scientific-illustrate-with-swedish-entrepreneur-dr-daria-chrobok/)
- [Dodging Uni to Help Students Study Better in London with Mohammad Awais](https://thealevelbiologist.co.uk/dodging-uni-to-help-students-study-better-in-london-with-mohammad-awais/)
- [The Exclusive Story of the NHS Dentist Who Risked Her Job to Secure Govt U-turn on Vaccine Mandate](https://thealevelbiologist.co.uk/the-exclusive-story-of-the-nhs-dentist-who-risked-her-job-to-secure-govt-u-turn-on-vaccine-mandate/)
- [The Mathematical Reason We Need So Many Sperm Cells](https://thealevelbiologist.co.uk/the-mathematical-reason-we-need-so-many-sperm-cells/)
- [Avatar: The Way of Water (Top 5 Biology Moments)](https://thealevelbiologist.co.uk/avatar-the-way-of-water-top-5-biology-moments/)
- [❤️ Putting the Life in Life Science](https://thealevelbiologist.co.uk/putting-the-life-in-life-science/) - Toby chats life, school, LadBaby videos and the NHS. Beyond the ins and outs of bleeding edge science lies life itself.

## Pages

- [Manage Profile](https://thealevelbiologist.co.uk/manage-profile/)
- [Manage Profile](https://thealevelbiologist.co.uk/manage-profile-2/)
- [Courses](https://thealevelbiologist.co.uk/courses/)
- [⭐ My Exam Board](https://thealevelbiologist.co.uk/my-exam-board/) - Keeping in touch with your exam board is useful. Here are the links to each of them.
- [Access TAB](https://thealevelbiologist.co.uk/access-tab/) - Come on in!
- [<strong>⛔ End-product inhibition</strong>](https://thealevelbiologist.co.uk/end-product-inhibition/) - In metabolic pathways, reaction rates can be determined by the relative concentration of substrates and products of a reaction or series of reactions. The substrate presence can drive the reactions to continue for as long as there is substrate available, or alternatively the reactions could continue for as long as the product is being removed, in order to maintain a constant level.
- [✍️ Revision Tips](https://thealevelbiologist.co.uk/revision-tips/) - Time-tested revision tips to help you organise your learning and hit your targets.
- [Season 3](https://thealevelbiologist.co.uk/season-3/) - The A Level Biology Podcasts opens up the gate to the best life science has to offer students and professionals alike. Listen to Season 2 now.
- [Sitemap](https://thealevelbiologist.co.uk/sitemap/) - TAB hosts hundreds of accurate, up to date and to-spec biology topics.
- [<strong>Environmental effects on genes</strong>](https://thealevelbiologist.co.uk/environmental-effects-on-genes/) - The foundation of the field of epigenetics (changes to gene expression that do not affect the genes themselves) was spurred by a series of studies dubbed the Norrbotten studies carried out in the remote and scarcely populated Norrbotten County in Sweden, near the Arctic circle.
- [<strong>Age-related vision loss</strong>](https://thealevelbiologist.co.uk/age-related-vision-loss/) - Age-related vision loss has multiple causes, the most prevalent of which are age-related macular degeneration (AMD) and glaucoma. Dry AMD occurs as cellular debris accumulates in the eye’s retinal pigment epithelial (RPE) cells, resulting in drusen deposits which damage the eye’s photoreceptor cells.
- [<strong>tRNA (Transfer RNA)</strong>](https://thealevelbiologist.co.uk/trna-transfer-rna/) - We know DNA is double-stranded and uses A, G, C and T bases, while mRNA is single-stranded and uses U instead of T. What about tRNA? Well, tRNA is a very different soup indeed.
- [<strong>Classical and operant conditioning</strong>](https://thealevelbiologist.co.uk/classical-and-operant-conditioning/) - Classical conditioning is the scenario of the dog salivating over food, then associating a bell ringing with the food and salivating thereafter at the sound of the bell only.
- [<strong>Affinity chromatography</strong>](https://thealevelbiologist.co.uk/affinity-chromatography/) - Affinity chromatography is the specific type of chromatography used in molecular biology research, as it enables the separation of given proteins from mixtures of bacterial cell lysates, buffers, etc. The concept of affinity is that some specific property of the target protein (size, presence of tags previously added for this purpose, chemical bonding including hydrogen bonding, disulfide bridges, ionic interactions, etc.) can be used to bind it to a stationary phase, while compounds that do not meet that criteria can be washed away.
- [<strong>Culturing media</strong>](https://thealevelbiologist.co.uk/culturing-media/) - Ok, so we have our glorious sample or microorganism or whatever that we’re about to grow. We grow it using special media, such as LB (lysogeny broth) for bacteria and YPD (yeast extract peptone dextrose) for yeast. These media contain basic nutrients like sugars and amino acids, and encourage microorganisms to thrive.
- [<strong>Movement and locomotion</strong>](https://thealevelbiologist.co.uk/movement-and-locomotion/) - The key characteristic of all animals is movement. They achieve this in many different ways. Microscopic organisms such as bacteria have a flagellum that they can wiggle to propel themselves. Spiders use passive movement whenever they glide downwards.
- [<strong>Visualising DNA with gel electrophoresis</strong>](https://thealevelbiologist.co.uk/visualising-dna-with-gel-electrophoresis/) - A common method of visualising differences is gel electrophoresis which involves loading small volumes of samples on a gel and running a current across it in order to separate the samples by size.
- [<strong>Research and referencing</strong>](https://thealevelbiologist.co.uk/research-and-referencing/) - Research relies on all the sources of information available. There are partially standardised media that specialise in certain areas of research, such as scientific papers (typical layout pictured) in journals, as well as textbooks, websites and other media that are useful at different stages of research, in different contexts and for different purposes.
- [<strong>Pollination and fertilisation</strong>](https://thealevelbiologist.co.uk/pollination-and-fertilisation/) - The pollen grain makes its way towards the embryo sac down the style of the ovary. The tube nucleus develops into a pollen tube which with the help of digestive enzymes that can break away through the style travels down towards the embryo sac.
- [<strong>Patterns of evolution</strong>](https://thealevelbiologist.co.uk/patterns-of-evolution/) - Evolution could happen evenly over time, or in bursts. The latter option is called punctuated equilibrium. Darwin’s perspective was that of evolution as a continuous process over time, but Eldridge and Gould proposed the theory of punctuated equilibrium.
- [<strong>Arthropoda (e.g. insect) body form</strong>](https://thealevelbiologist.co.uk/arthropoda-eg-insect-body-form/) - Arthropods including insects and arachnids are characterised by their jointed limbs and bilateral symmetry with a fixed number of metameric segments e.g. head, thorax, abdomen. They have both a mouth and an anus as part of a digestive tract with specialised regions (the caecae are appendages that contain gastric juice). The arthropod body form has enabled vast diversification of this animal group, including flight i.e. because the extra limbs could change without affecting the function carried out by the rest.
- [<strong>Annelida (e.g. earthworm) body form</strong>](https://thealevelbiologist.co.uk/annelida-eg-earthworm-body-form-and-feeding/) - Earthworms are also bilaterally symmetrical like flatworms, but instead of being flat, they are round in transverse section (widthways), as well as being segmented metamerically. Metameres are repeating sections in an organism that have the same structure, although may accomplish different functions based on their tissue distribution and specialisation.
- [<strong>Platyhelminthes (e.g. flatworm) body form</strong>](https://thealevelbiologist.co.uk/platyhelminthes-eg-flatworm-body-form-and-feeding/) - Flatworms like the liver fluke are bilaterally symmetrical and flattened dorso-ventrally. This means they are flat back (top) to front (bottom). Their bilateral symmetry means they are identical when split into two, lengthways in this case (unlike Cnidaria which are radially symmetrical). They have a single opening (mouth) to the gut. Its flat body tissues support its body structure, with no specialised skeletal system. Many flatworm species are parasitic.
- [<strong>⭐ Cnidaria (e.g. Hydra) body form</strong>](https://thealevelbiologist.co.uk/cnidaria-eg-hydra-body-form-and-feeding/) - Hydra and jellyfish are multicellular organisms that are radially symmetrical. This means they look identical when split at any point around a circle, looking downwards onto their body plan. They have very basic nervous systems and digestion, and the aqueous medium they reside in supports their bodies.
- [<strong>Angiosperm (e.g. flowering plant) form and adaptations</strong>](https://thealevelbiologist.co.uk/angiosperm-eg-flowering-plant-form-and-adaptations/) - Angiosperms go a step further from ferns in their adaptations to terrestrial life. They, of course, possess all the specialised structures like roots, stems, leaves, cuticles, stomata, xylems and tough seeds, which enable water conservation and dispersal of seeds for reproduction. In addition to all these adaptations shared with ferns, angiosperms (so-called because their seeds are enclosed e.g. in fruit) are capable of further adaptations to harsher environments, as well as adaptations that take advantage of other environmental niches.
- [<strong>Tracheophyta (e.g. fern) form</strong>](https://thealevelbiologist.co.uk/tracheophyta-eg-fern-form-and-life-cycle/) - Unlike mosses, ferns have differentiated parts i.e. true roots, stems and leaves. They are therefore better adapted to terrestrial life, and posses cuticles and stomata that enable better water retention. They also possess a vascular system with xylem vessels, etc. Structural support is given by both turgor in cells and the woody xylem vessels alongside other structures found in the vascular bundle.
- [<strong>Bryophyta (e.g. moss) form and adaptations</strong>](https://thealevelbiologist.co.uk/king-plantae/bryophyta-eg-moss-form-and-life-cycle/) - Mosses are simple plants with no differentiated parts i.e. leaves, stems, roots. They are multicellular and do not possess a cuticle or stomata except in the spore forming parts. Their features are adapted to moist conditions and vulnerable in dry conditions. Rhizoids are specialised for attachment to the soil. They do not penetrate deeply, so mosses only populate areas where water and ions are abundant higher in the soil.
- [<strong>Speciation (CCEA)</strong>](https://thealevelbiologist.co.uk/speciation/) - Given that the two habitats are different, the individuals in each population will adapt differently to counteract different selection pressures. Say for example the ants in the forest experience a warmer and more nutrient-rich surrounding compared to the emigrated ants on a nearby, although disconnected, beach.
- [<strong>Carbohydrates</strong>](https://thealevelbiologist.co.uk/carbohydrates/) - Starch, glycogen and cellulose are important examples of carbohydrates in biology. They have different basic units, function and structure. Here is table that compares them side by side.
- [<strong>Limiting factors (CCEA)</strong>](https://thealevelbiologist.co.uk/limiting-factors/) - The rate of photosynthesis can be monitored as a function of either CO2 uptake or O2 production. Since organisms that photosynthesise (such as plants) also undergo respiration (to have usable energy from the food they just made through photosynthesis), the relationship between the amount of photosynthesis and the amount of respiration that takes place at any time can be analysed.
- [<strong>Overview of photosynthesis</strong>](https://thealevelbiologist.co.uk/overview/) - H2O + CO2 + energy –> C6H12O6 + O2 …where water, carbon dioxide and energy are the starting materials, and glucose and oxygen the products. Here, glucose is the key product because it is the complex organic molecule made from simple inorganic reactants. The “energy”, as you may have noticed, is where the light comes in.
- [<strong>Forelimb muscle action and the role of tendons</strong>](https://thealevelbiologist.co.uk/forelimb-muscle-action-and-the-role-of-tendons/) - Antagonistic muscle action refers to pairs of opposite muscles working to create movement in opposite directions. Examples include the bicep-tricep pair in arms, and the quadricep-hamstring pair in legs. Confusingly (?!), the term forelimb is used to refer to any limb (leg, arm) in terrestrial vertebrates. Only one muscle in the antagonistic pair can contract at a given time. The contraction causes either flexion i.e. bending of the limb, or extension i.e. straightening of the limb.
- [<strong>Synovial joint structure</strong>](https://thealevelbiologist.co.uk/synovial-joint-structure/) - Synovial joints are those joints which have a gap between bones, rather than direct joining. If a joint isn’t synovial it is either fibrous (joined by dense connective tissue rich in collagen) or cartilaginous (joined by cartilage). The bones may be held together by ligaments, beyond which the joint capsule with its protective fluid secreted by the synovial membrane lies. The synovial membrane and synovial fluid act to lubricate the joint. The fluid contains nutrients, and can act as a shock absorbent.
- [<strong>Joints as levers</strong>](https://thealevelbiologist.co.uk/joints-as-levers/) - A lever in physical terms is an axis that moves a load about a fixed point. Joints, therefore, can be seen to act in levers as the fixed point. The axis/lever is the bone, while the load can be a body part or another object. The fixed point or joint in this case is termed a fulcrum. The other two key components in the lever are the weight or resistance and the effort.
- [<strong>Osteoarthritis and rheumatoid arthritis</strong>](https://thealevelbiologist.co.uk/osteoarthritis-and-rheumatoid-arthritis/) - The most common inflammation of the joints is osteoarthritis. It causes pain and swelling, and occurs as a result of small wear and tear of the joints over time that does not get repaired adequately. It often occurs in the knees, hips, neck, back and fingers. Risk factors include old age, injury, family history and obesity. Treatment for osteoarthritis includes painkillers, steroid injections and surgery depending on severity. Lifestyle management treatments include weight loss if necessary, regular exercise, wearing appropriate shoes and employing special devices to minimise the stress experienced by joints.
- [<strong>Joint types</strong>](https://thealevelbiologist.co.uk/joint-types/) - nlike cartilage and bones, joints are more of an abstract concept referring to the location between two bones, more than a specific type of tissue. They can be fixed with no movement at all e.g. skull bones, or lubricated and enabling frictionless movement e.g. hip joints. Types of joint are classified based on the type of movement they provide, as well as the structure of the bones they join. Hence, there are immovable/fused joints. They speak for themselves, and are represented by the skull, teeth and calf bones.
- [<strong>⚙️ Skeleton function</strong>](https://thealevelbiologist.co.uk/skeleton-function/) - The skeleton is made of robust bones containing calcium and bone marrow. Hence, its function is not just the support of the body’s other tissues and organs, but also the production of red blood cells and storage of calcium for the body. Physical functions of the skeleton include protection of organs such as the skull protecting the soft brain tissue, movement by the limbs and the vertebrae, and support of organs such as the rib cage supporting the lungs. Many of these functions work together with other systems such as muscles and nerves to generate movement and support.
- [<strong>Vertebrae and deformities</strong>](https://thealevelbiologist.co.uk/vertebrae-and-deformities/) - The vertebral column is what classifies all vertebrates as such, and acts to support the skeleton as part of the axial skeleton further including the rib cage and the skull. It protects the spinal cord contained within, which is one part of the central nervous system, carrying nerves to the whole body. As the name suggests, the column is composed of 33 vertebrae (in humans), which are the individual bones that line the column from top to bottom. The top 24 vertebrae are spaced by intervertebral discs made of fibrous cartilage, while the bottom 9 are fused e.g. the tailbone.
- [<strong>The skeleton and fractures</strong>](https://thealevelbiologist.co.uk/option-b-human-musculoskeletal/the-skeleton-and-fractures/) - The skeleton is the foundation of the anatomy of the body in humans. As we walk upright (most of the time!), the skeleton is split into the axial skeleton, which follows a vertical alignment of the main parts, and the appendicular skeleton which is supported through the axial skeleton. The axial skeleton includes the skull, rib cage and vertebrae, while the appendicular skeleton includes the bones that are based on them: the pectoral girdles, pelvis and limbs.
- [<strong>Muscle contraction fuels and conditions</strong>](https://thealevelbiologist.co.uk/muscle-contraction-fuels-and-conditions/) - Glycogen stored in muscle is the next port of call for energy during muscle contraction, as it can be broken down into glucose. In the absence of sugar-based energy, cortisol is released which stimulates protein breakdown as another source of energy. There are two main kinds of muscle fibre: slow twitch and fast twitch. Hmm, I do wonder what…
- [<strong>Sliding filament theory</strong>](https://thealevelbiologist.co.uk/sliding-filament-theory/) - This is a really good diagram for understanding the basic principle of actin (thin filaments) sliding over the myosin (thick filaments) to shorten the sarcomere and achieve contraction. If you understand this, you won’t be shocked by the inevitable trippy questions that examiners will hurl at you in the exam about fancy H/I/A bands/lines/zones. These randomly named lines/zones/bits/pieces are totally arbitrary. If you must know, the A band and I band referring to the length covered by myosin and actin respectively were established as a result of how they appear under a microscope.
- [<strong>Skeletal muscle</strong>](https://thealevelbiologist.co.uk/skeletal-muscle/) - The muscle is attached to the bone (spot the nice bone marrow) by the tendon. Muscle cells have a plasma membrane and cytoplasm much like any other cells, but each has a special name. How do muscles contract? I mean what is the deal with Z line, A band, I band…?!
- [<strong>Bone disease</strong>](https://thealevelbiologist.co.uk/rickets-and-osteomalacia/) - Rickets is a bone softness conditions affecting children, often following from malnutrition, and causing bone fractures and other symptoms. It is one of the most prevalent childhood diseases in developed areas. The cause is insufficient calcium, vitamin D or phosphorus, sometimes passed on during pregnancy as the foetus develops. Symptoms are bone fragility and deformities such as bowed legs in toddlers and windswept knees in children, as well as dental, pelvic and spinal deformities and problems.
- [<strong>Bone components and their function</strong>](https://thealevelbiologist.co.uk/bone-components-and-their-function/) - Bone is 70% inorganic mineral (such as calcium- and phosphate-containing hydroxyapatite) and 30% organic i.e. collagen. The inorganic component gives it its rigidity and strength, while the organic component gives it enough flexibility to prevent shattering. Bones have special cells that build the bone matrix while at the same time dissolve it. The balance of these opposing actions determine bone volume. The bone-building cells are osteoblasts while the bone-dissolving cells are osteoclasts.
- [<strong>Structure of cartilage</strong>](https://thealevelbiologist.co.uk/structure-of-cartilage/) - Cartilage is a type of smooth, elastic tissue that provides structural support to the body e.g. joints, between bones, ears, nose, trachea, ribs and others. It consists of special cells called chondrocytes whose job it is to produce a large amount of extracellular matrix, the material between cells, which gives cartilage its physical properties. Primarily, these components are collagen and proteolgycans, both proteins. Depending on location, cartilage can have different ratios of collagen to proteoglycans. This forms three categories of cartilage: hyaline cartilage, yellow elastic cartilage and white fibrous cartilage.
- [<strong>Aerobic and anaerobic respiration</strong>](https://thealevelbiologist.co.uk/aerobic-and-anaerobic-respiration/) - Of course not all organisms obtain their respiration substrate (e.g. glucose/food) by making it themselves as plants do, yet all carry out respiration. Don’t make the mistake of associating plants with photosynthesis, and non-plants with respiration. Aerobic respiration, as opposed to anaerobic respiration, occurs in the presence of oxygen, accounts for most respiration that takes place, and produced up to 15 times more ATP molecules.
- [<strong>Vaccination</strong>](https://thealevelbiologist.co.uk/vaccination/) - Our natural immunity does not cover certain pathogens such as the flu virus. Vaccination attempts to induce artificial immunity which is an add-on to our natural immunity, by adding an artificially triggered response specific to a new pathogen that we did not have innately. In the case of rabies, a vaccine is given containing antibodies in order to act as an emergency, passive treatment. Normally, the rabies vaccine would be given preventively to avoid getting the disease, but if someone is likely to have already got infected without prior vaccination, the administration of ready antibodies into their blood can help tackle the illness in its tracks.
- [<strong>Immune System (WJEC)</strong>](https://thealevelbiologist.co.uk/immune-system/) - The specific immune response is split into humoral immunity and cell-mediated immunity. Humoral is to do with the blood and antibodies. Distinguishing between an antigen and an antibody is very important. Antigen = protein or carbohydrate foreign (not normally present) to a host’s organism. Antibody = protein made as a response to detecting an antigen which binds to the antigen and prevents the pathogen from…
- [<strong>Virus pathogenicity and mode of reproduction</strong>](https://thealevelbiologist.co.uk/virus-pathogenicity-and-mode-of-reproduction/) - Both DNA and RNA viruses make use of their host’s transcription and translation machinery such as ribosomes and enzymes to enable protein synthesis. Retroviruses on the other hand bring their own reverse transcriptase enzyme to enable the production of DNA using their RNA template once inside the host cell. Once the RNA is reverse transcribed into DNA (DNA->RNA is transcription, hence RNA->DNA is reverse transcription), the normal protein synthesis pathway…
- [<strong>Malaria</strong>](https://thealevelbiologist.co.uk/malaria/) - High rates of transmission from mosquitoes to humans and from humans to mosquitoes (as you remember, the gametophytes of the Plasmodium parasite fuse inside the mosquito to create sporozoites; these are transmitted to humans and undergo further development to produce gametophytes again, which get transmitted back to mosquitoes). Malaria is transmitted via a vector which carries it without being affected, before passing it onto the final host of the parasite. In this case it is carried by the mosquito which transfers it via its bite in saliva.
- [<strong>Influenza</strong>](https://thealevelbiologist.co.uk/influenza/) - The mechanism of infection of influenza consists of its outer hemagglutinin protein being cleaved by proteases present in human cells. These are found in the throat and lungs, so other tissues don’t get infected as a result. More virulent strains like the bird flu strain H5N1 on the other hand, can have their hemagglutinin cleaved by other types of proteases, hence enable their spread to other parts of the body.
- [<strong>Smallpox</strong>](https://thealevelbiologist.co.uk/smallpox/) - It’s thought that the virus reached humans tens of thousands of years ago, through an African rodent. Its mode of transmission is mainly airborne via infected patient droplets, and potentially via other intimate contact items such as bedding. The virus spreads through the respiratory system as it incubates, at which point it travels from cell to cell, relatively slowly. Initial symptoms include fever, fatigue, nausea, and other general flu-like symptoms.
- [<strong>Tuberculosis</strong>](https://thealevelbiologist.co.uk/tuberculosis/) - When bacteria reach the alveoli, the immune system reacts by surrounding them with white blood cells, which results in the formation of scar tissue. The shortness of breath symptom is caused by less oxygen reaching the circulatory system due to a decreased surface area for diffusion in the lungs, as many alveoli are damaged. Treatment involves a course of antibiotics which can be lengthy, resulting in many patients stopping at the first signs of amelioration of their symptoms. This causes resistance in the bacteria, which come back to cause disease. Moreover, antibiotic-resistant strains have emerged.
- [<strong>Genomics, gene therapy and stem cells</strong>](https://thealevelbiologist.co.uk/genomics-gene-therapy-and-stem-cells/) - Genomic medicine started in the areas of oncology, pharmacology, rare and undiagnosed diseases and infectious disease. Risk prediction is employed by studying associations between certain diseases and the presence of specific genes preferentially in that patient population. Sometimes, especially for rare disease that tend to have a single genetic root, it’s possible to know the mechanism by which that mutation causes a disease. However, other times this isn’t elucidated and all we can work with is the knowledge that, for whatever reason as of yet unknown, the association stands.
- [<strong>PCR, gel electrophoresis and GMOs</strong>](https://thealevelbiologist.co.uk/pcr-gel-electrophoresis-and-gmos/) - Essentially the DNA is denatured so the 2 strands break apart, short complementary bits called primers attach to the strands, the enzyme DNA polymerase binds to the primers and initiates the assembly of a new DNA strand, and finally the process is repeated many times over in a chain reaction. This is the polymerase chain reaction, PCR. Soon enough, the few bits of DNA become thousands, and hundreds of thousands, and millions…
- [<strong>Human Genome Project and its implications</strong>](https://thealevelbiologist.co.uk/human-genome-project-and-its-implications/) - I got some of my DNA screened for several select markers, including for Alzheimer’s disease and Parkinson’s, as well as many inherited conditions. Before I could see the results, which could tell me I am at a higher risk for some of these conditions, I had to read a statement explaining what these results could mean, not just for myself, but for members of my family too. Maybe I didn’t really care at the time whether I would be more likely to get Alzheimer’s in my old age, but suddenly I realised it might be extremely relevant for my mother or…
- [<strong>Energy transfer (CCEA)</strong>](https://thealevelbiologist.co.uk/energy-transfer/) - Where do we get all our energy from? Food. Where does the energy in food ultimately come from? Plants. Where does the biological energy in plants ultimately come from? Nowhere, they make it themselves through photosynthesis, using multiple types of energy from different sources. So is all (a lot of) the energy available to all living things on Earth down to photosynthesis? It sure is, my biologist friend, it sure is (you know, except the microorganisms that can extract chemical energy from other sources like hydrothermal vents, or the breakdown of matter in soil by fungi, etc.).
- [<strong>Communities and ecosystems</strong>](https://thealevelbiologist.co.uk/communities-and-ecosystems/) - Not all organisms feed the same. Some make their own food and energy, such as photosynthesising plants. These are autotrophs meaning they make their own nutrients, either through light energy or chemical energy. Some bacteria living in extreme conditions such as deep sea vents rely on chemical reactions to derive energy. Although still autotrophic, these are chemoautotrophic while the photosynthesising organisms are photoautotrophic. Both are…
- [<strong>Speciation and natural selection</strong>](https://thealevelbiologist.co.uk/speciation-and-natural-selection/) - The only difference between the founder effect and genetic bottlenecks is the way in which the new genetic pool is formed. In the founder effect the new pool is formed when a few individuals from a population become geographically isolated, while in genetic bottlenecks the new gene pool is formed when only a few individuals from a population survive a mass disaster, or are the only ones to breed.
- [<strong>Gene pool (WJEC)</strong>](https://thealevelbiologist.co.uk/gene-pool/) - This is essentially a way of thinking about all the individuals in a population contributing their alleles towards the overall allele frequency. The extent of different alleles present gives the genetic diversity of a population.
- [<strong>Causes of variation between individuals</strong>](https://thealevelbiologist.co.uk/causes-of-variation-between-individuals/) - It’s not just what genes we have though, it’s also about whether they are switched on or off, when they are switched on or off, and in which particular cells they are switched on or off. Us and chimps share a great deal of our genotype (genetic makeup), more than 98%, yet we can agree that there are significant differences between us that make us distinct species. Features such as height, predisposition to illness, height and weight, or even behaviours such as risk-taking have been linked exclusively or partly to certain genes.
- [<strong>☀️ Mutagens, carcinogens and oncogenes</strong>](https://thealevelbiologist.co.uk/mutagens-carcinogens-and-oncogenes/) - Mutagens are things that can cause mutations in DNA, whether at the base level or chromosome level. Many DNA mutations are the cause of cancer, therefore mutagens can be expected to also be carcinogens (things that can cause cancer). These factors can be physical, such as UV radiation from the Sun or the radioactivity of certain chemicals such as carbon 14 (14C). They can also be chemical such as chelating agents (which bind to DNA between bases and can cause frameshifts) like ethidium bromide (mutagen), or indeed asbestos (carcinogen).
- [<strong>Gene mutation in sickle cell anaemia and chromosome mutation in Down's syndrome</strong>](https://thealevelbiologist.co.uk/gene-mutation-in-sickle-cell-anaemia-and-chromosome-mutation-in-downs-syndrome/) - Sickle cell anaemia is a part of sickle cell disease which is a genetic condition affecting the haemoglobin in our red blood cells. This impairs its function of carrying oxygen in the blood and hence can cause symptoms of anaemia such as dizziness, rapid heart rate and fatigue. Quite rarely, a condition is caused by a simple point mutation of just one DNA base. This is the case in sickle cell anaemia. The single change, in this case a substitution, happens to result in a different amino acid being coded for altogether, as the codon the mutated base is part of codes for valine instead of glutamic acid in this case.
- [<strong>✖️ Sex linkage in haemophilia and Duchenne muscular dystrophy</strong>](https://thealevelbiologist.co.uk/sex-linkage-in-haemophilia-and-duchenne-muscular-dystrophy/) - If for example the allele on the affected X chromosome means that an essential protein isn’t being made, the carrier XX child has another unaffected X chromosome to fall back on and be able to produce the essential protein. The carrier XY child only has the affected X chromosome and cannot make the protein. This results in an illness for example, such as haemophilia. Haemophilia is a blood clotting disorder in which excessive bleeding takes place because the platelet plug and fibrin which are supposed to stop bleeding do not work fully.
- [<strong>Chi squared test</strong>](https://thealevelbiologist.co.uk/chi-squared-test/) - The chi-squared value we obtain from the chi-squared test is put against a probability scale. The probability refers to the probability that for a given chi-squared value (which is defined by how different our observation is from what we would expect), what we observe really is different to what we expect to a significant extent that enables us to reject the null hypothesis.
- [<strong>Alleles and Mendelian inheritance</strong>](https://thealevelbiologist.co.uk/alleles-and-mendelian-inheritance/) - The entirety of genetic material in an organism is called a genotype. It can also refer to specific things, like a genotype for a certain trait in a given organism. Humans have 2 sets of chromosomes, so for each distinct chromosome e.g. chromosome 1, there are two copies. Its expression, however (that is what protein a gene encodes, and what that protein ends up doing in the organism) is a separate entity which is subject to environmental influence. This is called the phenotype.
- [<strong>Parasites (WJEC)</strong>](https://thealevelbiologist.co.uk/parasites/) - Parasites are highly specialised organisms that derive food from their host, at its expense. Examples include the tapeworm (Taenia) as well as lice (Pediculus), both body and hair lice. Tapeworms reside in the small intestine where they can conveniently tap into the host’s nutrients, and so interfere with the normal absorption of the host’s nutrients into its bloodstream, thereby depriving the host to potentially dangerous levels of malnutrition and other side effects such as anaemia and fatigue.
- [<strong>Herbivore and carnivore adaptations</strong>](https://thealevelbiologist.co.uk/herbivore-adaptations/) - Herbivores adapted to a high cellulose diet such as ruminants have specialised teeth. They do not have incisors which are used to tear flesh in carnivores. Instead, they have a dental pad that helps chew plants. Looks so weird, took me a while to understand what was going on.
- [<strong>Human gut adaptations and digestion</strong>](https://thealevelbiologist.co.uk/human-gut-adaptations-and-digestion/) - Human teeth show omnivorous mixed shapes, such as incisors for biting, canines for tearing, premolars for grinding and molars for crushing. Not needing to use the wisdom teeth at the back of the mouth for grinding tough plants has led to what is about to become their extinction in humans. Compared to herbivores and carnivores, human teeth are not…
- [<strong>Unicellular nutrition in Amoeba and multicellular nutrition in Hydra</strong>](https://thealevelbiologist.co.uk/unicellular-nutrition-in-amoeba/) - Single cells such as Amoeba absorb food particles from their environment and digest them directly inside themselves (their single cell). There is no designated area of the cell where phagocytosis takes place as the food gets absorbed. Pseudopods can extend out of the cell to aid with capturing the food. During absorption, vesicles within the plasma membrane of Amoeba can be formed to imbibe the food particles.
- [<strong>Types of nutrition</strong>](https://thealevelbiologist.co.uk/types-of-nutrition/) - Organisms that cannot make their own organic molecules using simpler molecules found in their environment, rely on feeding on those that can. These are heterotrophs and include humans. Since heterotrophs lack any ability to convert light energy or the electron donating potential from certain chemicals into reactions to produce the carbohydrates, lipids and proteins needed for life, they extract them from primary producers such as plants, or other heterotrophs at…
- [<strong>Seed, fruit, germination and the hormone gibberellin</strong>](https://thealevelbiologist.co.uk/seed-fruit-germination-and-the-hormone-gibberellin/) - Following fertilisation, the new seed is carried in fruit and can finally give rise to a new plant through germination at a location potentially further away than the parent plant. Fruit serves this spreading purpose by containing nutrients appealing to various animals which consume them and expel their seeds through defecation at a more distant place.
- [<strong>Pollination and double-fertilisation</strong>](https://thealevelbiologist.co.uk/pollination-and-double-fertilisation/) - Similarly to mammalian gametes, precursor pollen cells undergo meiosis to form 4 offspring cells that become the mature pollen grains. These have specific structure that take part in different aspects of fertilisation, namely the generative nucleus which gives rise to the male gametes proper and contributes to the final zygote once in the ovule, as well as the tube nucleus whose function is to transport the pollen to the embryo sac in the ovule.
- [<strong>Flowers, pollen and ovules</strong>](https://thealevelbiologist.co.uk/flowers-pollen-and-ovules/) - Yes, we are about to learn about plant reproduction and the events that lead to seeds! In terms of the formation of pollen grains and embryo sacs, the sequence of meiosis and mitosis between precursor stages of development is similar to that in mammals. Instead of mammalian testes and ovaries, plants have equivalent structures called anthers and ovules.
- [<strong>Supporting biodiversity</strong>](https://thealevelbiologist.co.uk/supporting-biodiversity/) - As such, Areas of Special Scientific Interest (ASSI) are regions that represent the best of wildlife, and hold great value as natural communities. The Environment Order in Northern Ireland empowers anyone who obtains approval from the Department of Agriculture, Environment and Rural Affairs, and gives 24-hour notice to a landowner, to enter their land and inspect it in order to determine whether it qualifies as an ASSI.
- [<strong>Human environmental impact</strong>](https://thealevelbiologist.co.uk/human-environmental-impact/) - Human activities such as intensive farming can negatively impact biodiversity. Various practices limit this impact, and can even improve biodiversity. These practices include polyculture rather than monoculture, crop rotation, hedgerow conservation and maintenance, predator strips at field margins, and integrated pest management and biological control.
- [<strong>The Five Kingdoms</strong>](https://thealevelbiologist.co.uk/the-five-kingdoms/) - Pictured Lactobacillus is a bacterium added to so-called “probiotic” foods. Archaea look similar to bacteria, so weren’t distinguished for a while, before molecular biology revealed that their genes and protein synthesis machinery are very different and more closely related to those of eukaryotes. Many famous archaea are what’s called extremophiles because they were found in extreme environments such as boiling…
- [<strong>Taxonomy</strong>](https://thealevelbiologist.co.uk/ccea-biodiversity/taxonomy/) - In the old days, a species was known as a collection of individuals similar enough in resemblance to be put in the same box. Taxonomy refers to the classification of living things by giving unique names to each species, and creating a hierarchy based on evolutionary descent.
- [<strong>Measuring Diversity</strong>](https://thealevelbiologist.co.uk/ccea-biodiversity/measuring-diversity/) - The distribution of individuals to species is important in determining a community’s diversity. The above example is easy enough, but for most purposes a formula is needed. This formula measures the index of diversity a.k.a. Simpson’s index of diversity, which is simply a measure of diversity in a community.
- [<strong>Diversity Amongst Organisms</strong>](https://thealevelbiologist.co.uk/diversity-amongst-organisms/) - The diversity of life is built on the same biochemical basis. All life operates with carbohydrates, lipids, nucleic acids and proteins. These building blocks have different properties and serve to function as structural and functional components such as cell walls, enzymes, genetic material, metabolites, energy stores, etc. Just as 4 DNA variables (adenine, guanine, cytosine and thymine) can serve to encode the entire genetic diversity of life, all these basic classes of chemicals together can create so many different configurations of life that it generates diversity of organisms at the individual and species level.
- [<strong>Population distribution</strong>](https://thealevelbiologist.co.uk/population-distribution/) - A niche is the interaction, or way of life, of a species, population or individual in relation to all others within an ecosystem. It’s how it behaves, what it eats, how it reproduces, where it sleeps, etc.; a species’ niche is determined by both biotic factors (such as competition and predation) and abiotic factors. Different things may determine the population sizes within an…
- [<strong>Adaptation to the environment</strong>](https://thealevelbiologist.co.uk/adaptation-to-the-environment/) - As previously seen with plants adapted to wet or dry conditions, different species employ a variety of adaptations to match their environment. The sum of all adaptations comprises behavioural, physiological and morphological adaptations. This lil’ fella is an adorbsssss little mammal that lives in North America in very dry/desert-type areas. It is a master at preserving its water, and can live without ever actually drinking water at all. Some of its adaptations are behavioural such as being inactive during the day and being active at night when it’s colder, as well as burrowing into sand, and bathing in sand to keep its hairs free of too much oil which would decrease their ability to insulate the body.
- [<strong>Plant transport</strong>](https://thealevelbiologist.co.uk/plant-transport/) - What you can see above is a delicious slice of pineapple. OK, it’s not. That is a slice of a root. Roots, as you may have seen in real life, are hairy. All those tiny and not so tiny root hairs buried into the soil greatly increase the surface area of the root. The cell sap (i.e. cell juice) has a lower water potential than the fluid found in the soil, so the water in the soil kindly makes its way into the thirsty awaiting root.
- [<strong>Earthworm, insect, fish and mammal vascular systems</strong>](https://thealevelbiologist.co.uk/earthworm-insect-fish-and-mammal-vascular-systems/) - Earthworms have a system similar to mammals as they have vascularisation (blood vessels), and transport gases dissolved in the blood which is pumped by 5 “hearts”. Unlike other organisms, they… well, they have 5 hearts! Insects do not carry respiratory gases in the blood, and have an open circulatory system. Their heart is towards the back of the body (dorsal) and has a tube shape.
- [<strong>Menstruation, gestation and lactation</strong>](https://thealevelbiologist.co.uk/menstruation-gestation-and-lactation/) - What happens when you have a complex interplay between 4 different variables? The Mammalian Oestrus is Controlled by 4 Hormones: FSH, LH (pituitary gland), Progesterone and Oestrogen (ovaries). FSH is follicle-stimulating hormone (it stimulated follicles to develop which are immature eggs surrounded by other cells).
- [<strong>Ovary, testis, oogenesis and spermatogenesis</strong>](https://thealevelbiologist.co.uk/ovary-testis-oogenesis-and-spermatogenesis/) - Ovaries produce egg cells released one (sometimes two! or many more if induced by hormones e.g. IVF) at a time, which travel from each ovary (they take turns to release an egg) down the Fallopian tube towards the uterus. The egg can undergo fertilisation by a sperm cell found in the Fallopian tube, and develop into a zygote, attach to the upper lining of the womb (endometrium) and start pregnancy; or be shed alongside part of the endometrium two weeks after ovulation (egg release from the ovary) – this is…
- [<strong>Blood clotting</strong>](https://thealevelbiologist.co.uk/blood-clotting/) - Upon disturbance of the cells lining a blood vessel, a cascade of events leads up to the coagulation of the blood and restoration of a protective barrier between the tissue and the environment, preventing further bleeding (hemostasis). Blood turns from a liquid to a gel. Many aspects that cause coagulation also contribute to defence against pathogens. For example, as the blood clots, it traps bacteria. Some clotting components are also toxic to some bacteria.
- [<strong>Blood and tissue fluid</strong>](https://thealevelbiologist.co.uk/tissue-fluid/) - Plasma is a water solution containing proteins, sugars, clotting factors (as well as platelets involved in clotting), hormones, electrolytes, carbon dioxide and oxygen. Erythrocytes are red blood cells/RBC (and also the most common blood cells) carrying haemoglobin around the body. Haemoglobin can bind and release oxygen and is central to aerobic respiration.
- [<strong>Mammalian heart</strong>](https://thealevelbiologist.co.uk/mammalian-heart/) - The heart contains two atria, two ventricles, the septa, AV-valves (tricuspid and bicuspid), chordae tendinae and papillary muscles. Septa describe the dividing walls between the right and left atria and ventricles respectively. The chordae tendinae a.k.a. heart strings, are attached to the papillary muscles which prevent the walls collapsing onto themselves during…
- [<strong>Mammalian circulation (CCEA)</strong>](https://thealevelbiologist.co.uk/mammalian-circulation/) - Cells in mammals require a constant supply of nutrients and oxygen, and a way to remove waste products. Blood is great, as it does all that. Blood needs a way of getting to all cells of the body, a way to… circulate. Without that, blood would just get pulled by gravity towards the centre of the earth. Not a pretty sight I’m afraid.
- [<strong>Mass Transport</strong>](https://thealevelbiologist.co.uk/mass-transport/) - Gas exchange in large multicellular organisms is achieved by organs which have a large surface area and so are able to successfully provide the substances the organism needs in order to survive. In humans this is achieved by the lungs. But how does the oxygen acquired by the lungs actually reach every single cell of the body? A network of sorts is needed to do that. Many bigger and smaller tubes would come in handy. They would form like a… circulatory system. Oh wait, that’s precisely what mammals have: a circulatory system made of arteries, veins, capillaries, etc.
- [<strong>Structure of the angiosperm leaf</strong>](https://thealevelbiologist.co.uk/structure-of-the-angiosperm-leaf/) - Air with its carbon dioxide (necessary for photosynthesis) enters the leaf through the stomata. Stomata are holes on the leaf surface, made by the guard cells. They can open and close depending on environmental factors such as humidity, temperature and wind. This controls the amount of water loss. Oxygen, the byproduct of photosynthesis, also leaves the leaf through the...
- [<strong>Human gas exchange</strong>](https://thealevelbiologist.co.uk/human-gas-exchange/) - The capillaries surrounding alveoli are so narrow, that the red blood cells have to be squished in order to pass through. This shortens the diffusion pathway, which in turn increases the rate of diffusion. What allows diffusion to take place, of course, is the concentration gradient formed between the air in the alveoli and the red blood cells. Red blood cells deprived of oxygen and loaded with carbon dioxide (the blue/purple ones) will release carbon dioxide into the fresh air, then take up oxygen from…
- [<strong>Insect and fish gas exchange</strong>](https://thealevelbiologist.co.uk/fish-gas-exchange/) - Insects have a tracheal system made up of many tracheae which branch into smaller tracheoles. All tracheae connect to the exoskeleton of the insect, so that air diffuses in and out through the spiracles. The technical terms highlighted above are important in describing what really is just a bunch of holes and tubes. Here’s a video that describes what happens. Don’t worry about the overly detailed labels. Just enjoy the…
- [<strong>Gas Exchange Adaptations</strong>](https://thealevelbiologist.co.uk/gas-exchange-adaptations/) - What this basically means is that the larger an organism gets, the less surface area is available to serve its increasing needs due to its increasing volume. So what adaptations do larger organisms have to cope with the large demand for substance and heat…
- [<strong>Nerve impulses and the motor neurone</strong>](https://thealevelbiologist.co.uk/nerve-impulses-and-the-motor-neurone/) - Let’s delve into the basics of nervous transmission by looking at a motor neurone. Here is the structure of a myelinated motor neurone. Labelled “insulating sheath”, the myelin sheath is responsible for protecting the electrical impulses that run across the neurone.
- [<strong>Response to stimuli and the spinal cord</strong>](https://thealevelbiologist.co.uk/response-to-stimuli-and-the-spinal-cord/) - The spinal cord consists of a central canal filled with cerebrospinal fluid, and grey (H shape) and white matter. The CNS is composed of the brain and spinal cord, while the PNS consists of nerves which are connected to the CNS and reach the rest of the body.
- [<strong>Adaptation</strong>](https://thealevelbiologist.co.uk/adaptation/) - So that’s the last and loveliest new term: niche. It rhymes with quiche. A niche is the interaction, or way of life, of a species, population or individual in relation to all others within an ecosystem. It’s how it behaves, what it eats, how it reproduces, where it sleeps, etc.; a species’ niche is determined by both biotic factors (such as competition and predation) and…
- [<strong>Measuring biodiversity and natural selection</strong>](https://thealevelbiologist.co.uk/measuring-biodiversity/) - Different populations correspond to defined areas – habitats. This is essentially a way of thinking about all the individuals in a population contributing their alleles towards the overall allele frequency. In the wild, each species may exist as one population or multiple populations.
- [<strong>Kingdoms: Prokaryotae, Protoctista, Plantae, Fungi, Animalia</strong>](https://thealevelbiologist.co.uk/kingdoms-prokaryotae-protoctista-plantae-fungi-animalia/) - The five-kingdom system of Prokaryotae, Protoctista, Plantae, Fungi and Animalia is already half a century old, has been up for debate as well, and will probably continue to evolve as we learn more about new species and the relationships between different kinds of organism. So, without further ado, let’s learn the basic principles of these kingdoms and what kind of organisms they represent.
- [<strong>Classification of organisms</strong>](https://thealevelbiologist.co.uk/classification-of-organisms/) - A species is defined in terms of observable physical features as well as the ability to produce fertile offspring. In the old days, a species was known as a collection of individuals similar enough in resemblance to be put in the same box. This was purely based on physical features. Today we know that similar physical characteristics on their own aren’t enough to define a species.
- [<strong>Structure and function of a mesophytic leaf</strong>](https://thealevelbiologist.co.uk/structure-and-function-of-a-mesophytic-leaf/) - The large surface area of most leaves maximises photosynthesis, while the tightly packed palisade mesophyll cells contain chlorophyll to carry out photosynthesis to meet the plant’s energy needs. The mesophyll cells (more specifically, the spongy mesophyll) are surrounded by quite a lot of empty space for air to mingle around, providing plenty of surface area for gas exchange by diffusion. They are tightly packed and perform photosynthesis.
- [Absorption by the epithelium](https://thealevelbiologist.co.uk/absorption-by-the-epithelium/) - Starch is hydrolysed to disaccharides and trisaccharides before further reactions by other enzymes convert the products into glucose, the ultimate usable nutrient. The hydrolysis of starch is catalysed by amylase. As this step of carbohydrate digestion begins in the mouth, initially non-sweet carbs like potatoes or rice gradually sweeten in taste before being swallowed for their digestion to continue.
- [<strong>⚙️ Ileum structure and function</strong>](https://thealevelbiologist.co.uk/tissues-and-organs/ileum-structure-and-function/) - The mammalian digestive tract ileum is the final section of the small intestine. The first and second section of the small intestine respectively are the duodenum and the jejunum. The duodenum is where proteins and lipids get broken down with the aid of liver bile and stomach chyme, while the ileum is where bile acids and vitamin B12 get absorbed.
- [<strong>Cell Specialisation</strong>](https://thealevelbiologist.co.uk/cell-specialisation/) - Cells differentiate into specific structures and functions, and organise themselves as such into tissues. For anyone who’s seen the film Life starring our first Martian life form called Calvin, there is a way that cells can associate the way Calvin does. In this case, cells aren’t at all differentiated to do different things in tissues, organs, etc. but instead maintain their single cell status among equal single cells.
- [<strong>Kidney failure</strong>](https://thealevelbiologist.co.uk/kidney-disease/) - The mechanisms of development of these symptoms are high levels of urea in the blood (nausea, weight loss, bloody urine), build-up of phosphates in the blood (itching, bone damage, muscle cramps), buildup of potassium in the blood (arrhythmia, paralysis), and failure to remove excess fluids (swelling, shortage of breath). Addressing the underlying issues priming kidney disease, such as lifestyle factors like diet can revert kidney disease in its incipient stage. Once kidney function has ceased, kidney failure can be treated with dialysis or a kidney transplant.
- [<strong>Mammalian kidney structure and function</strong>](https://thealevelbiologist.co.uk/mammalian-kidney-structure-and-function/) - There are systems in place that keep the blood at the right composition and pressure. The hypothalamus and posterior pituitary in the brain release a hormone into the blood that reaches the kidney and enables its cells to take up more water, to prevent it being wasted in urine as the case may be. This is detected by osmoreceptors. I’ve never done the kidney so I spent my post-A levels life in total kidney ignorance and utter lack of knowledge of my urination habits and their complexity, oh what a fool I have been. You on the other hand are going to have the damn honour of actually having a clue about how the brain and the kidneys freshen our blood up all the time. Oh ye enlightened children, rise.
- [<strong>Homeostasis and negative feedback (WJEC)</strong>](https://thealevelbiologist.co.uk/homeostasis-and-negative-feedback/) - The internal environment of our bodies is constantly kept within strict limits. Take for example temperature. It must be a challenge keeping our fleshy selves at 37°C while the outside fluctuates wildly! Or how about blood glucose concentration? We’ve all heard of diabetes – if it goes too high our organs sustain damage, if it goes too low a coma may be induced or even death.
- [<strong>Planetary boundaries</strong>](https://thealevelbiologist.co.uk/planetary-boundaries/) - The concept of planetary boundaries was developed to quantify and monitor the broadest areas of environmental impact that would affect human habitability on Earth, and with that, define and quantify the limits within which human activity could safely be conducted. So far, nine boundaries have been defined, with more open to being added. Three of these are thought to have already been breached: climate change, loss of biodiversity and biogeochemical flow.
- [<strong>Politics and the environment</strong>](https://thealevelbiologist.co.uk/politics-and-the-environment/) - As seen previously, conservation efforts cannot succeed outside of a deep consideration of the balance between these efforts and the wider human context including local economies, human practices and beliefs, etc. For example, many products of wild animals that are becoming endangered such as rhinos, elephants and tigers are sought solely due to an often, if not always, unfounded but very strong belief that these animal products can heal disease or bring good fortune.
- [<strong>Agriculture</strong>](https://thealevelbiologist.co.uk/agriculture/) - A strategy to maximise net productivity is an integrated system. Put simply, this is a self-contained nutrient recycling approach which involves using manure as plant fertiliser, and leftover plant “waste” as additional feed for animals. There are many issues (economical, social, ethical) surrounding intensive farming across the globe. Here are a few: 1. Prioritising land – since so much energy is inherently wasted every time plants are used for anything else apart from direct eating by us, it is both an economical and social issue to decide whether so much land should be used for plants grown simply to feed animals which then pass on a tiny fraction of energy onto us.
- [<strong>Fighting viruses</strong>](https://thealevelbiologist.co.uk/fighting-viruses/) - So far we’ve learnt that viruses aren’t cells. They aren’t alive. They’re just biological elements that interact with preexisting life forms that are actually capable of carrying out life chemistry on their behalf. In some ways viruses are biological entities like seeds.
- [<strong>⚕️ Penicillin and tetracycline</strong>](https://thealevelbiologist.co.uk/penicillin-and-tetracycline/) - Penicillin is an antibiotic used against gram positive bacteria. It doesn’t work on gram negative bacteria because their outer membrane (cell envelope) protects against it. Penicillin works by interfering with the production of the cell wall component murein, and as gram positive bacteria have so much of it and at the outer surface, losing it kills them off.
- [<strong>Nervous and hormonal control of digestion</strong>](https://thealevelbiologist.co.uk/nervous-and-hormonal-control-of-digestion/) - Digestion is the process by which large biological molecules such as carbohydrates, lipids and proteins get hydrolysed into their smaller constituent molecules so they may be absorbed across cell membranes.
- [<strong>Instruments and equipment</strong>](https://thealevelbiologist.co.uk/instruments-and-equipment/) - The actual use of various instruments and equipment is part of your practicals. Oh wait, no. An experimental bench is about to be summoned onto your computer! This is going to be exciting!
- [<strong>Training and supplements</strong>](https://thealevelbiologist.co.uk/training-and-supplements/) - Training is another key factor that determines aerobic fitness, and it has the power to significantly improve it. The F.I.T.T. factors of the exercise programme regulate the fitness outcome. These are frequency, intensity, type and time.
- [<strong>Origin of life</strong>](https://thealevelbiologist.co.uk/origin-of-life/) - The history of the Earth has been colourful as today’s Earth is rather different than it was in its beginning. For example, the atmosphere of the Earth did not have the oxygen and carbon dioxide concentrations it has today. Oxygen was added to the atmosphere by photosynthesising plants, and they needed carbon dioxide in the first place to photosynthesise.
- [<strong>Interpreting heart function data</strong>](https://thealevelbiologist.co.uk/interpreting-heart-function-data/) - Heart function data can come in many forms including ECG (electrocardiogram) traces and pressure changes. The aim of collecting this data is to monitor the activity of the heart and identify any issues pertaining to the circulatory system.
- [<strong>Integrated pest management</strong>](https://thealevelbiologist.co.uk/integrated-pest-management/) - Pesticides such as weedkillers (herbicides) and insecticides can be selective (or non-selective) and systemic (or contact). Selective plant protection chemicals only affect certain species, commonly certain weeds. Non-selective chemicals are useful in a large breakout, but risk contaminating wider areas, and weeds as well as other plants.
- [<strong>Chordata (e.g. cat) body form</strong>](https://thealevelbiologist.co.uk/chordata-eg-cat-body-form-and-feeding/) - The Chordata phylum covers mammals and birds, and is distinguished by the spinal cord that gives the body its structural support alongside a jointed system of calcified bones. Chordata species are both bilaterally symmetrical and segmented, and the gut similarly includes both a mouth and an anus, with specialised digestion regions. Saliva and mastication (chewing) prepare ingested food into a bolus which passes down the esophagus upon swallowing, into the stomach.
- [<strong>Selection (CCEA)</strong>](https://thealevelbiologist.co.uk/mechanisms-change/selection/) - Here is an all-time classic example. The most frequent initial moth colour in a population landing on tree trunks was dark, to match that of the tree trunks. Few moths could get away with being light-coloured. Once the tree trunks were painted white, the former moths became very apparent to predators, and so the light-coloured moths evaded predation much better and survived to reproduce. Essentially, the tables had turned!
- [<strong>Causes of Variation</strong>](https://thealevelbiologist.co.uk/causes-of-variation/) - Variation is central to life itself. Variation is what makes every single individual… an individual. Without variation, the evolution of different species would not be possible. What is the cause of variation?
- [<strong>Hardy-Weinberg principle (CCEA)</strong>](https://thealevelbiologist.co.uk/hardy-weinberg-principle/) - Firstly, there are criteria for when this principle may be applied to a population: 1. Random mating must take place. 2. No migration must occur either inwards or outwards of the population. 3. No mutations must arise in the population. 4. No natural selection must take place due to one trait being better or worse adapted to the environment.
- [<strong>Genetic interactions and properties</strong>](https://thealevelbiologist.co.uk/genetic-interactions-and-properties/) - Epistasis refers to the interdependence of separate genes and their effects. These interactions can be vast and subtle, and create many unexpected outcomes. It also enables a huge diversity of phenotype and potential for evolution. In this silly example, a gene inducing baldness creates an outcome that interjects the outcome of genes for hair colour, as the hair would not get to show itself anyway. Through this interaction, the different alleles for the colour gene are suddenly and non-linearly disabled.
- [<strong>Sex determination and sex linkage</strong>](https://thealevelbiologist.co.uk/sex-determination-and-sex-linkage/) - While some species are hermaphroditic (each individual has two sexes), others have sex determination in separate individuals based on environmental cues during development such as temperature and resource availability, or based on genetic factors e.g. chromosomes. Some factors that can shift an individual’s sex in some species include their size, parasitic infection or competition. For example, crustaceans such as shrimp are born without a sex, and are prone to being directed by various cues. A paramyxean parasite was found to drive shrimps to turn female, causing an imbalance in the population and disrupting marine habitats.
- [<strong>⚖️ Ethics and safety of gene technology</strong>](https://thealevelbiologist.co.uk/genetic-manipulation-for-research-ethical-implications/) - Following the successful first complete sequencing of a human genome, an updated project called 100,000 Genome Project in the UK has been launched by the government through the NHS to sequence the genomes of rare disease and cancer patients as well as their families. The insights gleaned from this data may serve to find treatments, as well as provide a rich source for further research that may be relevant to other disciplines in molecular biology and epidemiology.
- [<strong>Genome sequencing</strong>](https://thealevelbiologist.co.uk/genome-sequencing/) - Simple genomes such as those of viruses can enable a relatively straightforward effort of assigning proteins to each gene in the genome, and thus creating a database of them. This is known as a proteome. The information gleaned from a virus proteome, for example, can inform vaccination targets by selecting appropriate antigens such as elements of the viral capsid. Other exciting synthetic biology applications can be explored such as glowing beer, synthesising specific compounds useful in medicine or manufacturing using...
- [<strong>Gene Therapy</strong>](https://thealevelbiologist.co.uk/gene-therapy/) - Gene therapy involves inserting a functional gene into a patient who lacks it, or needs supplementary support. This works for conditions which are caused by a single faulty gene rather than multiple genes. The vector used to deliver the gene is a harmless virus. Once the new DNA is taken up in the cell nucleus, the gene is expressed like any other gene.
- [<strong>⚰️ Species Extinction</strong>](https://thealevelbiologist.co.uk/species-extinction/) - A seemingly small increase of several degrees Celsius can have vast effects on the Earth’s crop plants, insect pests and wild plants and animals. For example, the life cycle of many insect pests is tightly regulated by temperature. A very finely tuned heating up or cooling down triggers development and reproduction. The result of warming is a faster life cycle which means that instead of one generation arising yearly, there might be two or three generations arising yearly instead. This poses problems for the protection of crop plants.
- [<strong>Meiosis</strong>](https://thealevelbiologist.co.uk/meiosis/) - Meiosis is a type of cell division which results in 4 cells that are genetically non-identical from one parent cell. In order for once cell to divide to result in 4 cells, how many divisions must take place?
- [<strong>Mitosis</strong>](https://thealevelbiologist.co.uk/mitosis/) - Multi-cellular organisms such as ourselves are… multi-cellular. This point must be emphasised in learning about mitosis because mitosis is the process by which this is possible. A bacterium is a cell which divides to produce 2 bacteria, yet that cell is the organism itself. Multi-cellular organisms require a process by which one cell divides into two, those two into four, and so forth, until a gargantuan number of cells come alive. Cells are organised in tissues (such as skeletal muscle), tissues are organised in organs (such as the skin), and organs are organised into systems (such as the nervous system). The various systems make up the live organism.
- [<strong>Chromosomes</strong>](https://thealevelbiologist.co.uk/chromosomes/) - DNA and chromosomes may seem like completely separate things. Well, they’re not. In fact, all chromosomes are individual DNA molecules coiled and twisted around, because DNA is huge. At least in eukaryotes it is. That’s one of the first differences between eukaryotes and prokaryotes in their DNA – prokaryotes have less DNA.
- [<strong>Cell Cycle (CCEA)</strong>](https://thealevelbiologist.co.uk/cell-cycle/) - The cell cycle refers to the distinct stages through which a cell goes, from the moment it becomes a cell to the moment it divides to result in 2 separate cells. Bear in mind that some cells cease to divide any longer after a certain period of time, depending on cell type. If that’s the case, they are said to be in resting phase termed G0.
- [<strong>Nitrogen Cycles (WJEC)</strong>](https://thealevelbiologist.co.uk/nitrogen-cycle/) - Nitrogen is an important element in organisms, taking part in one of their most important building blocks – amino acids. That’s not to mention DNA itself… In the nitrogen cycle there are two stages of N presence: the atmosphere and the ground. Whenever N is in the atmosphere it’s in the form of nitrogen gas, N2 which of course is what most of the air is made of. In the ground, N is found in ammonia (NH3), nitrite (NO2-) and nitrate (NO3-).
- [<strong>Carbon Cycles (WJEC)</strong>](https://thealevelbiologist.co.uk/carbon-cycle/) - The words on everyone’s lips when it comes to carbon are greenhouse gas and global warming. Aside from CO2, methane is also a greenhouse gas – that is, it has the potential to increase the Earth’s average temperature. Greenhouse gases are responsible for the Earth being about 33 degrees Celsius warmer than it would be without them.
- [<strong>Succession (WJEC)</strong>](https://thealevelbiologist.co.uk/succession/) - It may be classified as primary succession or secondary succession. The difference is that the above is primary i.e. it begins with totally barren land devoid of any nutrients or other abiotic factors (water, wind, temperature) conductive to life thriving, while secondary succession occurs after an already-thriving community has been wiped out by natural disasters such as…
- [<strong>Biomass transfer</strong>](https://thealevelbiologist.co.uk/biomass-transfer/) - And whatever eats the plant will also lose energy through excretion for example, so whatever eats this herbivore will have even less energy available to themselves. Therefore, at each trophic level in the energy transfer (feeding) hierarchy there is a net loss of energy. This results in a pyramid. The plants at the bottom are the photosynthesising primary producers. They hold the most energy (Joules) and are fed on by herbivores – primary consumers.
- [<strong>☘️ Sampling Organisms</strong>](https://thealevelbiologist.co.uk/population-size-ecosystems/sampling-organisms/) - Transects are tapes (like above) placed across an area which has some form of gradient caused by abiotic factors which directly determines the distribution and abundance of the organisms present. For example, a beach is not suited for random sampling because there are clear zones ranging from the low population zone near the sea, to the more densely inhabited areas further up the shore. In this case the best way of obtaining useful data is by…
- [<strong>Population growth (WJEC)</strong>](https://thealevelbiologist.co.uk/population-size-ecosystems/population-growth/) - Human populations grow and shrink due the balance between births and deaths. The number of births per 1000 people is called the birth rate, and the number of deaths per 1000 people is the death rate.
- [<strong>Polypeptide synthesis and processing</strong>](https://thealevelbiologist.co.uk/polypeptide-synthesis-and-processing/) - Proteins are made up of amino acids linked by peptide bonds, therefore a protein may be referred to as a polypeptide (of course, some proteins such as haemoglobin have extra bits to them). All are encoded for by the information stored in DNA. Let’s see how exactly this happens.
- [<strong>DNA Replication (WJEC)</strong>](https://thealevelbiologist.co.uk/dna-replication/) - The DNA molecule replicates by providing each of its strands as a template for 2 new DNA molecules, each having one entire new strand, and one entire old strand from the parent DNA molecule. This is called the semi-conservative…
- [DNA Structure (WJEC)](https://thealevelbiologist.co.uk/dna-structure/) - DNA is a double helix i.e. two individual strands running along each other in an anti-parallel way, connected to one another by relatively weak hydrogen bonds. DNA’s structure can be learned easily by thinking about the strands and the “stuff in-between” separately.
- [<strong>Human effects on ecosystems</strong>](https://thealevelbiologist.co.uk/ecosystems/human-effects-on-ecosystems/) - Aside from CO2, methane is also a greenhouse gas – that is, it has the potential to increase the Earth’s average temperature. Greenhouse gases are responsible for the Earth being about 33 degrees Celsius warmer than it would be without them. The issue arises when the otherwise slow, natural development of global weather patterns is significantly sped up by the burning of fossil fuels. The receding of the North Pole ice…
- [<strong>Changes in ecosystems</strong>](https://thealevelbiologist.co.uk/changes-in-ecosystems/) - Succession is classified as primary succession or secondary succession. The difference is that primary i.e. it begins with totally barren land devoid of any nutrients or other abiotic factors (water, wind, temperature) conductive to life thriving, while secondary succession occurs after natural disasters such as a wild fire.
- [<strong>Energy transfer through ecosystems</strong>](https://thealevelbiologist.co.uk/ecosystems/energy-transfer-through-ecosystems/) - Net productivity is equal to gross productivity minus respiratory loss. In both terms, productivity refers to the amount of leftover useful tissue such as cereals or animal flesh. Gross primary production (GPP) is the chemical energy stored in plant biomass in a specific area or volume, while net primary production (NPP) is the chemical energy store in plant biomass after accounting for respiratory losses (R) to the environment.
- [<strong>The nature of ecosystems</strong>](https://thealevelbiologist.co.uk/the-nature-of-ecosystems/) - A community is made up of the various populations in a habitat. So the summation of all the living things in a given area is called a community. What then is an ecosystem? An ecosystem comprises the community of living organisms in a habitat, together with all the non-living components such as water, soil, temperature, etc. called abiotic factors. Why are different organisms of different species able to coexist in the same habitat?
- [<strong>Osmoregulation and temperature regulation</strong>](https://thealevelbiologist.co.uk/osmoregulation-and-temperature-regulation/) - Osmoregulation refers to the control of water potential of the blood. The blood is complicated, it has all these ions and proteins and stuff. Cells use various things up all the time and some more often than others at different times, night, day, sweat, tears, etc. There are systems in place that keep the blood at the right composition and pressure. The hypothalamus and posterior pituitary in the brain release a hormone into the blood that reaches the kidney and enables its cells to take up more water, to prevent it being wasted in urine as the case may be. This is detected by osmoreceptors.
- [<strong>Control of heart rate in mammals</strong>](https://thealevelbiologist.co.uk/control-of-heart-rate-in-mammals/) - The heart rate must go up because the blood pressure is low, there’s a shortage of oxygen, an excess of CO2 or the pH is too low – some of these go together e.g. O2, CO2 and pH interaction during exercise, stress, etc. The hormone that increases heart rate is noradrenaline. This can be released by the brain’s medulla via the sympathetic neurons when aortic and carotid baroreceptors which sense low blood pressure or chemoreceptors which sense excess or a lack of certain chemicals send signals via sensory neurons.
- [<strong>Detection of light by mammals</strong>](https://thealevelbiologist.co.uk/detection-of-light-by-mammals/) - The retina lines the inside of the eyeball. The macula is the high-density photoreceptor area of the retina found towards the back of the eye. The structure of the retina, width-wise, contains several types of cell. These are interconnected one to the next towards the optic nerve side, as well as horizontally connected amongst them.
- [<strong>Effects of drugs on the nervous system</strong>](https://thealevelbiologist.co.uk/effects-of-drugs-on-the-nervous-system/) - Many chemicals can interfere with nervous transmission in a variety of different ways. We’ll be looking at the effects of nicotine found in tobacco, lidocaine used as an anaesthetic, and cobra venom transmitted via bites. Nicotine is absorbed in the lungs and travels through blood to the brain, where it behaves as acetylcholine, resulting in binding to its respective receptors. This results in a stimulant effect which is the cause of its high addictive potential.
- [<strong>Nervous transmission</strong>](https://thealevelbiologist.co.uk/nervous-transmission/) - Labelled “insulating sheath”, the myelin sheath is responsible for protecting the electrical impulses that run across the neurone. But first, what happens in a resting state where no impulses are being sent? This is the resting potential where the membrane permeability differentiates between sodium (Na+) and potassium (K+) ions so that at any given time there are more Na+ ions outside than inside and more K+ ions inside than…
- [<strong>Structure and function of the mammalian nervous system</strong>](https://thealevelbiologist.co.uk/structure-and-function-of-the-mammalian-nervous-system/) - The spinal cord consists of a central canal filled with cerebrospinal fluid, and grey (H shape) and white matter. Nerves connect to the cord, while the meninges act to protect the cord (alongside the brain). The brain has several key parts: the medulla oblongata, the cerebellum, the cerebrum and the hypothalamus.
- [<strong>Chemical Control in Plants</strong>](https://thealevelbiologist.co.uk/chemical-control-in-plants/) - This ensures plants respond to their environment in a way that best maximises their survival prospects. More light enables better photosynthesis, while growing upwards exposes their leaves to more sunlight. Auxin also suppresses lateral bud growth, so only the apical bud is growing, as it secretes auxin that travels downwards. This is called…
- [<strong>Chemical Control in Mammals</strong>](https://thealevelbiologist.co.uk/chemical-control-in-mammals/) - Mammals secrete hormones via their endocrine glands to control many functions in the body including the stress response, digestion, reproduction, etc. Hormones are chemicals which bind to specific receptors on cells if present, and initiate a response. This is either directly by entering cells and binding transcription factors, or indirectly via a second messenger which then cascades the signal down and activates enzymes.
- [<strong>Optimising and analysing growth</strong>](https://thealevelbiologist.co.uk/optimising-and-analysing-growth/) - Once the right environment is set up (often this means 37 deg. Celsius, shaking the flasks to introduce oxygen bubbles into the solution and optimise growth, leaving plates incubating overnight, etc.), growth can finally be monitored. There are many ways of doing this, such as cell counts, dilution plating, mass and optical methods that detect turbidity.
- [<strong>Culturing microorganisms</strong>](https://thealevelbiologist.co.uk/culturing-microorganisms/) - We don’t want contamination, we just want our specific species that we are culturing and nothing else. The various techniques employed to this end have evolved through time and can even differ between labs and scientists. A flame (Bunsen burner) can be used in the close vicinity of handling the target microorganism and related equipment and reagents, in order to make the surrounding air warm up and rise higher, carrying away…
- [<strong>Bacterial classification</strong>](https://thealevelbiologist.co.uk/bacterial-classification/) - The simplest classification system of bacteria is based on their shape and arrangement. Bacteria come in sphere, rod, spiral, comma and filament shapes, and can be paired up in twos, strings or 3D shapes. Using the diagram, can you figure out what Staphylococcus aureus, Vibrio cholerae and Streptococcus sp. look like?
- [<strong>Microscopy</strong>](https://thealevelbiologist.co.uk/microscopy/) - In light microscopy, light does go through the sample, but the outcome depends on the thickness of the sample. For example, the plant root slice in the diagram (LM) is thin enough to be able to see through the thickness of the sample. Light would also travel freely through air but not various materials of high opacity.
- [<strong>⚙️ Cell Structure</strong>](https://thealevelbiologist.co.uk/cell-structure/) - Prokaryotic ribosomes are smaller than their eukaryotic counterparts; due to their size (and the centrifugation level they separate from the cell at) they are termed 70S ribosomes; the bigger eukaryotic ribosomes are 80S. As previously covered, and their primary defining element, they lack a nucleus; instead, their DNA is a single circular molecule freely present in the cytoplasm and not associated with any proteins such as…
- [<strong>Immobilised enzymes in industry</strong>](https://thealevelbiologist.co.uk/immobilised-enzymes-in-industry/) - Since enzymes are so specific, powerful – many thousands of times faster than some chemical catalysts – and operate at much lower temperatures, too, they are employed in many industries including food and cleaning. These industries work with tremendous amounts of product, so the amount of enzyme used for each reaction would be equally huge and very uneconomical, as enzymes can be expensive to make.
- [<strong>Factors affecting enzyme function</strong>](https://thealevelbiologist.co.uk/factors-affecting-enzyme-function/) - Increasing temperature results in a higher rate of activity, up to a certain point where the enzyme becomes denatured. A high temperature causes the molecule to vibrate, breaking the weak bonds that hold it together, and changing the structure of the enzyme. This process is denaturation. The point at which this happens is usually around 50 – 60 degrees Celsius.
- [<strong>Enzyme structure and action</strong>](https://thealevelbiologist.co.uk/enzyme-structure-and-action/) - The enzyme’s shape is not exactly matched to the substrate, but it is able to accommodate the substrate with a close enough shape into an enzyme-substrate complex and carry out catalysing that reaction. Here is a video of an enzyme catalysing a reaction between two…
- [<strong>Genetic Fingerprinting (AQA)</strong>](https://thealevelbiologist.co.uk/genetic-fingerprinting/) - Any 2 given people share 99.9% of their DNA code. But the differences present in the remaining 0.01% of it are enough to enable reliable identification, with the exception of monozygotic twins. The DNA containing this is called variable number tandem repeats (VNTRs) because they are just sequences of DNA repeated many times.
- [<strong>Differences in DNA between individuals of the same species can be exploited for identification and diagnosis of heritable conditions</strong>](https://thealevelbiologist.co.uk/differences-in-dna-between-individuals-of-the-same-species-can-be-exploited-for-identification-and-diagnosis-of-heritable-conditions/) - Techniques used to identify gene location for a variety of purposes include DNA hybridisation and DNA probes. These involve tagging a DNA strand with a fluorescent agent and binding it to a new strand, the probe, which is complementary to the target gene. The new double-stranded DNA is a hybrid. The extent of binding to the probe (and hence the complementarity between base pairs) is measured by the intensity of fluorescence seen under UV light. This technique can be used to reveal the presence of heritable conditions, drug responses or health risks. You can get this done today!
- [Recombinant DNA Technology](https://thealevelbiologist.co.uk/gene-cloning-and-transfer/) - The mRNA following splicing, on the other hand, has no introns! How can we make DNA from mRNA? Take this arbitrary bit of mRNA: UCCAUGCCAUUUGGG If we had an enzyme which could reverse the transcription back into DNA, this time intron-free, that would be great. We do – it’s called reverse transcriptase and it produces DNA.
- [<strong>Using genome projects</strong>](https://thealevelbiologist.co.uk/using-genome-projects/) - Analysing and storing information about more complex genomes is hindered by non-coding DNA and regulatory genes. Non-coding DNA and regulatory genes take up the vast majority of this type of genome. This means that the actual protein products that genes code for are in the minority…
- [<strong>Gene expression and cancer</strong>](https://thealevelbiologist.co.uk/gene-expression-and-cancer/) - Not all tumours are cancer. Tumours are tissue growths beyond the required tissue growth for healthy functioning. Benign tumours are local and cannot spread. Mostly they pose no direct health risk, and only require medical interventions such as surgery if they interfere with organ, nerve or blood vessel function by their presence (i.e. increasing local pressure). The ability of tumour cells to spread beyond the local tumour is called metastasis and defines malignant tumours which are the basis of cancer. This is also the primary source of death related to tumours.
- [<strong>Regulation of Transcription and Translation</strong>](https://thealevelbiologist.co.uk/regulation-of-transcription-and-translation/) - Transcriptional factors are molecules which can bind DNA and thus initiate transcription. Most of the time these are inactive in the cytoplasm because they have an inhibitor attached to them. Hormones like oestrogen which are crucial to immunity, bone development, female reproduction, etc. can bind to transcriptional factors and release their inhibitor. Oestrogen crosses the plasma membrane freely as it is lipid-soluble.
- [<strong>⚙️ Most of a Cell's DNA is not Translated</strong>](https://thealevelbiologist.co.uk/most-of-a-cells-dna-is-not-translated/) - Stem cells, just like tree stems are to branches, are the common source of all different kinds of cells. Cells start out as stem cells, and totipotent (totally-powerful) cells can differentiate into any kind of cell. When they translate only certain parts of their DNA, they become specialised. Pluripotent (many-powerful) stem cells can differentiate into a wide variety of tissues, but not quite any…
- [<strong>Alteration of the sequence of bases in DNA can alter the structure of proteins</strong>](https://thealevelbiologist.co.uk/alteration-of-the-sequence-of-bases-in-dna-can-alter-the-structure-of-proteins/) - There are different types of mutation: 1. Deletion where one or more nucleotide bases are deleted. AGTCA becomes AGCA 2. Substitution where one or more nucleotide bases are replaced by others. AGTCA becomes AGTCG 3. Addition where one or more nucleotide bases are added as extra. AGTCA becomes ATGTCA 4. Inversion where a section of DNA is inverted e.g. AGTTCATTCCAGG becomes…
- [<strong>Gene Pools (Edexcel)</strong>](https://thealevelbiologist.co.uk/gene-pools/) - In the wild, each species may exist as one population or multiple populations. Different populations correspond to defined areas – habitats. The sum of all present alleles for a given gene in a given population is known as the gene pool.
- [<strong>Transfer of genetic information</strong>](https://thealevelbiologist.co.uk/transfer-or-genetic-information/) - Humans have 2 sets of chromosomes, so for each distinct chromosome e.g. chromosome 1, there are two copies. How do the same genes on both homologous chromosomes interact if they result in different phenotypes? Which has priority? If you crossed a green pea plant with a yellow pea plant, what colour would the offspring be? What about their offspring’s offspring…
- [<strong>Origins of genetic variation</strong>](https://thealevelbiologist.co.uk/origins-of-genetic-variation/) - Let’s look at 3 broad categories of source of genetic variation: mutation, meiosis and fertilisation. DNA mutation occurs spontaneously and creates a direct change in the genetic material. Single bases may be changed, added or removed, or even large chunks of chromosomes can be swapped between them or duplicated. Whole chromosomes, too, can shift around. Mutations are a random occurrence during DNA replication and the rate of mutation is influenced by external factors such as UV radiation. There are different types of mutation.
- [<strong>Investigating diversity</strong>](https://thealevelbiologist.co.uk/investigating-diversity/) - With advancing technology, scientists no longer have to rely on capturing animals or gathering data manually in the field. Bioinformatics enables the analysis of a whole genome from a computer. Once the initial DNA sequencing has taken place, a lot of research can be conducted just from that data. For example, the DNA, mRNA or amino acid sequence between two individuals or species can be compared.
- [<strong>Biodiversity within a community</strong>](https://thealevelbiologist.co.uk/biodiversity-within-a-community/) - It’s not hard to figure out the impact both have on species diversity. Deforestation practically removes many, whole trees, and with them goes the shelter and food source of many other organisms. A great reduction in species diversity can be expected as a result. Agriculture by humans results in a single dominant species which occupies vast land at the expense of others. Humans actively remove other species by the use of pesticides, insecticides and (indirectly)…
- [<strong>Species and taxonomy</strong>](https://thealevelbiologist.co.uk/genetic-information/species-and-taxonomy/) - What is courtship behaviour? The acts it encompasses are as varied as life itself; a sound, a gesture, an action, etc. A species is defined in terms of observable physical features as well as the ability to produce fertile offspring. This is a challenging task, as most species that have ever lived on this planet are now extinct, and many more alive today have yet to be discovered and classified.
- [<strong>Genetic diversity and adaptation</strong>](https://thealevelbiologist.co.uk/genetic-diversity-and-adaptation/) - The allele frequency in a population’s gene pool can change as a result of selection. The effectors of selection can be varied, yet the outcome is similar: advantageous or preferred alleles and the traits associated with them increase in frequency, while detrimental or disfavoured alleles result in a decreased frequency.
- [<strong>Genetic diversity can arise as a result of mutation or during meiosis</strong>](https://thealevelbiologist.co.uk/genetic-diversity-can-arise-as-a-result-of-mutation-or-during-meiosis/) - If 2 different triplet codes translate into the same amino acid, the polypeptide chain will remain unchanged. This of course only applies to substitutions. Another scenario where a mutation may cause no effect is if it arises in an intron. Mutations are a random occurrence during DNA replication and the rate of mutation is influenced by external factors such as UV radiation. There are different types of mutation.
- [<strong>DNA, genes and chromosomes</strong>](https://thealevelbiologist.co.uk/dna-genes-and-chromosomes/) - DNA and chromosomes may seem like completely separate things. Well, they’re not. In fact, all chromosomes are individual DNA molecules coiled and twisted around, because DNA is huge. At least in eukaryotes it is. That’s one of the first differences between eukaryotes and prokaryotes in their DNA – prokaryotes have less DNA.
- [<strong>Transport in plants (Edexcel)</strong>](https://thealevelbiologist.co.uk/transport-in-plants/) - What you can see above is a delicious slice of pineapple. OK, it’s not. That is a slice of a root. Roots, as you may have seen in real life, are hairy. All those tiny and not so tiny root hairs buried into the soil greatly increase the surface area of the root. This exposes it to more water molecules which can be taken up. The hairs are nothing like human hairs; they are extensions of the outer layer of the root, made up of cells. This layer is called the epidermis.
- [<strong>Transport of materials between the circulatory system and cells</strong>](https://thealevelbiologist.co.uk/transport-of-materials-between-the-circulatory-system-and-cells/) - Lymph is formed from the interstitial fluid found throughout tissue and is similar in composition to blood plasma, lacking red blood cells. The lymphatic system plays a role in circulating blood back to the heart as well as passing it though the lymph nodes to clear it of any infectious agents.
- [<strong>Transport of gases in the blood</strong>](https://thealevelbiologist.co.uk/transport-of-gases-in-the-blood/) - Carbon dioxide and oxygen are transported in the blood under different conditions. Carbon dioxide is more soluble than oxygen, so some of it is directly present in the blood plasma. It can also be present as bicarbonate ions which increase blood acidity and signal if there is too much CO2 in the blood and not enough O2. Finally, both CO2 and O2 can bind to haemoglobin which is present in red blood cells. Its function is the oxygenation of tissues, as oxygen is central to aerobic respiration, the metabolic process of creating chemical energy for all cell functions.
- [<strong>Cell transport mechanisms</strong>](https://thealevelbiologist.co.uk/gas-exchange/) - Since gas exchange occurs by diffusion alone, single-celled organisms such as bacteria do not need any specialised structures to achieve it for them. This is because, being so small, diffusion occurs readily as their surface area to volume ratio is high.
- [<strong>Cell transport mechanisms</strong>](https://thealevelbiologist.co.uk/cell-transport-mechanisms/) - Armed with this knowledge of lipids, as well as carbohydrates and proteins, we can now explore the structure of plasma membranes, specifically in the context of the fluid-mosaic model. Phospholipids have a hydrophilic (water loving) head, and hydrophobic (water repelling) tails. This results in the formation of a phospholipid bilayer (double layer), which forms the basis for the plasma membrane.
- [<strong>Surface area to volume ratio (Edexcel)</strong>](https://thealevelbiologist.co.uk/surface-area-to-volume-ratio/) - Organisms exchange substances and heat with their environment all the time, and this possibility is crucial to survival. The specific way in which this is achieved is very tightly related to the shape and structure of the specific organism, as well as its environment. For example, unicellular organisms are so small that molecules such as oxygen and water can readily diffuse in and out via the membrane, due to the short diffusion pathway. Could this be achieved by a human, or even a bee? No – they are simply too big.
- [<strong>Structure of bacteriophage and of HIV</strong>](https://thealevelbiologist.co.uk/structure-of-bacteriophage-and-of-hiv/) - In the presence of a larger organism of their specific fit (and there are viruses to target anything), they come alive by hijacking its life tools: nutrients, energy, ribosomes, you name it. They only carry the genetic information they need to invade and replicate. Invade and replicate. A bit of a glitch of life, or the perfect expression of it? Both DNA and RNA viruses make use of their host’s transcription and translation machinery such as ribosomes and…
- [⚙️ Lipids and amino acids in respiration](https://thealevelbiologist.co.uk/lipids-and-amino-acids-in-respiration/) - Emulsification is necessary because lipids are not water soluble. When they travel through the digestive tract from food, they maintain rather large aggregates of themselves. Emulsification is carried out by bile salts (in bile, produced by the liver and stored and concentrated in the gall bladder) which are amphipathic as they have both hydrophobic and hydrophilic parts.
- [<strong>Glycolysis and the Krebs cycle</strong>](https://thealevelbiologist.co.uk/glycolysis-and-the-krebs-cycle/) - Don’t make the mistake of associating plants with photosynthesis, and non-plants with respiration. They are different processes. Plants photosynthesise and respire at the same time, we eat plants and respire at the same time. Similarly, don’t confuse respiration with ventilation. In the context of biology, ventilation is the movement of air through our respiratory system i.e. breathing
- [Muscle contraction](https://thealevelbiologist.co.uk/muscle-contraction/) - The membrane is called sarcolemma while the cytoplasm is called sarcoplasm (it has a much higher glycogen storage content). The basic unit of muscle tissue is the myofibril which has a tube-like shape and is made up of the muscle cells themselves. These look fibrous and are organised into…
- [Mammalian vision](https://thealevelbiologist.co.uk/mammalian-vision/) - Having two eyes provides binocular vision which enhances depth perception, gives a wider visual field and better distance perception. The eye has many different components that work in unison to enable vision. On its surface and lining the eyelids, the conjunctiva secretes mucus and tears, lubricating the eye and providing immune surveillance via the many microvessels. The sclera is the white of the eye and contains collagen and elastic…
- [Synapse (CCEA)](https://thealevelbiologist.co.uk/synapse/) - A synapse is the site of communication between the end of an axon and the beginning on a dendrite. It can also be between a neuron and a non-neuron cell such as a muscle cell. In the olden days people used to think that there were no gaps between neurons, and they just extended continuously throughout the body (silly eh?). Now we know better, much better. More for you to learn!
- [Action potential](https://thealevelbiologist.co.uk/action-potential/) - According to these electrochemical gradients, Na+ ions should move back inside to balance out their concentration (equilibrate) while K+ ions should move back outside the membrane until the concentrations are equal inside and out. This clearly isn’t the case, so what gives? Found on the membrane there are Na+/K+ pumps which carry out active transport against the electrochemical gradient of these ions. The resting potential of the membrane is negative on the inside and positive on the outside – but how?
- [Neurones](https://thealevelbiologist.co.uk/coordination-and-control/neurones/) - This insulating sheath made up of Schwann cells is key in ensuring fast signal transmission. The signal is able to “jump” along the axon without losing its strength. Instead of the signal being gradually weakened by the resistance that an axon membrane exposed to the environment creates, this signal is shielded by the…
- [Plant hormones](https://thealevelbiologist.co.uk/plant-hormones/) - Auxin stimulates cell elongation in the roots and shoots in flowering plants. It accumulates away from light which simulates growth on the dark side, bending the shoot in the opposite direction, where the light is. This ensures plants respond to their environment in a way that best maximises their survival prospects. More light enables better photosynthesis, while growing upwards exposes their leaves to more sunlight. Auxin also suppresses lateral bud growth, so only the apical bud is growing, as it secretes auxin that travels downwards.
- [Stem Cells](https://thealevelbiologist.co.uk/stem-cells/) - Cells in our bodies have the same amount of DNA, and that DNA is completely identical! So how come a muscle cell and a brain cell both have very different structure and function despite that? How can cells be different to one another yet carry the same genetic information which codes for the same proteins? Indeed, how come most of a cell’s DNA is not translated?
- [Factors affecting gene expression](https://thealevelbiologist.co.uk/factors-affecting-gene-expression/) - The available genetic material in an individual or a species is one thing. All cells in the body have the same DNA. Forget that! (no, not really) That’s not the fun part. The fun part is how the genome works, and how genes are expressed, if at all. This is what actually keeps life ticking the way it does. This is why we have cells that look different and act differently. This is why your environment and choices can make a difference.
- [Using gene sequencing](https://thealevelbiologist.co.uk/using-gene-sequencing/) - The information gleaned from a virus proteome, for example, can inform vaccination targets by selecting appropriate antigens such as elements of the viral capsid. Other exciting synthetic biology applications can be explored such as glowing beer, synthesising specific compounds useful in medicine or manufacturing using organisms to whom that product isn’t native in an attempt to boost production or create new…
- [Populations in ecosystems (AQA)](https://thealevelbiologist.co.uk/populations-in-ecosystems/) - An ecosystem comprises the community of living organisms in a habitat, together with all the non-living components such as water, soil, temperature, etc. called abiotic factors. Why are different organisms of different species able to coexist in the same habitat? How come they don’t directly compete with one another and drive others out? Have a watch…
- [<strong>Evolution may lead to speciation</strong>](https://thealevelbiologist.co.uk/evolution-may-lead-to-speciation/) - Individuals within a population exhibit variety of phenotypical traits caused by both their alleles and the environment. Primarily the source of this variation is mutation. Secondarily it is meiosis and the random fertilisation of gametes in the case of sexual reproduction. The balance of survival and reproduction is affected by factors including predation, disease and competition. Some appearances and behaviour can attract more predators while others such as camouflage can…
- [The Hardy-Weinberg Principle (AQA)](https://thealevelbiologist.co.uk/the-hardy-weinberg-principle-2/) - In the wild, each species may exist as one population or multiple populations. Different populations correspond to defined areas – habitats. The sum of all present alleles for a given gene in a given population is known as the gene pool.
- [<strong>Critical evaluation of biological research</strong>](https://thealevelbiologist.co.uk/investigative-biology/critical-evaluation-of-biological-research/) - Fun, fun, fun! Biological research is presented in roughly the following format: title, abstract (summary), introduction, methods, results, discussion (+ conclusion, references, other notes, appendices if applicable). Citations should be present throughout as necessary. It’s useful to actually be involved in the experimentation, analysis of data and writing of these papers in order to understand how they are written, why and for whom.
- [Experimentation](https://thealevelbiologist.co.uk/experimentation/) - Pilot studies are mini-versions of what is to be the main experiment. It can help test out the environment or variables and try to fine tune the final experimental design. Pilot studies are useful as part of very large experiments that cannot afford to make silly errors. They can also provide some insight when a full-scale experiment would be too complex or costly.
- [Scientific principles and process](https://thealevelbiologist.co.uk/investigative-biology/scientific-principles-and-process/) - Science provides models for harnessing knowledge in a relatively objective, material and quantified environment. It involves high levels of reproducibility and peer-to-peer confirmation of findings, and as such can produce very widely applicable and powerful knowledge. The downside to this is that due to its basis of formulating testable hypotheses, many types of knowledge remain outside of the working field of science.
- [<strong>☠️ Threats to biodiversity</strong>](https://thealevelbiologist.co.uk/sustainability-interdependence/threats-to-biodiversity/) - As populations of certain species become smaller, for example due to overfishing, their genetic diversity shrinks, and inbreeding predisposes them to deleterious phenotypes. There is a threshold for how low a population can get before it can no longer be saved from extinction. This differs between species, and there are species which are inherently of low genetic diversity without having problems.
- [<strong>Mass extinction and biodiversity</strong>](https://thealevelbiologist.co.uk/mass-extinction-and-biodiversity/) - Extinction events are defined by periods of great loss of biodiversity. Fossil evidence has pointed to several mass extinctions from multiple causes including the great oxygenation event following the evolution of pant photosynthesis, environmental effects caused by forces outside the Earth, and indeed the expansion of human populations.
- [<strong>Social behaviour</strong>](https://thealevelbiologist.co.uk/sustainability-interdependence/social-behaviour/) - Primates including humans live in societies where individuals sustain relationships, whether emotional or utilitarian, in order to accomplish functions that would otherwise be impossible. Participation is such groups that can be very complex requires advanced learning methods in order to be able to perceive oneself and others in these relationships.
- [<strong>Symbiosis</strong>](https://thealevelbiologist.co.uk/symbiosis/) - Symbiosis is defined as the co-evolved intimate relationship between members of different species. It comes in many flavours, including the one-sided and abusive parasitic relationship and the more reasonable mutualism where both parties benefit from the relationship. A third type, commensalism, is a relationship where one species benefits from the other one-sidedly, but without harming it.
- [<strong>Animal welfare</strong>](https://thealevelbiologist.co.uk/sustainability-interdependence/animal-welfare/)
- [<strong>Crop protection</strong>](https://thealevelbiologist.co.uk/crop-protection/)
- [<strong>Plant and animal breeding</strong>](https://thealevelbiologist.co.uk/sustainability-interdependence/plant-and-animal-breeding/)
- [<strong>Food supply, plant growth and productivity</strong>](https://thealevelbiologist.co.uk/food-supply-plant-growth-and-productivity/)
- [<strong>Mass transport in plants</strong>](https://thealevelbiologist.co.uk/mass-transport-in-plants/) - The cell sap (i.e. cell juice) has a lower water potential than the fluid found in the soil, so the water in the soil kindly makes its way into the thirsty awaiting root. Once the water reaches the first cell in its path, the water potential of that cell is increased compared to the cell next to it. Therefore, water moves into the next cell, leaving the current cell. All those tiny and not so tiny root hairs buried into the soil greatly increase the surface area of the root. This exposes it to more water molecules which can be taken up.
- [<strong>Mass transport in animals</strong>](https://thealevelbiologist.co.uk/mass-transport-in-animals/) - They would form like a… circulatory system. Oh wait, that’s precisely what mammals have: a circulatory system made of arteries, veins, capillaries, etc. Gas exchange in large multicellular organisms is achieved by organs which have a large surface area and so are able to successfully provide the substances the organism needs in order to survive. In humans this is achieved by the lungs.
- [<strong>Digestion and absorption</strong>](https://thealevelbiologist.co.uk/digestion-and-absorption/) - Digestion is the process by which large biological molecules such as carbohydrates, lipids and proteins get hydrolysed into their smaller constituent molecules so they may be absorbed across cell membranes. Digestion starts with food ingestion and even before the nutrients reach the stomach. A variety of enzymes carry out the breakdown of these nutrient molecules. The first, amylase, is present in saliva as well as secreted by the pancreas.
- [☁️ Gas exchange (Edexcel)](https://thealevelbiologist.co.uk/gas-exchange-2/) - Gas exchange is central to life. Oxygen is needed in respiration* which generates usable energy without which life wouldn’t exist. Removing the resulting carbon dioxide is crucial too. Water can be a gas too, in the form of water vapour. This may in certain organisms escape with the air, so water preservation versus gas exchange is always an important thing to bear in mind. This is especially important when talking about insects and plants.
- [<strong>Size and Surface Area</strong>](https://thealevelbiologist.co.uk/size-and-surface-area/) - The volume is what determines the amount of substances which need exchanging, while the surface area determines the amount which can be exchanged. Key principle: as the size of an organism increases, the surface area to volume ratio decreases. That might seem hard to really understand. Why use a ratio in the first place? Well, the ratio shows the relationship between surface area and…
- [Proteins as infectious agents](https://thealevelbiologist.co.uk/proteins-as-infectious-agents/) - It is strange to think of proteins as infectious agents. More commonly, viruses, bacteria and parasites are thought of as infectious agents. They invade their host, use up its resources and damage it in the process, in order to propagate themselves.
- [Outline of the plant and animal kingdoms](https://thealevelbiologist.co.uk/outline-of-the-plant-and-animal-kingdoms/) - The plant kingdom Plantae comprises of mosses, liverworts, ferns, conifers and flowering plants. Despite their popularity, flowers are actually very new relative to other plants.
- [Gas exchange in fish](https://thealevelbiologist.co.uk/gas-exchange-in-fish/) - Fish extract dissolved oxygen molecules from the surrounding water. The oxygen content of water is much lower compared to air, so fish have special adaptations which enable them to make the most of the available oxygen. These adaptations are gills.
- [Family trees (pedigree)](https://thealevelbiologist.co.uk/family-trees-pedigree/) - This type of diagram shows genetic inheritance over generations. Squares are males and circles are females. Filled shapes are affected by the specified condition while hollow shapes are not.
- [Down’s syndrome, Turner’s syndrome and Klinefelter’s syndrome](https://thealevelbiologist.co.uk/downs-syndrome-turners-syndrome-and-klinefelters-syndrome/) - During meiosis, different chromosome distribution in the gametes can occur which can leave them without the expected number of chromosomes. If there are more chromosomes than expected (2 of each in humans), this is termed polysomy and can result in conditions such as Down’s syndrome. If there are fewer chromosomes than expected, it is monosomy and can result in conditions such as Turner’s syndrome.
- [Primates](https://thealevelbiologist.co.uk/primates-2/) - Primates is an order that belongs to the mammalian class. It is also the order that humans (Homo sapiens) are part of. Primates evolved to live in the trees of tropical forests, which was a challenging niche to adapt to.
- [Neural development](https://thealevelbiologist.co.uk/neural-development/) - Brain development takes place significantly in the first part of life, and before birth. As a large and energy-hungry organ, its development starts from a simple location at the end of the nerve cord in the early embryo, to a highly complex structure with multiple areas, as neurons are synthesised in a stem cell rich part of the brain before migrating to their respective final locations.
- [Functions of the liver](https://thealevelbiologist.co.uk/functions-of-the-liver/) - The liver performs hundreds of functions in the body such as detoxifying the blood, red blood cell homeostasis and hormone secretion. It is capable of regenerating its function but not its form, and processes the many biochemical reactions required for the whole body, acting as an assistant to digestion, processing carbohydrates, lipids and a central processor of proteins.
- [Environmental protection](https://thealevelbiologist.co.uk/environmental-protection/) - Microorganisms can be used to recover ecosystems when environmental disasters such as oil spills occur. Oil spills pollute oceans, rivers and their ecosystems because they are very dense, toxic and difficult to break down or fit into the existing ecosystem.
- [Deforestation](https://thealevelbiologist.co.uk/deforestation/) - Deforestation for land space for human uses, wood or oil, such as the extensive deforestation in the Amazon, has led to both extinction concerns by the removal of animals’ habitats, as well as the challenge of balancing human production needs with conservation needs.
- [Biomes](https://thealevelbiologist.co.uk/biomes/) - A biome is a wider habitat where the environmental influences lead to similar kinds of organisms that inhabit them. Some parts of the world are deserts, some have tall trees and others only have grasses. While geographically they are not connected (such as deserts on different continents), they are separately similar. This is reflected in their plants, animals and niches.
- [Gene cloning](https://thealevelbiologist.co.uk/gene-cloning/) - This special case of DNA is called complementary DNA – cDNA. cDNA via reverse transcriptase: AGGTACGGTAAACCC (remember that DNA unlike mRNA is double-stranded; not shown for simplicity). If we wanted the portion after the second G above, is there a way we could cut the DNA? It appears so. Some microorganisms have actually evolved enzymes whose job it is to invade a host and chop its DNA up at specific sequences.
- [DNA probes, microarrays and genetic fingerprinting](https://thealevelbiologist.co.uk/microarrays-and-genetic-fingerprinting/) - Techniques used to identify gene location for a variety of purposes include DNA hybridisation and DNA probes. These involve tagging a DNA strand with a fluorescent agent and binding it to a new strand, the probe, which is complementary to the target gene. The new double-stranded DNA is a hybrid. The extent of binding to the probe (and hence the complementarity between base pairs) is measured by the intensity of fluorescence seen under UV light. This technique can be used to reveal the presence of heritable conditions, drug responses or health risks. You can get this done today!
- [Polymerase chain reaction (PCR)](https://thealevelbiologist.co.uk/polymerase-chain-reaction-pcr/) - If we have obtained a DNA sample or a few, what next? Well, nothing much can be done with that. We must obtain exponentially more DNA to use for any purpose. And it all of course must be identical. We must essentially clone our DNA. Considered the very staple of molecular biology, this technique for multiplying DNA many-fold was invented by a chap Kary Mullis who believes in astrology.
- [Epigenetics ](https://thealevelbiologist.co.uk/epigenetics/) - In eukaryotes, epigenetics refers to the heritable changes in gene function that do not involve any change to the DNA sequence. This underpins an embryo’s ability to differentiate its cells into specialised lineages for different organs and tissues in the adult: skin tissue, muscle tissue, nervous tissue, etc.
- [Polypeptide Synthesis](https://thealevelbiologist.co.uk/polypeptide-synthesis/) - Proteins are made up of amino acids linked by peptide bonds, therefore a protein may be referred to as a polypeptide (of course, some proteins such as haemoglobin have extra bits to them). All are encoded for by the information stored in DNA. Let’s see how exactly this happens.
- [The Genetic Code](https://thealevelbiologist.co.uk/the-genetic-code/) - DNA is a large molecule made up of variable bases (adenine, thymine, cytosine, guanine). The precise sequence and location of these bases determines what structure a second molecule, mRNA (messenger RNA) has once it’s “read” the template DNA. In turn, the sequence and location of mRNA bases determines what amino acids will be chosen in the assembly of a given protein that the original DNA encoded for, once it reaches a ribosome and is constructed by tRNA (transfer RNA).
- [Courtship behaviour and sexual selection](https://thealevelbiologist.co.uk/option-b-neurobiology-behviour/courtship-behaviour-and-sexual-selection/) - Courtship behaviours also allow organisms to approach one another without aggression or invasion of their personal space. Sometimes the outcome of courtship behaviour is the formation of a pair bond. This bond results in a better reproductive success, due to the increased survival probability of the offspring. In some species this is the case, while in others it isn’t. This is tightly related to a specific organism’s physiology…
- [Dominance hierarchies in vertebrates](https://thealevelbiologist.co.uk/option-b-neurobiology-behviour/dominance-hierarchies-in-vertebrates/) - Dominance hierarchies in vertebrates emerge as individuals in social groups attempt to find their place relative to others in the group. Pecking orders are established in groups where each individual is ascribed a rank relative to the others. Challenges between individuals that result in the determination of their relative positions help to prevent a confrontation each time they meet. On the ends of the spectrum of social hierarchy there is egalitarianism on one end, where all individual members are of the same rank, and despotism on the other end, where one individual is dominant over all the others who are submissive.
- [Insect social structure](https://thealevelbiologist.co.uk/option-b-neurobiology-behviour/insect-social-structure/) - Some insects, notably ants and some bees, display the highest level of organisation in their social structure. This structure is called eusociality and it involves a population whose individuals are reproductive or non-reproductive, and undertake different roles based on a caste system. There may be a queen and a king who are solely reproductive, such as in termites. The rest of the population are sterile workers whose job it is to provide food by foraging and other tasks, as well as individuals tasked with defence of the colony. The roles are so strongly established, that the huge jaws of the defensive termites prevent them from being able to feed themselves.
- [Social groups](https://thealevelbiologist.co.uk/option-b-neurobiology-behviour/social-groups/) - Primates including humans live in societies where individuals sustain relationships, whether emotional or utilitarian, in order to accomplish functions that would otherwise be impossible. Participation is such groups that can be very complex requires advanced learning methods in order to be able to perceive oneself and others in these relationships. Some of the behaviours emerging from this learning are imitation and insight. Imitation involves observing the actions of another and mimicking them. Insight is an understanding of a cause and effect in a given situation. This gorilla is playing on a Nintendo DS.
- [Biodiversity (Edexcel)](https://thealevelbiologist.co.uk/edexcel-classification-biodiversity/biodiversity/) - It doesn’t take a complex formula to figure out that community #1 is far more diverse compared to community #2, despite them having the same number of species and individuals. The distribution of individuals to species is important in determining a community’s diversity.
- [Natural selection](https://thealevelbiologist.co.uk/natural-selection/) - The allele frequency in a population’s gene pool can change as a result of selection. The effectors of selection can be varied, yet the outcome is similar. This is essentially a way of thinking about all the individuals in a population contributing their alleles towards the overall allele frequency. The sum of all present alleles for a given gene in a given population is known as the gene pool.
- [Classification](https://thealevelbiologist.co.uk/edexcel-classification-biodiversity/classification/) - In the old days, a species was known as a collection of individuals similar enough in resemblance to be put in the same box. This was purely based on physical features. Today we know that similar physical characteristics on their own aren’t enough to define a species. A species is defined in terms of observable physical features as well as the ability to produce… Taxonomy refers to the classification of living things by giving unique names to each species, and creating a hierarchy based on evolutionary descent.
- [Respiratory diseases and treatment](https://thealevelbiologist.co.uk/respiratory-diseases-and-treatment/) - Pollutants such as those found in tobacco smoke, asbestos, and fungal spores can adversely impact on the respiratory system by causing short-term and long-term damage. Asbestos was a building material whose disturbed, fine particles lodged themselves in the lungs upon inhalation, and caused damage over time. Symptoms only occurred many years or decades after exposure.
- [The cellular basis of cancer and treatment](https://thealevelbiologist.co.uk/the-cellular-basis-of-cancer-and-treatment/) - Apart from specific, easily identifiable pathogens such as bacteria or viruses which can cause disease, another major cause of disease is lifestyle. Lifestyle includes the choices that we make in regards to our food, drink, whether we smoke or use drugs, certain jobs we do, even the place where we live. The way we can measure the impact of certain lifestyle choices is by knowing risk factors. Certain diseases like cancer and coronary heart disease are associated with certain risk factors, such as smoking and obesity. On the flip side, changes in lifestyle are also associated with a decrease in risk of contracting these diseases.
- [⚔️ Controlling communicable diseases](https://thealevelbiologist.co.uk/controlling-communicable-diseases/) - Vaccinations prevent symptoms of an illness (such as flu or rubella) from developing, by creating a primary immune response to an unharmful substance that the body identifies as a pathogen. This could be an antigen, or the pathogen itself – dead or otherwise modified to prevent disease. Some vaccines are really successful and have prevented many diseases so far, yet the flu vaccine remains a challenge due to the above points. The virus changes its antigens, and there is great variation to start off with.
- [The immune system (OCR)](https://thealevelbiologist.co.uk/the-immune-system/) - Immunity against invading pathogens is a crucial part of maintaining health. The body has adaptations which prevent invasion by pathogens, as well as processes in place to deal with those that manage to penetrate the body’s primary defenses. The skin and mucous membranes (e.g. mouth) are examples of such defenses. Sweat contains lysozyme which is an enzyme that breaks down bacterial walls. Stomach acid also destroys microorganisms that are ingested.
- [Pathogenic microorganisms](https://thealevelbiologist.co.uk/pathogenic-microorganisms/) - There are multiple ways in which pathogens cause disease. Bacteria can produce toxins, viruses take over cellular machinery such as enzymes and nutrients and destroy the cells in the process, while fungi can secrete enzymes that break down host tissue. There are many different kinds of bacterial toxin e.g. by Staph. aureus, such as protein barrels that integrate into the plasma membrane of host cells and cause their contents to leak out through these huge pores created by the…
- [The development of species: evolution and classification](https://thealevelbiologist.co.uk/cell-division-development-disease-control/the-development-of-species-evolution-and-classification/) - In order to achieve the above, though, we need a definition for both species and hierarchy. In the old days, a species was known as a collection of individuals similar enough in resemblance to be put in the same box. This was purely based on physical features. Today we know that similar physical characteristics on their own aren’t enough to define a species.
- [The developing individual: meiosis, growth and development](https://thealevelbiologist.co.uk/the-developing-individual-meiosis-growth-and-development/) - Gametes are genetically unlike one another – while cells in other tissues such as muscle or blood must be genetically identical to one another (clones), the very basis of sexual reproduction is genetic diversity. Meiosis is a type of cell division which results in 4 cells that are genetically non-identical from one parent cell. In order for once cell to divide to result in 4 cells, how many divisions must take place?
- [The developing cell: cell division and cell differentiation](https://thealevelbiologist.co.uk/the-developing-cell-cell-division-and-cell-differentiation/) - They’re made of a special protein called tubulin because they’re tubeeeeeeeeeeeees. Why didn’t they call it spaghettulin? I guess spaghetti aren’t hollow but… Microtubules also play a key part in how cell organelles are moved and placed within the cell. Two associated centrioles form the centrosome. The microtubules are also where spindle fibres extend from when they…
- [Fertilisers](https://thealevelbiologist.co.uk/fertilisers/) - Nitrogen and magnesium are inorganic nutrients used in fertilisers in some areas to support plant growth. Nitrogen is amongst some of the main elements that are supplemented via fertilisers, alongside potassium and phosphate. Magnesium is considered a trace element rather than a main element. Plant metabolism, with a key focus on photosynthesis, underlies the use of these fertilisers.
- [Limiting factors in photosynthesis](https://thealevelbiologist.co.uk/limiting-factors-in-photosynthesis/) - Photosynthesis, just like all other physiological processes in living things as well as chemicals and beyond, is subject to external influences. The main factors that weigh in on the efficiency and speed of photosynthesis are: 1. Temperature 2. CO2 Concentration 3. Light intensity. Both the concentration of carbon dioxide and the intensity of light are similar in that they are both direct ingredients in the overall photosynthesis reaction. But since temperature insists on…
- [Light-independent Reaction](https://thealevelbiologist.co.uk/light-independent-reaction/) - The light-independent reaction of photosynthesis is where the ultimate product, glucose, is made. Given its name, the reactions involved in this step do not require light, since the reactants used are taken from the products of the light-dependent reaction. The LIR occurs in the stroma of chloroplasts (the space around thylakoid stacks which contains lots of enzymes involved in photosynthesis).
- [Light-dependent Reaction](https://thealevelbiologist.co.uk/light-dependent-reaction/) - The electrons present in the chlorophyll of the plant’s chloroplasts are brought to a higher energy level (they enjoy dancing more) by light energy. This takes place on the thylakoid membrane, and more specifically in a conglomerate of proteins/enzymes dedicated to this reaction, called photosystem II. It’s known as photoionisation
- [Immobilised enzymes in biotech](https://thealevelbiologist.co.uk/immobilised-enzymes-in-biotech/) - Since enzymes are so specific, powerful – many thousands of times faster than some chemical catalysts – and operate at much lower temperatures, too, they are employed in many industries including food and cleaning. These industries work with tremendous amounts of product, so the amount of enzyme used for each reaction would be equally huge and very uneconomical, as enzymes can be expensive to make. Imagine adding a lot of precious enzymes to a giant processor of, say, baby food or detergent. You’d like to reuse the expensive enzymes, but you can’t extract the enzyme back from the giant processor full of stuff.
- [Enzyme Function](https://thealevelbiologist.co.uk/enzyme-function/) - Enzymes are proteins, so have a delicate tertiary structure that enables that enzyme’s adequate function. High temperature or pH would alter its tertiary structure. Inhibitors would bind to its active site, preventing substrates from doing so. This results in no enzyme-substrate complexes being formed. Let’s have a closer look at these properties individually.
- [Enzyme Structure](https://thealevelbiologist.co.uk/enzyme-structure/) - This can be described by the lock and key, and induced fit models of enzyme action. The lock and key model is based on complementary shapes between the enzyme and substrate. The substrate fits into the enzyme. The induced fit model: (the enzyme changes shape to “hug” the…
- [Organisation under the microscope: cells, tissues, organs](https://thealevelbiologist.co.uk/organisation-under-the-microscope-cells-tissues-organs/) - For anyone who’s seen the film Life starring our first Martian life form called Calvin, there is way that cells can associate the way Calvin does. In this case, cells aren’t at all differentiated to do different things in tissues, organs, etc. but instead maintain their single cell status among equal single cells. They associate at a higher level to produce certain greater effects, and can even look as if the structure were multicellular or complex, but it isn’t really, or at least it isn’t in the same way it is for true multicellular organisms.
- [Cell differences and microscopy](https://thealevelbiologist.co.uk/cell-structure-organisation/cell-differences-and-microscopy/) - You will need to know about the difference between light, transmission electron and scanning electron microscopes – LM, TEM and SEM. Both the latter (as the name suggests) use a beam of electrons, rather than light, to produce an image of the sample. TEM uses electrons which pass through the sample, so the resulting micrograph (image) shows everything within the sample in black and white, for example organelles in a cell. SEM uses electrons which scan the sample in 3D, resulting in a coloured micrograph with 3D detail, but no components from…
- [Prokaryotic Cells and Viruses](https://thealevelbiologist.co.uk/prokaryotic-cells-and-viruses/) - Prokaryotes do not have a nucleus like eukaryotes do. Their DNA is not membrane-bound, just free in the cytoplasm. The extra features of prokaryotic cells vs. eukaryotic cells you must learn are: -the cytoplasm overall does not contain membrane-bound organelles such as mitochondria and endoplasmic reticulum
- [⚙️ Eukaryotic Cells](https://thealevelbiologist.co.uk/eukaryotic-cells/) - The ones you must know about are: 1. Centriole 2. Nucleus 3. Mitochondria 4. Chloroplasts (plants and algae) 5. Golgi apparatus and Golgi vesicles 6. Lysosomes 7. Ribosomes 8. Rough endoplasmic reticulum and smooth endoplasmic reticulum 9. Cell wall and plasmodesmata (plants, algae, fungi) 10. Cell…
- [Transplantation and immunosuppression](https://thealevelbiologist.co.uk/transplantation-and-immunosuppression/) - Organ transplantation between individuals, such as kidney transplants, expose the recipient to the foreign antigens of the donor. Upon identifying the foreign antigens, the recipient’s immune response mounts a defence via production of specific B- and T-cells, attacking and damaging the new organ.
- [⚔️ Principles of immunity (CCEA)](https://thealevelbiologist.co.uk/principles-of-immunity/) - The specific immune response is split into humoral immunity and cell-mediated immunity. Humoral is to do with the blood and antibodies. Distinguishing between an antigen and an antibody is very important. Antigen = protein or carbohydrate foreign (not normally present) to a host’s organism Antibody = protein made as a response to detecting an antigen which binds to the antigen and prevents the pathogen from harming the…
- [Control of blood water potential](https://thealevelbiologist.co.uk/control-of-blood-water-potential/) - There are systems in place that keep the blood at the right composition and pressure. The hypothalamus and posterior pituitary in the brain release a hormone into the blood that reaches the kidney and enables its cells to take up more water, to prevent it being wasted in urine as the case may be. The hormone is known as vasopressin or antidiuretic hormone (ADH), has a very short half life of 16-24 minutes as you can imagine since it regulates fast-changing things like water retention and…
- [Control of Blood Glucose Concentration](https://thealevelbiologist.co.uk/control-of-blood-glucose-concentration/) - The pancreas has alpha and beta cells. Alpha cells secrete glucagon which increases blood glucose concentration, while beta cells secrete insulin which decreases blood glucose concentration. People with type 1 diabetes have destroyed beta cells, so their lack of insulin makes them have to take it via injections.
- [⚖️ Principles of homeostasis and negative feedback (AQA)](https://thealevelbiologist.co.uk/principles-of-homeostasis-and-negative-feedback/) - Why, though, is it so important to keep a strict temperature and pH? From a physiological viewpoint, think of enzyme activity. Its sensitivity to both temperature and pH means that the only conditions of optimal function will be strictly defined. Lots of enzymes denature past 40°C and are inactivated below…
- [Skeletal muscles are stimulated to contract by nerves and act as effectors](https://thealevelbiologist.co.uk/skeletal-muscles-are-stimulated-to-contract-by-nerves-and-act-as-effectors/) - The muscle is attached to the bone (spot the nice bone marrow) by the tendon. Muscle cells have a plasma membrane and cytoplasm much like any other cells, but each has a special name. The membrane is called sarcolemma while the cytoplasm is called sarcoplasm (it has a much higher glycogen storage content).
- [Synaptic Transmission](https://thealevelbiologist.co.uk/synaptic-transmission/) - A synapse is the site of communication between the end of an axon and the beginning on a dendrite. It can also be between a neuron and a non-neuron cell such as a muscle cell. In the olden days people used to think that there were no gaps between neurons, and they just extended continuously throughout the body (silly eh?). Now we know better, much better. More for you to learn!
- [Nerve Impulses](https://thealevelbiologist.co.uk/nerve-impulses/) - Labelled “insulating sheath”, the myelin sheath is responsible for protecting the electrical impulses that run across the neurone. But first, what happens in a resting state where no impulses are being sent? This is the resting potential where the membrane permeability differentiates between sodium (Na+) and potassium (K+) ions so that at any given time there are more Na+ ions outside than inside and more K+ ions inside than outside.
- [Control of Heart Rate](https://thealevelbiologist.co.uk/control-of-heart-rate/) - The hormone that increases heart rate is noradrenaline. This can be released by the brain’s medulla via the sympathetic neurons when baroreceptors which sense low blood pressure or chemoreceptors which sense excess or a lack of certain chemicals send signals via sensory neurons.
- [☝️Receptors](https://thealevelbiologist.co.uk/receptors/) - Named by its Italian discoverer Filippo Pacini (si splendido uomo!*), it is a 1 mm diameter skin receptor which enables us to perceive pressure and vibration. This is the receptor responsible for our awareness off smooth vs rough surfaces, shallow vs intense tactile sensation, etc. How does this seemingly magical process take place?
- [☀️ Survival and response (AQA)](https://thealevelbiologist.co.uk/organisms-respond/survival-and-response/) - The direct stimuli which contribute to plant survival (such as light, nutrients, gravity) are responded to by positive or negative tropisms. Tropisms get their names based on the stimulus they refer to. For example, a plant responding towards light would exhibit a positive phototropism. Most plants also exhibit negative gravitropism which means they grow away from…
- [Response to infection](https://thealevelbiologist.co.uk/response-to-infection/) - Different cells have different molecules presented on their surface to the immune system. These are often protein-based and enable the identification of: -pathogens -cells from other organisms of the same species -abnormal body cells -toxins
- [Problems of controlling endemic diseases](https://thealevelbiologist.co.uk/problems-of-controlling-endemic-diseases/) - Malaria is endemic to a wide stretch around the equator that covers South and Central America, Africa, the Middle East and South-East Asia. A disease is endemic when it occurs routinely in an area. An epidemic, on the other hand, is a temporary explosion of cases of a disease in an area.
- [Other pathogenic agents](https://thealevelbiologist.co.uk/other-pathogenic-agents/) - Bacteria are nowhere near the only agents of disease of biological origin. We’re talking parasites (protozoa), viruses and fungi for starters. Fungi are very different from bacteria, they’re eukaryotic! They’re also more closely related to animals than plants. Viruses, as previously covered, aren’t cells nor alive. Protozoa are (also eukaryotic) single-celled organisms. So without further ado, let’s see what the transmission, mode of infection and pathogenic effect are in stem rust fungus on cereal crops, common flu and malaria.
- [Antibiotic Resistance](https://thealevelbiologist.co.uk/antibiotic-resistance/) - The use of antibiotics is a common example of how evolutionary arms races are critical in the development and deployment of medicines that target organisms. As long as some individuals in a targeted population are able to survive the antibiotic, or in time can develop resistance, under the selection pressure of antibiotic use an ever increasing resistant population will emerge.
- [☠️ Antibiotics (WJEC)](https://thealevelbiologist.co.uk/antibiotics/) - They are substances which occur both naturally, as well as artificially as made by humans. The reason they are so widespread and important is because they solve a problem humanity has had for a very long time (i.e. forever). They are used to treat bacterial infections. Today that might seem like a small thing, yet around the globe millions of people still die all the time due to bacterial infections (e.g. pneumonia). It’s not a small thing, it is one of the greatest medical discoveries.
- [Bacteria as pathogens](https://thealevelbiologist.co.uk/bacteria-as-pathogens/) - Bacteria can cause disease (become pathogenic) when they invade the interface between an organism and their environment. This could be the skin, lungs, digestive system, etc. There are two ways which you need to know about in which pathogens cause disease: 1) damage to the cells, and 2) producing toxins.
- [Microbial Techniques](https://thealevelbiologist.co.uk/microbial-techniques/) - Aseptic means free of contamination. There are hundreds of fungal spores in the air we breathe at all times. There are bacteria and viruses everywhere. If we are to culture Escherichia coli (bacteria, prokaryote) or perhaps Pichia pastoris (yeast, eukaryote), we’re going to be feeding them some nice nutrients, and chances are, loads of other microorganisms will jump at the opportunity to feast.
- [Parasitism (Scottish Advanced Higher)](https://thealevelbiologist.co.uk/parasitism/) - Parasites are symbiotic species that rely on their host for nutrients, like predators rely on prey. This is at the expense of the host, which often suffers illness as a result, or a damaged reproductive function. Unlike predators that have a lower reproductive capacity compared to their prey, parasites have a higher reproductive potential than their host.
- [Sex and behaviour](https://thealevelbiologist.co.uk/sex-and-behaviour/) - Parental investment refers to the input required by parents to ensure the survival of their offspring. This can be diverged even before the offspring are brought to life, in terms of the preparations required, whether biological or environmental. For example, the production and incubation of eggs requires more investment of energy for fewer offspring, while the production of sperm cells requires less energy for more cells.
- [Variation and sexual reproduction](https://thealevelbiologist.co.uk/organisms-evolution/variation-and-sexual-reproduction/) - Sexual reproduction has a few disadvantages compared to asexual reproduction. It requires more than just one individual to parent each offspring, rendering about half of the individuals unable to carry through the bearing of offspring, while allowing just half of each parent’s contribution to be inherited by their offspring. The advantage that makes it significant enough to outweigh the disadvantages is increased diversity. With each generation, diversity is inevitably inscribed into offspring, and the sources of genetic variation maximised with each cross.
- [Organisms](https://thealevelbiologist.co.uk/organisms-evolution/organisms/) - What a subtopic title indeed – organisms! I didn’t even make it up myself, it’s the spec. This topic is really about evolution. The basics of evolution, such as mutation, genetic drift, natural and sexual selection and allele frequency are covered in the Scottish Higher topics Evolution and Mutations, so this topic builds further on those concepts. Previously we learned that evolution is the change in heritable traits through generations, brought about by random shifts such as genetic drift, as well as directed shifts such as selection.
- [Field techniques for biologists](https://thealevelbiologist.co.uk/organisms-evolution/field-techniques-for-biologists/) - Health and safety in carrying out field work is key. While hazards in the lab might extend to toxic chemicals and disposing of GM microorganisms, hazards in the field can be even more diverse. Terrain, weather conditions and isolation can all play into this, depending on location. It only takes a brief look at wild animal documentaries to see how venturing out into nature can pose many hazards.
- [Kidney functions and malfunctions](https://thealevelbiologist.co.uk/genetics-control-homestasis/kidney-functions-and-malfunctions/) - Osmoregulation refers to the control of water potential of the blood. The blood is complicated, it has all these ions and proteins and stuff. Cells use various things up all the time and some more often than others at different times, night, day, sweat, tears, etc. Molecules undergo deamination in the liver. This means they have an amino group removed. Since these amino group form ammonia which is toxic, it must be converted to safe urea in the blood before being excreted in urine by the kidneys. This is accomplished through the reaction with…
- [The hormonal control of blood glucose and the management of diabetes](https://thealevelbiologist.co.uk/genetics-control-homestasis/the-hormonal-control-of-blood-glucose-and-the-management-of-diabetes/) - The liver and the pancreas have a central role in the regulation of blood glucose concentration. The cells in the pancreas secrete the hormones which tell cells to take up glucose from the blood or not take it up. On demand, glucose is made from broken down glycogen in the liver.
- [⚖️ The principles and importance of homeostasis](https://thealevelbiologist.co.uk/genetics-control-homestasis/the-principles-and-importance-of-homeostasis/) - If an oven is set at 220°C, both a decrease and an increase in temperature is a deviation. So if the temperature drops or rises, a sensor picks that up and commands the heater to turn on or off. Welcome to homeostasis – the maintenance of physiological parameters within optimal range. Other parameters include blood pressure and pH. The internal environment of our bodies is constantly kept within strict limits. Take for example temperature.
- [The effect of ageing on the nervous system](https://thealevelbiologist.co.uk/genetics-control-homestasis/the-effect-of-ageing-on-the-nervous-system/) - Alzheimer’s disease is the most prevalent type of dementia. Dementia is a disease affecting the brain, caused by an interplay of genetic and environmental factors over time. Age is the main risk factor for developing Alzheimer’s disease. Neurons die gradually as Alzheimer’s disease progresses over several years, due to buildups of otherwise safe proteins including amyloid and tau. Amyloid forms plaques between neurons while tau forms tangles inside them. These structures result in the death of brain cells.
- [Monitoring visual function](https://thealevelbiologist.co.uk/genetics-control-homestasis/monitoring-visual-function/) - The eyeball is a magnificent contraption of brain tissue that protrudes during development to form said ball. It works to capture and process photons in light, and transmit the compressed information via the optic nerve to the visual cortex in the brain. This journey starts in the retina, which is the innermost layer at the back of the eye containing the light receptors and cells involved in this process.
- [The nervous system and the identification and consequences of damage](https://thealevelbiologist.co.uk/genetics-control-homestasis/the-nervous-system-and-the-identification-and-consequences-of-damage/) - The nervous system coordinates bodily functions via chemical and electrical signals. It processes information throughout the body by carrying signals between the central nervous system (CNS) and peripheral nervous system (PNS). The CNS is composed of the brain and spinal cord, while the PNS consists of nerves which are connected to the CNS and reach the rest of the body.
- [Gene technologies (OCR)](https://thealevelbiologist.co.uk/genetics-control-homestasis/gene-technologies/) - As previously covered, mRNA is messenger RNA i.e. the molecule that takes the genetic information encoded by DNA (transcription) and brings it to the ribosome to initiate translation of the code into a polypeptide. The production of mRNA in human cells is not a simple transcription of DNA, as previously seen. The pre-mRNA is the simple transcript of DNA, but the mature mRNA has to be spliced first, as well as go through a couple of post transcriptional edits before being ready for translation at the ribosome site.
- [Population genetics and epigenetics](https://thealevelbiologist.co.uk/genetics-control-homestasis/population-genetics-and-epigenetics/) - The sum of all present alleles for a given gene in a given population is known as the gene pool. In the wild, each species may exist as one population or multiple populations. This is essentially a way of thinking about all the individuals in a population contributing their alleles towards the overall allele frequency.
- [Patterns of inheritance](https://thealevelbiologist.co.uk/genetics-control-homestasis/patterns-of-inheritance/) - Its expression, however (that is what protein a gene encodes, and what that protein ends up doing in the organism) is a separate entity which is subject to environmental influence. This is called the phenotype. Humans have 2 sets of chromosomes, so for each distinct chromosome e.g. chromosome 1, there are two copies. How do the same genes on both homologous chromosomes interact if they result in different…
- [⚠️ Ethical considerations in the use of microorganisms — hazards and control of risks](https://thealevelbiologist.co.uk/metabolism-survival/ethical-considerations-in-the-use-of-microorganisms-hazards-and-control-of-risks/) - The use of microorganisms has a multi-fold hazard perspective. Some microorganisms are inherently pathogenic and very dangerous to humans e.g. anthrax by Bacillus anthracis. Others, and arguably most others, are not expected to have any negative effect on humans. However, given that some species turn pathogenic in some situations, it is a good idea to treat these other species as potentially pathogenic.
- [Genetic control of metabolism](https://thealevelbiologist.co.uk/metabolism-survival/genetic-control-of-metabolism/) - Genetic change can be brought about by using wild type organisms with their default DNA and inducing mutation e.g. through physiochemical routes like exposure to UV radiation or mutagenic chemicals; selective breeding to bring out recessive characteristics or emphasise particular traits; and culture of recombinant DNA that introduces artificial elements to the existing DNA, e.g. new sequences taken from a different species, an inhibitory sequence that switches off an existing function, etc.
- [Environmental control of metabolism](https://thealevelbiologist.co.uk/metabolism-survival/environmental-control-of-metabolism/) - Growing microorganisms has been a fundamental element of much of experimental biology, as well as the underpinning of many modern molecular biology techniques. Perhaps we have a sample of earth that we want to analyse to find a new microorganism with antibacterial properties. Perhaps we are testing a patient sample for an infectious agent. Most likely, we are culturing a safe strain of E. coli that has been genetically modified to produce a protein of interest like human insulin that we can isolate from it and administer to patients.
- [Metabolism and adverse conditions](https://thealevelbiologist.co.uk/metabolism-survival/metabolism-and-adverse-conditions/) - Maintaining an active metabolic rate may not be possible at all times. Adverse conditions mean that energy would be wasted on surviving in situations that don’t allow for reasonable living activities for a period of time. Therefore, metabolic rate must decrease to allow for this.
- [Metabolism in conformers and regulators](https://thealevelbiologist.co.uk/metabolism-survival/metabolism-in-conformers-and-regulators/) - Conformers such as the largemouth bass do not invest as much energy into maintaining their metabolic environment (homeostasis), overarchingly governed by temperature regulation i.e. thermoregulation. They save this energy, but the downside is that their environmental niche is quite narrow. If they are to follow the right environment to maintain their metabolism, it’s likely they can’t go far and wide.
- [Metabolic rate](https://thealevelbiologist.co.uk/metabolism-survival/metabolic-rate/) - The sum of all metabolic reactions in the body can be measured as a function of oxygen consumption, carbon dioxide production and heat production. Oxygen is needed in aerobic respiration, carbon dioxide is a byproduct of respiration, while heat is lost energy by many reactions. The higher these variables, the higher the metabolic rate is. Due to the big range of metabolic rates between organisms at rest versus active, for comparison purposes the resting metabolic rate is obtained.
- [Cell respiration](https://thealevelbiologist.co.uk/metabolism-survival/cell-respiration/) - Respiration is the cellular energy-yielding process that occurs across the life domains (bacteria, archaea, eykaryota). Its overall reaction is: glucose + oxygen –> carbon dioxide + water + heat energy. You can notice that it is essentially the reverse of photosynthesis. Don’t make the mistake of associating plants with photosynthesis, and non-plants with respiration.
- [Metabolic pathways and their control](https://thealevelbiologist.co.uk/metabolism-survival/metabolic-pathways-and-their-control/) - Metabolic pathways are the routes from chemical to chemical that represent their various reactions inside cells, catalysed by enzymes. Enzymes are proteins that enable a much faster reaction – catalysts. These pathways cover the making and breaking of all compounds. They cover the energy-producing processes that use oxygen and glucose to make ATP (adenosine triphosphate, the cellular energy currency), the breaking down of sugars, fats and proteins from food, the building of new enzymes, the constant breaking down of waste products and creation of maintenance molecules for energy and the many functions in the body, etc.
- [Sexual reproduction in plants](https://thealevelbiologist.co.uk/sexual-reproduction-in-plants/) - In terms of the formation of pollen grains and embryo sacs, the sequence of meiosis and mitosis between precursor stages of development is similar to that in mammals. Instead of mammalian testes and ovaries, plants have equivalent structures called anthers and ovules. You might notice the ovule is inside a structure also called ovary. The flower ovary is what later develops into fruit. You know, apples, pears, etc. Their seeds are what is created as a result of the processes about to be outlined, inside the ovule. Another point to note is that both reproductive structures, anthers and ovules are present in the same flower. There are species that only have one or the other, but it’s common for them to have…
- [Sexual reproduction in mammals](https://thealevelbiologist.co.uk/edexcel-as-cells-viruses-reproduction/sexual-reproduction-in-mammals/) - Gametes are these cells that are haploid are are used as part of sexual reproduction in mammals to enable more genetically diverse offspring, compared with asexual reproduction. Gametes are egg and sperm cells. Their development through meiosis involves multiple stages, dispersed throughout an individual’s lifetime as we will see for eggs which finish the first part of development even prior to the birth of the individual who may use them later.
- [Viruses](https://thealevelbiologist.co.uk/viruses/)
- [⚙️ Eukaryotic and prokaryotic cell structure and function](https://thealevelbiologist.co.uk/eukaryotic-and-prokaryotic-cell-structure-and-function/) - “The cell is the structural and functional unit of living things” I wrote. I wasn’t far off was I? So yes, the cell is the unit of life. It’s a delimited volume where the chemistry of life can happen. In unicellular organisms, the cell is themselves, the body, the whole, the organism.
- [Transport systems in plants](https://thealevelbiologist.co.uk/cells-chemicals-transport-gas/transport-systems-in-plants/) - Mass transport is required in multicellular plants due to their increased size, the variation in their metabolism as they photosynthesise and respire at different rates throughout the day or in different seasons, and the decreased surface area to volume ratio coming from their larger size.
- [Gas exchange in mammals and plants](https://thealevelbiologist.co.uk/cells-chemicals-transport-gas/gas-exchange-in-mammals-and-plants/) - In complex, multicellular organisms cells organise themselves in such a way that enables a greater structure and function. Cells differentiate into specific structures and functions, and organise themselves as such into tissues. The different tissues can then form organs with yet a higher level of structure and function, and organs can work together in certain broad areas of the organism’s structure and function by taking part in organ systems.
- [<strong>Transport systems in mammals</strong>](https://thealevelbiologist.co.uk/cells-chemicals-transport-gas/transport-systems-in-mammals/) - Key point: the oxygen-rich blood vessels entering an organ are called arteries, while the oxygen-depleted blood vessels leaving an organ are called veins. So a blood vessel entering the liver or kidneys would be an artery. A blood vessel leaving the liver or kidneys would be a…
- [The heart and monitoring heart function](https://thealevelbiologist.co.uk/the-heart-and-monitoring-heart-function/) - The key thing is that this circulation of a large amount of substances via a system of transportation is called mass flow, hence mass transport. But how does the oxygen acquired by the lungs actually reach every single cell of the body? A network of sorts is needed to do that. Many bigger and smaller tubes would come in handy. They would form like a… circulatory system.
- [Nucleic Acids](https://thealevelbiologist.co.uk/cells-chemicals-transport-gas/nucleic-acids/) - Nucleic acids are polymers of the nucleotide monomer and include the central biological molecules DNA (deoxyribonucleic acid), RNA (ribonucleic acid) and ATP (adenosine triphosphate), playing roles in inheritance, protein synthesis and metabolism. ATP is adenosine triphosphate, a nucleotide involved in metabolism and many biological processes (the molecular energy currency).
- [Proteins and Enzymes](https://thealevelbiologist.co.uk/proteins-and-enzymes/) - For example, if the R group was a hydrogen, the amino acid would be glycine. The next diagram shows condensation, and the subsequent formation of a bond between two amino acids (any two). This bond is a peptide bond. The resulting molecule is called a polypeptide.
- [Water and its importance in plants and animals](https://thealevelbiologist.co.uk/cells-chemicals-transport-gas/water-and-its-importance-in-plants-and-animals/) - So, water is polar. Because the oxygen in water has a negative charge relative to the hydrogens which bear a relative positive charge, ions such as those found in sodium chloride (NaCl) can bind respectively to the oxygen side or to the hydrogen side. Many of life’s basic reactions like condensation and hydrolysis rely on water being present.
- [Cells and microscopy](https://thealevelbiologist.co.uk/cells-chemicals-transport-gas/cells-and-microscopy/) - One of the unifying concept in biology, that is the cell, has been arrived upon in big part thanks to microscopy. Additionally, microscopes have enabled the accumulation of knowledge about the cellular components i.e. organelles. Microscopes use visible light, as well as electrons and lasers to produce images of very small specimens prepared on slides, often dissected in a specific manner and stained with dyes, some fluorescent.
- [Cell recognition and the immune system](https://thealevelbiologist.co.uk/cells-2/cell-recognition-and-the-immune-system/) - Immunity against invading pathogens is a crucial part of maintaining health. The body has adaptations which prevent invasion by pathogens, as well as processes in place to deal with those that manage to penetrate the body’s primary defenses. The skin and mucous membranes (e.g. mouth) are examples of such defenses. Sweat contains lysozyme which is an enzyme that breaks down…
- [Transport across cell membranes](https://thealevelbiologist.co.uk/cells-2/transport-across-cell-membranes/) - Phospholipids have a hydrophilic (water loving) head , and hydrophobic (water repelling) tails . This results in the formation of a phospholipid bilayer (double layer), which forms the basis for the plasma membrane. Fluid = the arrangement of proteins contained in the membrane is always changing. Mosaic = the proteins present are spread around in a…
- [All cells arise from other cells](https://thealevelbiologist.co.uk/cells-2/all-cells-arise-from-other-cells/) - The cell cycle refers to the distinct stages through which a cell goes, from the moment it becomes a cell to the moment it divides to result in 2 separate cells. Bear in mind that some cells cease to divide any longer after a certain period of time, depending on cell type. If that’s the case, they are said to be in resting phase termed G0 .
- [Methods of studying cells](https://thealevelbiologist.co.uk/cells-2/methods-of-studying-cells/) - You will need to know about the difference between light , transmission electron and scanning electron microscopes – LM, TEM and SEM. Both the latter (as the name suggests) use a beam of electrons, rather than light, to produce an image of the sample. TEM uses electrons which pass through the sample, so the resulting micrograph (image) shows everything within the sample in black and white , for example organelles in a cell. SEM uses electrons which scan the sample in 3D , resulting in a coloured micrograph with 3D detail, but no components from within the sample.
- [Structure of Prokaryotic Cells and of Viruses](https://thealevelbiologist.co.uk/cells-2/structure-of-prokaryotic-cells-and-of-viruses/) - Prokaryotes do not have a nucleus like eukaryotes do. Their DNA is not membrane-bound, just free in the cytoplasm. The extra features of prokaryotic cells vs. eukaryotic cells you must learn are: -the cytoplasm overall does not contain membrane-bound organelles such as mitochondria and endoplasmic reticulum
- [Structure of eukaryotic cells](https://thealevelbiologist.co.uk/cells-2/structure-of-eukaryotic-cells/) - The core components of cells are the outer membrane , the cytoplasm (substance inside which contains all other stuff) and the nucleus (contains DNA). All the other stuff is made up of various components with specific functions – these are called organelles .
- [Kidney Function](https://thealevelbiologist.co.uk/homeostasis/kidney-function/) - Here’s a fancy topic of the newer spec… I’ve never done the kidney so I spent my post-A levels life in total kidney ignorance and utter lack of knowledge of my urination habits and their complexity, oh what a fool I have been. You on the other hand are going to have the damn honour of actually having a clue about how the brain and the kidneys freshen our blood up all the time. Oh ye enlightened children, rise.
- [Negative Feedback](https://thealevelbiologist.co.uk/homeostasis/negative-feedback/) - We’ve all heard of diabetes – if it goes too high our organs sustain damage, if it goes too low a coma may be induced or even death. Welcome to homeostasis – the maintenance of physiological parameters within optimal range. The operation of an oven is an easy example of negative feedback acting both ways, which is how it usually acts.
- [DNA Replication (CCEA)](https://thealevelbiologist.co.uk/molecules/dna-replication/) - The DNA must stay intact and be copied with a high degree of accuracy in order for the two newly formed bacteria to develop and function as their parent – adequately. In multi-cellular organisms such as ourselves, DNA replication occurs as a prelude to cell division. For such a complex molecule, past scientists have had a challenging time working out the precise mechanism by which DNA replicates. Three hypotheses were made: (for this purpose imagine one DNA molecule)
- [DNA](https://thealevelbiologist.co.uk/molecules/dna/) - DNA (deoxyribonucleic acid) is a large molecule which carries the genetic information, or blueprint, of all life on Earth. Mutations arising in the DNA code account for the diversity upon which evolution by natural selection can work. Therefore, it is not far-fetched to say that DNA is one of the central, most important molecules in living organisms.
- [Lipids (CCEA)](https://thealevelbiologist.co.uk/molecules/lipids/) - Unlike proteins and carbohydrates, lipids are not polymers. Lipids which store energy are triglycerides, while those which form membranes are phospholipids. Triglycerides are formed by a molecule of glycerol with three fatty acids attached. The reaction which results in triglycerides is condensation. Their insolubility to water also comes in handy for waterproofing purposes such as the top side of plant leaves. In animals, fat can serve as insulation to conserve heat.
- [Haemoglobin (WJEC)](https://thealevelbiologist.co.uk/haemoglobin/) - Blood is fun! Blood is to body as the Thames is to London, although I sure hope slightly cleaner… Blood is roughly split into the plasma and blood cells including erythrocytes and leucocytes (neutrophils, eosinophils, monocytes, lymphocytes). Plasma is the solution that blood cells are found in, and as such acts as their extracellular matrix. For skin cells for example, the extracellular matrix is formed of collagen, so it’s different to have it essentially a liquid like plasma. Plasma is a water solution containing proteins, sugars, clotting factors (as well as platelets involved in clotting), hormones, electrolytes, carbon dioxide and oxygen.
- [Inorganic Ions (CCEA)](https://thealevelbiologist.co.uk/molecules/inorganic-ions/) - Inorganic ions like nitrate (NO3–), calcium (Ca2+), hydrogen carbonate (HCO–3), potassium (K+), iron (Fe), magnesium (Mg2+) and phosphate (PO43-) are key components of molecules in living things. Here are a few examples of where they can be found and what their role is within plants.
- [Water (CCEA)](https://thealevelbiologist.co.uk/molecules/water/) - Take for example alphabet soup. In the beginning, it’s just a dry a$$ powder, overly salty, overly hard, overly dry, totally inedible and all-round disappointing. But add a bit of hot water and BAM! you have yourself a totally delicious, mind-blowingly satisfying dish. Same with life. It can’t just be earth. It needs water.
- [Aerobic respiration and photosynthesis: ATP production](https://thealevelbiologist.co.uk/importance-of-atp/aerobic-respiration/) - Cellular respiration produces ATP (adenosine triphosphate), the energy currency in biochemical processes. Oxygen-aided respiration – aerobic respiration – produces much more ATP than anaerobic respiration. The details of these processes are covered in later topics.
- [Protein Structure](https://thealevelbiologist.co.uk/chemical-elements-joined/protein-structure/) - Proteins are at the heart of living organisms. Their functions are very varied, from the hair on your head, to the haemoglobin in your red blood cells (which carries oxygen around the body), to the claws of a lion, to insulin (blood glucose regulation). All these highly varied proteins are made of their building blocks – amino acids. This is what the generalised structure of an amino acid looks like (make sure you can draw this):
- [Lipids (WJEC)](https://thealevelbiologist.co.uk/chemical-elements-joined/lipids/) - Cell membranes are made of phospholipids, which are made of lipids. Lipids are the stuff of oils, fats and waxes. They’re not water soluble which makes them good for energy storage as their presence doesn’t interfere with the amount of solutes in the cell’s water (water potential) and their structure holds a lot of chemical energy (hence why fats have more than double the amount of calories when consumed compared to either carbohydrates or proteins). Their insolubility to water also comes in handy for waterproofing purposes such as the top side of plant leaves. In animals, fat can serve as insulation to conserve heat.
- [Starch, Cellulose and Chitin](https://thealevelbiologist.co.uk/chemical-elements-joined/starch-glycogen-cellulose-chitin/) - Alpha glucose is what’s termed in chemistry a cis isomer while beta glucose is a trans isomer. Cis because the hydrogen (top, H) and hydroxyl (bottom OH) groups on the left and right of the glucose are on the same side of each other, and for beta glucose it’s trans because they are across from each other diagonally, and not on the same side.
- [Carbohydrate structure and function (WJEC)](https://thealevelbiologist.co.uk/chemical-elements-joined/carbohydrate-structure-and-function/) - The smallest units (monomers) of carbohydrates are simple sugars and include trioses, pentoses and hexoses, so named due to the number of carbon atoms present (3, 5 and 6 respectively). They are monosaccharides. The triose glyceraldehyde for example, is an intermediate in the metabolism of carbohydrates to produce energy during cellular respiration. The pentose deoxyribose is a constituent of no other than DNA itself, while the hexose glucose needs no introduction as the central energy processing molecule created in photosynthesis and expended in respiration.
- [Water (WJEC)](https://thealevelbiologist.co.uk/chemical-elements-joined/water/) - But add a bit of hot water and BAM! you have yourself a totally delicious, mind-blowingly satisfying dish. Same with life. It can’t just be earth. It needs water. It needs a solvent, a containment environment for its chemicals. Many of life’s basic reactions like condensation and hydrolysis rely on water being present.
- [Inorganic Ions (WJEC)](https://thealevelbiologist.co.uk/chemical-elements-joined/inorganic-ions/) - Inorganic ions like iron (Fe2+), calcium (Ca2+), magnesium (Mg2+) and phosphate (PO43-) are key components of molecules in living things. Here are a few examples of where they can be found and what their role is within plants. Calcium ions have a key role in calcium pectate which I have just googled. I’m afraid what I found is far too hilarious to ignore: “Calcium pectate, a pectin fiber that adds crispness to fruits and vegetables, also has potent cholesterol-lowering properties.”
- [Human Populations](https://thealevelbiologist.co.uk/legacy-topics/human-populations/) - The Demographic Transition Model is a model used to classify different populations depending on their birth rate, death rate, overall population size, and the factors behind these numbers. There are 5 different…
- [Variation in Population Size](https://thealevelbiologist.co.uk/variation-in-population-size/) - Non-living factors such as light intensity, temperature and humidity determine the number of organisms that a habitat can sustain. All species have a varying degree of ability to withstand harsh or fluctuating conditions, called resilience. If an abiotic factor changes dramatically in favour of a population – for example, plenty more light in a field – then the population will increase provided no other factors are limiting. The opposite is true if an abiotic factor changes against the resilience limit of a population – it will decrease.
- [Investigating Populations](https://thealevelbiologist.co.uk/investigating-populations/) - Where do you even begin to count the number of organisms in a field, for example? How can quantitative data be obtained for a rocky shore? It’s not feasible to assess every single individual plant, count all the crabs you can possibly find, or estimate the abundance of all types of grass along a shingle ridge. Even if that was possible, the data would still not apply to the make up of a population, for example, at different times.
- [Populations and Ecosystems](https://thealevelbiologist.co.uk/populations-and-ecosystems/) - What is a population? A population is all the individual organisms found in a given habitat, of one species. So you could talk about a population of wolves in the woods. If you want to talk about the wolves and rabbits in the woods, then you’d be referring to a community. A community is made up of the various populations in a habitat. So the summation of all the living things in a given area is called a community. What then is an ecosystem?
- [Index of Diversity](https://thealevelbiologist.co.uk/index-of-diversity/) - Species diversity is described as the number of species in a community. The more species, the higher the diversity. What if there are two separate communities like this: Community #1 has 150 individuals per each of 20 different species (3000 individuals in total). Community #2 has 10 individuals per each of 19 species, and 2990 individuals of the last species (3000 individuals in total)
- [Species Diversity](https://thealevelbiologist.co.uk/legacy-topics/species-diversity/) - It’s not hard to figure out the impact both have on species diversity. Deforestation practically removes many, whole trees, and with them goes the shelter and food source of many other organisms. A great reduction in species diversity can be…
- [Genetic Variation in Bacteria](https://thealevelbiologist.co.uk/genetic-variation-in-bacteria/) - As generations of bacteria come to life, their DNA doesn’t stay completely identical. Random mutations sometimes arise. Mutations are changes in DNA which result in different characteristics. No, not bacteria with fangs, but subtle changes in, say, the shape of…
- [The Sliding Filament Theory of Muscle Contraction](https://thealevelbiologist.co.uk/the-sliding-filament-theory-of-muscle-contraction/) - How do muscles contract? Glad you should ask. Look in any book and you’ll probably be scarred and put off completely. I know I was! I mean what is the deal with Z line, A band, I band…?! So let’s look into it very gently indeed. First off, a good idea about what muscles look like on a bigger scale:
- [☀️ Survival and Response](https://thealevelbiologist.co.uk/legacy-topics/survival-and-response/) - One particularly obvious category of response to the environment in organisms is movement. This is one of the most fundamental ways for a plant or an animal to enhance survival. It’s no wonder then, that much of this response is solidly built-in and automated, like a reflex. There are 3 main examples of response: tropism, taxis and kinesis and reflex.
- [<strong>The Biological Basis of Lung Disease</strong>](https://thealevelbiologist.co.uk/the-biological-basis-of-lung-disease/) - Tuberculosis (TB) is an infectious disease of the lungs which causes constant coughing with blood, shortness of breath, fever and weight loss over the years. Every year 2 million people die from TB out of 8/10 million who get the disease. Far more people, around 2 billion, carry the TB bacteria on them without having the disease.
- [Lung Function](https://thealevelbiologist.co.uk/lung-function/) - The human gas exchange system is made of the trachea, from which the bronchi branch off, followed by the bronchioles into the lungs, and finally the alveoli, which are the functional unit of the lungs. Of course this is nonsense without an image:
- [Cholera](https://thealevelbiologist.co.uk/cholera/) - As all bacteria, Vibrio cholarae is a prokaryotic organism. Prokaryotes do not have a nucleus like eukaryotes do. Their DNA is not membrane-bound, just free in the cytoplasm. The features of prokaryotic cells you must learn are…
- [Absorption](https://thealevelbiologist.co.uk/absorption/) - When carbohydrates from food are digested, lots of glucose molecules, along with some fructose and galactose, are produced in the small intestine. Initially the mode of transport of glucose in absorption is diffusion. It is then followed by facilitated diffusion via co-transport, where glucose molecules are absorbed along with a sodium ion (Na+) through a carrier protein. This method is much faster than diffusion by itself.
- [Active Transport](https://thealevelbiologist.co.uk/active-transport/) - Unlike diffusion, osmosis and facilitated diffusion, active transport requires energy in the form of ATP (adenosine triphosphate), and moves substances against a concentration gradient (from a lower concentration to a higher concentration). This process is essential in removing of all toxins from the body, as well as the movement of rare chemicals.
- [Osmosis](https://thealevelbiologist.co.uk/osmosis/)
- [Passive Transport](https://thealevelbiologist.co.uk/cell-membranes-transport/diffusion/) - Diffusion takes place when you use a spray in a room, for example. The particles in the spray move randomly, knocking each other, which results in them spreading throughout the room gradually, from high concentration to low concentration. Therefore, diffusion acts down (or along) a concentration gradient.
- [Plasma Membranes](https://thealevelbiologist.co.uk/plasma-membranes/) - Membranes are made of phospholipids, which are made of lipids. Lipids are the stuff of oils, fats and waxes. Unlike proteins and carbohydrates, lipids are not polymers. Lipids which store energy are triglycerides, while those which form membranes are phospholipids. Triglycerides are formed by a molecule of glycerol with three fatty acids attached. The reaction which results in triglycerides is condensation.
- [Cells](https://thealevelbiologist.co.uk/cells/)
- [Carbohydrate Digestion](https://thealevelbiologist.co.uk/carbohydrate-digestion/) - α (alpha) glucose is the most important monosaccharide to learn, as you need to be able to draw it. The points where the lines intersect each symbolise a carbon (C) atom. So the monosaccharide alpha glucose (commonly, just glucose) somehow becomes a polysaccharide. This is achieved by condensation reactions, and the bonds formed are called…
- [Enzyme Action](https://thealevelbiologist.co.uk/enzyme-action/) - Enzymes are proteins which catalyse (speed up) metabolic reactions. Like all other catalysts (e.g. in chemistry), enzymes achieve this by lowering the activation energy (energy needed for a reaction to occur) of a reaction, by forming an enzyme-substrate complex.
- [The Digestive System](https://thealevelbiologist.co.uk/the-digestive-system/) - You only need to learn these bits: oesophagus, stomach, small intestine, large intestine, rectum; as well as the glands associated with the digestive system: the salivary glands and the pancreas.
- [Lifestyle](https://thealevelbiologist.co.uk/lifestyle/) - Apart from specific, easily identifiable pathogens such as bacteria or viruses which can cause disease, another major cause of disease is lifestyle. Lifestyle includes the choices that we make in regards to our food, drink, whether we smoke or use drugs, certain jobs we do, even the place where we live.
- [Pathogens](https://thealevelbiologist.co.uk/pathogens/) - Pathogens are microorganisms which can cause disease. These include bacteria, viruses and fungi. Have a look at the little things! (Did you know viruses aren’t actually “alive”? They’re more like seeds – they multiply under certain conditions, but otherwise, they’re dead.) Pathogens can cause disease when they invade the interface between an organism and their environment. This could be someone’s skin, lungs, digestive system, etc.
- [Nutrient cycles (AQA)](https://thealevelbiologist.co.uk/nutrient-cycles/) - At the heart of both the phosphorus and nitrogen cycles are microorganisms such as bacteria. These key nutrients pass from plants to animals through ingestion and digestion (eating!) in a very straightforward way, but what happens after those organisms die is a far more interesting tale.
- [Energy and Ecosystems](https://thealevelbiologist.co.uk/energy-and-ecosystems/) - But wait. Don’t plants also use their own photosynthesised goodies (glucose) to provide energy for their own business (growth, reproduction, etc.) via respiration, and waste stored energy in their tissues upon their death? Of course they do. So less must be available for whatever eats the plant. And whatever eats the plant will also lose energy through…
- [⛅ Photosynthesis (Edexcel)](https://thealevelbiologist.co.uk/photosynthesis/) - Photosynthesis is a metabolic process which makes stuff using light. How? How can you make anything from light? And why? Living things are made of complex organic molecules such as carbohydrates and proteins, as opposed to simple inorganic molecules such as carbon dioxide and water.
- [Photosynthetic pigments](https://thealevelbiologist.co.uk/photosynthetic-pigments/) - The energy stored in big molecules (such as carbohydrates) created via photosynthesis is derived in part through the light energy in photons. In order to tap into this energy, light must be absorbed by plants and other photosynthetic organisms.
- [Anaerobic Respiration](https://thealevelbiologist.co.uk/anaerobic-respiration/)
- [Oxidative Phosphorylation](https://thealevelbiologist.co.uk/oxidative-phosphorylation/) - The NADH harvested from the Krebs cycle is oxidised back to NAD. This produces a stream of free electrons because, remember, oxidation = loss of protons or electrons. These electrons progress through the electron transport chain from coenzyme to coenzyme, down an energy gradient. Eventually they must be accepted by a terminal electron acceptor. This is oxygen, and that is why O2 is needed in aerobic respiration. The product is water, H2O.
- [Link reaction and Krebs cycle](https://thealevelbiologist.co.uk/energy-biological-processes/link-reaction-and-krebs-cycle/) - The pyruvate proceeds to being oxidised to a compound called acetyl coenzyme A upon reaction with coenzyme A which results in the production of yet another NADH and, voila! a carbon dioxide molecule, our first ever CO2; please welcome it graciously…
- [Glycolysis](https://thealevelbiologist.co.uk/glycolysis/) - Glycolysis literally means a glucose molecule is hydrolysed (broken down) by water into two. I bet you’re itching to find out what it’s broken down into. Glad you asked. It’s broken down into these molecules called pyruvate.
- [Aerobic Respiration](https://thealevelbiologist.co.uk/aerobic-respiration/) - You can notice that it is essentially the reverse of photosynthesis. Of course not all organisms obtain their respiration substrate (e.g. glucose/food) by making it themselves as plants do, yet all carry out respiration. Don’t make the mistake of associating plants with photosynthesis, and non-plants with respiration. They are different processes. Plants photosynthesise and respire at the same time, we eat plants and…
- [Plant reproduction](https://thealevelbiologist.co.uk/plant-reproduction/) - Flowering plants (angiosperms) reproduce sexually via cells produced in their flowers. The environmental conditions that stimulate flowering in plants include a period of cold i.e. chill time that informs the plant what time of the year it is. It would be a waste to flower in autumn because the approaching winter would bring conditions not favourable to survival and dispersal of seeds from the flower.
- [The impact of population increase](https://thealevelbiologist.co.uk/energy-reproduction-populations/the-impact-of-population-increase/) - Human populations grow and shrink due the balance between births and deaths. The number of births per 1000 people is called the birth rate, and the number of deaths per 1000 people is the death rate.
- [Photosynthesis, food production and management of the environment](https://thealevelbiologist.co.uk/photosynthesis-food-production-and-management-of-the-environment/) - The vast majority of plants on Earth today undergo photosynthesis via a specific route (C3) which is slightly different to two other potential routes (C4 and CAM). The general balanced reaction for photosynthesis is: H2O + CO2 + energy –> C6H12O6 + O2 …where water, carbon dioxide and energy are the starting materials, and glucose and oxygen the products. Here, glucose is the key product because it is the complex organic molecule made from simple inorganic reactants. The “energy”, as you may have noticed, is where the light comes in.
- [The effects of ageing on the reproductive system](https://thealevelbiologist.co.uk/the-effects-of-ageing-on-the-reproductive-system/)
- [Fertility and assisted reproduction](https://thealevelbiologist.co.uk/fertility-and-assisted-reproduction/) - Urinogenital (a.k.a. urogenital; genitourinary) systems play roles in excretion (releasing urine produced by the kidneys) and reproduction via the genitals. The grouping arises due to the physical proximity of the systems, their common developmental pathway, and some of their shared pathways.
- [Metabolism and exercise](https://thealevelbiologist.co.uk/metabolism-and-exercise/) - Exercise has short-term and long-term effects on the respiratory and cardiovascular systems, and on skeletal muscle. Short-term, heart rate as well as cardiac output, respiratory rate and tidal volume increase in order to provide more oxygenated blood to working muscles. These refer to how fast the heart beats, how much blood the heart pumps, how many breaths are taken and how much air is inhaled by the lungs.
- [Cellular Respiration](https://thealevelbiologist.co.uk/cellular-respiration/) - Respiration is the cellular energy-yielding process that occurs across the life domains (bacteria, archaea, eykaryota). Aerobic respiration, as opposed to anaerobic respiration, occurs in the presence of oxygen, accounts for most respiration that takes place, and produces up to 15 times more ATP molecules.
- [➗ Protein control of cell division](https://thealevelbiologist.co.uk/protein-control-of-cell-division/) - Cell division requires the active remodelling of the cell’s cytoskeleton. The cytoskeleton is made of multiple kinds of protein that offer it the right structure and aid during the process of division. The centriole is a tubey spaghetti thing that aids in cell division when the duplicated chromosomes need to move into their subsequent new offspring cells from the parent cell (during mitosis).
- [Communication within multicellular organisms](https://thealevelbiologist.co.uk/communication-within-multicellular-organisms/) - Communication therefore is the connection between these different receptors, whether they are present (if not, the signal simply won’t be read) or not, and the signal molecules. Moreso, signals themselves can cause a production or reduction of receptors in cells. The same signal molecules can also result in different outcomes in different tissues. Welcome to biology!
- [⚡ Detecting and amplifying an environmental stimulus](https://thealevelbiologist.co.uk/etecting-and-amplifying-an-environmental-stimulus/) - Photoreceptors are an example of receptors found across all three domains of life. In addition to the ubiquitous use in the animal kingdom of eyes, and light-using photosynthesis in plants, photoreceptors are also central to the driving force of proton gradients in archaea for their cellular functions.
- [Membrane proteins](https://thealevelbiologist.co.uk/membrane-proteins/) - Since membrane proteins are found at the interface between cells, unsurprisingly one of their key functions is transport of molecules and ions across the membrane, since many can’t make their way on their own. The main properties of molecules that determine how they may be transported across a membrane are solubility, size and charge.
- [Laboratory techniques for biologists](https://thealevelbiologist.co.uk/laboratory-techniques-for-biologists/) - Much biological research relies on the use of chemicals and organisms. Some of these are an inherent health and safety hazard. For example, most pure chemicals are irritants in certain doses, while others such as organic solvents and fungicides can be straight-up lethal to humans even in small doses.
- [Genomic sequencing](https://thealevelbiologist.co.uk/dna-genome/genomic-sequencing/) - Simple genomes such as those of viruses can enable a relatively straightforward effort of assigning proteins to each gene in the genome, and thus creating a database of them. This is known as a proteome. The information gleaned from a virus proteome, for example, can inform vaccination targets by selecting appropriate antigens such as elements of the viral capsid.
- [Evolution](https://thealevelbiologist.co.uk/dna-genome/evolution/) - Evolution refers to the changes over time experienced by living things, associated with genomic variation. The genetic material embodied by DNA transcends organisms in a few ways. One of them is vertical inheritance from parents to offspring via asexual or sexual reproduction. Another path is horizontal transmission between unrelated individuals, as seen between bacteria that exchange antibiotic resistance genes through the sharing of their plasmids.
- [Mutations](https://thealevelbiologist.co.uk/dna-genome/mutations/) - Mutations are a random occurrence during DNA replication and the rate of mutation is influenced by external factors such as UV radiation. Mutation occurs spontaneously. There are different types of mutation: 1. Deletion where one or more nucleotide bases are deleted. AGTCA becomes AGCA 2. Substitution where one or more nucleotide bases are replaced by others. AGTCA becomes AGTCG
- [The structure of the genome](https://thealevelbiologist.co.uk/dna-genome/the-structure-of-the-genome/) - As previously touched on, the genome is the entirety of genetic material carried by an individual or species and varies accordingly. The database of genomes of different species is growing and includes humans (the Human Genome Project). For example, the human genome, by chromosome, is viewable here: https://www.ncbi.nlm.nih.gov/genome/?term=homo+sapiens
- [Cellular differentiation](https://thealevelbiologist.co.uk/dna-genome/cellular-differentiation/) - Cells in our bodies have the same amount of DNA, and that DNA is completely identical! So how come a muscle cell and a brain cell both have very different structure and function despite that? How can cells be different to one another yet carry the same genetic information which codes for the same proteins? Indeed, how come most of a cell’s DNA is not translated?
- [Control of gene expression](https://thealevelbiologist.co.uk/dna-genome/control-of-gene-expression/) - While the genotype represents the genetic information contained by the totality of someone’s DNA, the phenotype represents the products from DNA and genes that actually get expressed (many genes are not expressed) to make an organism appear and function the way it does. These products are in the most obvious and tangible sense, proteins. Proteins are at the heart of biological organisation in both structure and function, and span a huge variety of types, from strong cartilage and protective keratin, to efficient digestive enzymes and oxygen-carrying haemoglobin.
- [Replication of DNA (Scottish Higher)](https://thealevelbiologist.co.uk/dna-genome/replication-of-dna/) - For such a complex molecule, past scientists have had a challenging time working out the precise mechanism by which DNA replicates. Three hypotheses were made: (for this purpose imagine one DNA molecule) 1. The DNA molecule replicates by providing itself as a template for a brand new shiny DNA molecule, and then remaining its own intact DNA molecule. This is called the conservative replication model.
- [The structure of DNA (Scottish Higher)](https://thealevelbiologist.co.uk/dna-genome/the-structure-of-dna/) - DNA (deoxyribonucleic acid) is a large molecule which carries the genetic information, or blueprint, of all life on Earth. Mutations arising in the DNA code account for the diversity upon which evolution by natural selection can work. Therefore, it is not far-fetched to say that DNA is one of the central, most important molecules in living organisms.
- [Practical skills assessed in the practical endorsement](https://thealevelbiologist.co.uk/practical-skills-are-assessed-in-the-practical-endorsement/) - This refers to you having the knowledge and confidence to approach a problem or experiment with common sense. It refers to you taking it upon yourself to understand the background, what is going on and what you might be able to do. Ask questions, find out information, update it as you go along. It’s not a test to trip you up, simply material with which you can toy.
- [Practical skills assessed in a written examination](https://thealevelbiologist.co.uk/practical-skills-assessed-in-a-written-examination/) - Variables are factors present in an experiment. Often, they are the factors that we are primarily interested in e.g. testing a food variable against an age variable. Due to the nature of experiments taking place in the actual world, many confounding variables can present themselves, more or less clearly, in experiments. Confounding variables are those variables which can overlap so that it cannot be obvious whether a result is due to one variable or another.
- [Water (Edexcel)](https://thealevelbiologist.co.uk/water/) - Water is to solvent as bear is to North Pole . It is polar. Water is a polar solvent. I could have just said it plainly but I had to insert a ludicrous arctic animal joke. So, water is polar. Because the oxygen in water has a negative charge relative to the hydrogens which bear a relative positive charge, ions such as those found in sodium chloride (NaCl) can bind respectively to the oxygen side or to the hydrogen side. Thus, the salt is soluble and…
- [ATP](https://thealevelbiologist.co.uk/atp/) - ATP is the energy currency of physiological processes. It stands for adenosine triphosphate, and it’s the product for which both aerobic and anaerobic respiration evolved! The removal of a phosphate group from ATP results in an adenosine diphosphate (ADP) molecule, the inorganic phosphate (Pi) and energy being released.
- [Replication of DNA](https://thealevelbiologist.co.uk/legacy-replication-of-dna/) - DNA, of course, replicates. Why? It’s a pretty crucial element in the reproduction of living things. For example, a bacterium replicates by splitting itself into 2 (binary fission). The DNA must stay intact and be copied with a high degree of accuracy in order for the two newly formed bacteria to develop and function as their parent – adequately. In multi-cellular organisms such as ourselves, DNA replication occurs as a prelude to cell division.
- [Structure of DNA and RNA](https://thealevelbiologist.co.uk/structure-of-dna-and-rna/) - DNA and RNA are key carriers of biological information. For example, DNA may store a gene coding for haemoglobin or insulin, which is then processed by RNA and ribosomes (which are sophisticated machines themselves made of RNA and proteins) to manufacture those proteins. Both DNA and RNA are nucleic acids (that’s the “NA” part of their acronym).
- [Many proteins are enzymes](https://thealevelbiologist.co.uk/many-proteins-are-enzymes/) - This can be described by the lock and key , and induced fit models of enzyme action. The lock and key model is based on complementary shapes between the enzyme and substrate. The substrate fits into the enzyme.
- [Proteins (Scottish Advanced Higher)](https://thealevelbiologist.co.uk/proteins/) - The complete set of genes in a cell is known as the genome while the full range of proteins a cell can make is the proteome. The proteome can be many times larger than its corresponding genome due to multiple arrangements of the mRNA product (alternative splicing) as well as post-translational modifications that can tweak the final protein in different ways based off the same polypeptide
- [Lipids (AQA)](https://thealevelbiologist.co.uk/lipids/) - The bonds formed (C-O) are called ester bonds . Fatty acids can be saturated or unsaturated (monounsaturated; polyunsaturated). Saturated fatty acids have all their carbon (C) atoms linked to hydrogen (H) atoms, hence saturated with hydrogen . If there is a carbon atom with a double bond to its neighbour carbon atom, then it will only have one bond to a hydrogen atom, hence it is unsaturated. If there is one double bond present, the fatty acid is monounsaturated . If there are multiple double bonds present, the fatty acid is polyunsaturated
- [Monomers and Polymers](https://thealevelbiologist.co.uk/monomers-and-polymers/) - Life in its ecosystems, species and organisms has been expressed, and continues to do so, in a great variety of ways. Yet on the biochemical level, deep down into the tissue, cells and microscopic components that make up these living things, the basic building blocks are the same! A bit like how everything is just made up of atoms or quarks or just empty space really but it somehow ends up looking really interesting to us.
- [Carbohydrates (CCEA)](https://thealevelbiologist.co.uk/molecules/carbohydrates/) - Glucose is a key carbohydrate in biology because it is the preferred fuel that provides energy during cellular respiration as well as the building block for complex polysaccharides and other compounds that use it such as glycoproteins. As a monomer, it is small and water soluble and thus accessible to cells for respiration. Plants and other organisms can create it through photosynthesis. It can be built into starch or glycogen and stored away for
- [Inorganic Ions (Edexcel)](https://thealevelbiologist.co.uk/inorganic-ions/) - Inorganic ions like nitrate (NO3–), calcium (Ca2+), magnesium (Mg2+) and phosphate (PO43-) are key components of molecules in living things. Here are a few examples of where they can be found and what their role is within plants. Nitrate ions are extracted by plants from the soil, and their nitrogen atoms used for other things. There are of course the nitrogenous bases in DNA (adenine, guanine, cytosine and thymine) as well as amino acids – hence amino acids. Get it get it.
- [DNA and Protein Synthesis (Edexcel)](https://thealevelbiologist.co.uk/dna-and-protein-synthesis/) - DNA (deoxyribonucleic acid) is a large molecule which carries the genetic information, or blueprint, of all life on Earth. Mutations arising in the DNA code account for the diversity upon which evolution by natural selection can work. Therefore, it is not far-fetched to say that DNA is one of the central, most important molecules in living organisms.
- [Proteins (Edexcel)](https://thealevelbiologist.co.uk/proteins-edexcel/) - Proteins are at the heart of living organisms. Their functions are very varied, from the hair on your head, to the haemoglobin in your red blood cells (which carries oxygen around the body), to the claws of a lion, to insulin (blood glucose regulation). All these highly varied proteins are made of their building blocks – amino acids. This is what the generalised structure of an amino acid looks like (make sure you can draw this):
- [Lipids (Edexcel)](https://thealevelbiologist.co.uk/lipids-edexcel/) - The bonds formed (C-O) are called ester bonds . Fatty acids can be saturated or unsaturated (monounsaturated; polyunsaturated). Saturated fatty acids have all their carbon (C) atoms linked to hydrogen (H) atoms, hence saturated with hydrogen . If there is a carbon atom with a double bond to its neighbour carbon atom, then it will only have one bond to a hydrogen atom, hence it is unsaturated. If there is one double bond present, the fatty acid is monounsaturated. If there are multiple double bonds present, the fatty acid is…
- [<strong><mark>Animal behaviour</mark></strong>](https://thealevelbiologist.co.uk/animal-behaviour/) - These actions are “hard-wired”, complex, stereotyped and species-specific. They are responses to a stimulus or trigger from the environment, but are more complex than simple reflexes. Stereotyped actions are rigid and have a strict structure that is followed each time.
- [<strong>Gram positive and gram negative bacteria</strong>](https://thealevelbiologist.co.uk/gram-positive-and-gram-negative-bacteria/) - Amongst bacteria, the cell wall composition is a key determinant of what type they belong to. This is important in terms of predicting their response to various antibiotics.
- [<strong>Biopharming</strong>](https://thealevelbiologist.co.uk/biopharming-2/) - Bio “farming” or biopharming for pharmaceuticals describes the practice of genetically engineering animals to produce foreign products of interest to humans.
- [<strong>Osteoporosis</strong>](https://thealevelbiologist.co.uk/osteoporosis/) - Osteoporosis is an aging-related condition where decreasing bone density puts patients at higher risk of fractures. Causes include increased bone resorption compared to bone formation, which overall reduces the bone density. This bone remodelling process is constant, and is susceptible to various factors including exercise and hormones.
- [<strong>RNA interference (RNAi)</strong>](https://thealevelbiologist.co.uk/rna-interference-rnai/) - A major component in the regulation of transcription and translation is RNA interference, notably via microRNA (miRNA) and small interfering RNA (siRNA).
- [<strong>Cytometry and bacterial growth</strong>](https://thealevelbiologist.co.uk/cytometry-and-bacterial-growth/) - Once the right environment is set up (often this means 37 deg. Celsius, shaking the flasks to introduce oxygen bubbles into the solution and optimise growth, leaving plates incubating overnight, etc.), growth can finally be monitored. There are many ways of doing this, such as cell count, viable cell count, mass and optical methods that detect turbidity.
- [<strong>Ethology</strong>](https://thealevelbiologist.co.uk/ethology/) - Ethology is the study of animal behaviour in their natural environment. An ethogram is a reference of all behaviours seen in a species in the wild.
- [<strong>Effects of tobacco smoking</strong>](https://thealevelbiologist.co.uk/effects-of-tobacco-smoking/) - The chemicals contained in tobacco cigarette smoke (several thousand types) do damage to the cilia that line the respiratory tract and move dirt particles away from the lungs e.g. pollutants, pathogens, dust. These protrusions from the lungs, trachea and nose are sensitive to toxins and following long periods of sustained damage can cease to function.
- [<strong>Antibody techniques</strong>](https://thealevelbiologist.co.uk/antibody-techniques/) - The high specificity of the antigen-antibody bond makes use of antibodies as a lab technique high on the list. Antibodies are used with proteins as a labelling method to detect presence of the target moiety (in biochemical reactions, testing or disease detection), or with whole tissue samples to detect presence of specific organelles for visualisation under a microscope.
- [<strong>Bioinformatics</strong>](https://thealevelbiologist.co.uk/bioinformatics/) - Bioinformatics is the field of studying the vast quantities of data generated in biology using appropriate technological tools. For example, there are hundreds of thousands, millions and tens of millions of pieces of data under different categories: published research papers, genes, protein information, documented variations and other information of different biological species, molecules and other categories.
- [<strong>Transgenic animals and plants</strong>](https://thealevelbiologist.co.uk/transgenic-animals-and-plants/) - Delivering DNA into cells for various purposes can be achieved via viruses which naturally can infect certain cells, as well as gene guns (biolistics) for plants. Delivering DNA to plants via gene guns involves firing tiny metal pellets covered with DNA into plant cells. Once inside the cell, the DNA delivered will be transcribed and translated by cell machinery. The protein encoded by the DNA depends on the gene included. This varies by…
- [<strong>Learned behaviour</strong>](https://thealevelbiologist.co.uk/option-b-neurobiology-behviour/learned-behaviour/) - If some behaviour is innate, other behaviour is learnt through various series of events that happen at critical times early in life, or later on and throughout. Habituation is a very primordial and simple learning mechanism that involves desensitisation to repetitive stimuli that are not rewarding nor harmful. Baby birds are habituated to the sound of falling leaves or birds of their own species, when they learn that they do not signal danger.
- [<strong>Reflex, taxis and kinesis</strong>](https://thealevelbiologist.co.uk/reflex-taxis-and-kinesis/) - There are behaviours which are innate and may not require any conscious thought. Escape reflexes, taxes (sg. taxis) and kineses (sg. kinesis) are types of innate behaviours that help organisms avoid danger, find food and respond to environmental stimuli quickly enough to be effective. Reflex – think of sensory neuron –> interneuron –> motor neuron
- [<strong>Gene expression and the brain</strong>](https://thealevelbiologist.co.uk/gene-expression-and-the-brain/) - Gene expression can be determined by methylation, histone modification and RNA regulators (see epigenetics) and is important as the stepping stone between the genome and proteome – what a gene codes for as opposed to what, and whether a protein is made as a result. The brain, its development, activity and health are all subject to the effects of gene expression. Many studies have revealed these connections. For example, specific epigenetic markers on the brain were found in victims of child abuse who committed suicide compared to suicide victims who had not experienced child abuse.
- [<strong>Brain development and neuroplasticity</strong>](https://thealevelbiologist.co.uk/brain-development-and-neuroplasticity/) - Brain development takes place significantly in the first part of life, and before birth. As a large and energy-hungry organ, its development starts from a simple location at the end of the nerve cord in the early embryo, to a highly complex structure with multiple areas, as neurons are synthesised in a stem cell rich part of the brain before migrating to their respective final locations. Neuron axons then start forging their way into tissue to their destination, sometimes very far from origin, by sensing their environment. Some of them can overgrow and later get “pruned”.
- [<strong>Brain study techniques</strong>](https://thealevelbiologist.co.uk/brain-study-techniques/) - There are multiple techniques available in research and medicine to study the brain for various purposes including diagnosis and psychology research. Functional magnetic resonance imaging (fMRI) is used moreso in research than medicine, and gives a picture of brain activity based on increased blood flow correlated with neural activity. This is based on the knowledge that wherever in the brain higher activity takes place, an increase in blood will take place. This creates a gradient between the deoxygenated haemoglobin in the blood and the oxygenated haemoglobin in the blood.
- [<strong>Language and speech</strong>](https://thealevelbiologist.co.uk/cerebrum-structure-and-function-involvement-in-language-and-speech/) - As seen previously, there are different parts of the cerebrum such as the motor cortex and the somatosensory cortex which are specialised in function. Alongside motor, sensory and specific cortex regions such as hearing and vision, there is also an area tasked with language comprehension and speech. This is called Broca’s area and it works alongside the auditory processing area and the motor cortex to accomplish one potential sequence of speech: hearing, processing and speaking.
- [](https://thealevelbiologist.co.uk/sensory-and-motor-areas-in-the-cortex/) - Different areas and sections in the cortex are associated with specific functions. Right on top and across the middle, there are two adjacent areas that have complementary functions: the motor cortex and the sensory cortex. They rest either side of the central sulcus which is the transversal dividing line. Neurones in the motor cortex extend axons down the length of the spine and establish connections via the spine to muscles to create voluntary muscle contraction and movement.
- [](https://thealevelbiologist.co.uk/hypothalamus/) - In the human brain the hypothalamus is an area the size of an almond located above the pituitary gland, and acts as a master-regulator in the endocrine system. The hypothalamus acts as a link between the nervous and endocrine systems by being connected neurally to the brainstem, amygdala and septum, and synthesising hormones together with the pituitary gland to regulate many body processes (homeostasis, hunger, circadian rhythm, reproduction, defence, etc.).
- [](https://thealevelbiologist.co.uk/sympathetic-and-parasympathetic-nervous-systems/) - Furthermore, the autonomous system is split into sympathetic and parasympathetic, the two acting antagonistically depending on the situation. They act on all body systems to spark alertness (fight or flight response) in the case of the sympathetic system, or the opposite (rest and digest) by the parasympathetic system. This acts on the pupils (dilation), the respiratory system, circulation, digestion, blood glucose, stress, excretion, etc.
- [](https://thealevelbiologist.co.uk/human-brain-structure-and-function/) - The brain has several key parts: the medulla oblongata, the cerebellum, the cerebrum, the hypothalamus and the hippocampus. The cerebrum is the uppermost part of the brain that contains many different lobes that control various voluntary functions such as speech, movement and…
- [](https://thealevelbiologist.co.uk/principles-homeostasis/) - Why, though, is it so important to keep a strict temperature and pH? From a physiological viewpoint, think of enzyme activity. Its sensitivity to both temperature and pH means that the only conditions of optimal function will be strictly defined. Lots of enzymes denature past 40°C and are inactivated below 35°C.
- [](https://thealevelbiologist.co.uk/principles-coordination/) - Effectors in the body such as muscles and glands may get their signals to contract or secrete substances in two ways: electrically by nerve impulses or chemically by hormones. Nerve cells have electrical impulses pass along them which results in their secretion of a neurotransmitter onto the target cells which respond quickly, locally and in a short-lived way.
- [](https://thealevelbiologist.co.uk/nitrogen/) - As briefly touched on in “Energy and Food Production”, the nitrogen contained in fertilisers used to enhance plant growth can deviate from the expected cycle when fertilisers end up in the wrong location. This is how fertilisers can reach further areas than planned, by the action of rain and irrigation.
- [](https://thealevelbiologist.co.uk/principles-of-immunology/) - Immunity against invading pathogens is a crucial part of maintaining health. The body has adaptations which prevent invasion by pathogens, as well as processes in place to deal with those that manage to penetrate the body’s primary defenses. The skin and mucous membranes (e.g. mouth) are examples of such defenses. Sweat contains lysozyme which is an enzyme that breaks down bacterial walls.
- [](https://thealevelbiologist.co.uk/genetic-diversity/) - The genetic diversity between organisms is accounted for by variation in DNA. Even a tiny difference in DNA can result in a lot of variation. What’s more, even identical DNA can still result in variation due to certain genes being active and others not. Is it visible that these two have largely identical DNA?
- [](https://thealevelbiologist.co.uk/dna-and-chromosomes/) - DNA and chromosomes may seem like completely separate things. Well, they’re not. In fact, all chromosomes are individual DNA molecules coiled and twisted around, because DNA is huge. At least in eukaryotes it is. That’s one of the first differences between eukaryotes and prokaryotes in their DNA – prokaryotes have less DNA.
- [](https://thealevelbiologist.co.uk/genes-and-polypeptides/) - DNA is deoxyribonucleic acid, a real molecule which can be viewed using an electron microscope, and which (were you very, very, very small) you could poke. A gene, on the other hand, is just a location, called a locus (locus means location, all hail Latin!) on a specific strand of DNA, which contains the encoded information used to make a certain polypeptide which has a specific role in the development and function of an organism. This code is determined by the sequence of bases (A, T, C and G) at that location.
- [](https://thealevelbiologist.co.uk/structure-of-dna/) - DNA is one of the central, most important molecules in living organisms. For such an important molecule, it sure looks beautiful …actually, in reality it looks more like this: Pink candy floss anyone? The above image is a scanning electron micrograph, as you can see the 3D shape of DNA. The pink colour is likely due to…
- [](https://thealevelbiologist.co.uk/courtship-behaviour/) - The first feature of courtship behaviour is that it enables organisms to identify members of their own species. The central part of the definition of a species is the members’ ability to produce viable offspring. Hence, attempting to mate with members of a different species is not an advantageous behavioural trait in the context of reproductive success.
- [](https://thealevelbiologist.co.uk/genetic-comparisons/) - More reliable and accurate than mere physical resemblance in determining the genetic relationship between individuals and species, is of course a genetic comparison. This can be achieved either by directly analysing their DNA, or the proteins encoded by it.
- [](https://thealevelbiologist.co.uk/legacy-topics/principles-of-taxonomy/) - Taxonomy refers to the classification of living things by giving unique names to each species, and creating a hierarchy based on evolutionary descent. This is a challenging task, as most species that have ever lived on this planet are now extinct, and many more alive today have yet to be discovered and classified.
- [](https://thealevelbiologist.co.uk/the-passage-of-water-through-a-plant/) - Roots, as you may have seen in real life, are hairy. All those tiny and not so tiny root hairs buried into the soil greatly increase the surface area of the root. This exposes it to more water molecules which can be taken up. The hairs are nothing like human hairs; they are extensions of the outer layer of the root, made up of cells. This layer is called the epidermis.
- [](https://thealevelbiologist.co.uk/the-blood-system/) - Cells in mammals require a constant supply of nutrients and oxygen, and a way to remove waste products. Blood is great, as it does all that. Blood needs a way of getting to all cells of the body, a way to… circulate. Without that, blood would just get pulled by gravity towards the centre of the earth. Not a pretty sight I’m afraid.
- [](https://thealevelbiologist.co.uk/cell-differentiation/) - All of the cells in your body, every single last cell, can be traced back to just a single cell (the fertilised egg a.k.a. zygote), and a single DNA code. How is it possible for hundreds of different cell types to arise from that? The zygote undergoes mitosis, and according to that, all daughter cells resulting are genetically identical. Therefore, all cells in our body must be genetically identical. Well, they are*. So how do all these supposed “clone cells” end up being so different from one another, and hence achieve such different purposes within the larger organism?
- [](https://thealevelbiologist.co.uk/gene-mutation/) - Since the genetic code is degenerate, it’s possible that a mutation won’t have any effect whatsoever! This represents silent mutations. If 2 different triplet codes translate into the same amino acid, the polypeptide chain will remain unchanged. This of course only applies to…
- [](https://thealevelbiologist.co.uk/legacy-topics/temperature-control/) - Not all organisms maintain their body’s core temperature the same way. Some control it internally like we do. We’re endothermic. Reptiles for example are not. They’re ectothermic. Two pennies for who guesses how these fine specimens maintain their temperature. Do they: A) Run for heat? B) Shiver for heat? C) Sit where the sun shines?
- [](https://thealevelbiologist.co.uk/muscles-as-effectors/) - Muscles use ATP from aerobic respiration to contract. However, depending on muscle type (below), anaerobic respiration may be carried out to provide energy very quickly. When this is the case, a reaction involving both ATP and PCr (phosphocreatine) occurs. The trick here is that unlike typical anaerobic respiration, no lactate is produced.
- [](https://thealevelbiologist.co.uk/energy-and-food-production/) - In the wild, both plants and animals are subject to a lot of energy loss due to pests, physical activity or insufficient nutrients. This results in a relatively inefficient flow of energy between trophic levels. We think of this in terms of net productivity. Net productivity is equal to gross productivity minus respiratory loss. In both terms, productivity refers to the amount of leftover useful tissue such as cereals or animal flesh.
- [](https://thealevelbiologist.co.uk/legacy-topics/investigating-variation/) - Chance plays an important role in sampling. Chance cannot be eliminated, but the probability of variation being due to chance can be decreased by collecting a large sample, and random sampling. In this case, the height of clovers would be considered continuous variation, as opposed to discontinuous. Continuous means that the clovers can have any height between certain values e.g. 2.1cm, 2.2cm or 2.25. Could one clover have a height of 2.24cm? Yes, that’s perfectly possible.
- [](https://thealevelbiologist.co.uk/the-biological-basis-of-heart-disease/) - As you can see, it leads to the narrowing of arteries, causing a lowering of blood supply. Atheroma is associated with an increased risk of aneurysm and thrombosis. Aneurysm is a ballooning of the artery which weakens the affected area. This requires urgent treatment, otherwise it is fatal if the balloon “pops”. Thrombosis is a blood clot stuck in a vessel which results in less blood supply to a specific area, and the subsequent affected tissues may be starved of blood and…
- [](https://thealevelbiologist.co.uk/heart-structure-and-function/) - There are two types of circulation going on via the heart: pulmonary circulation and systemic circulation. Pulmonary circulation is a short-distance route between the heart and the lungs, where deoxygenated blood is taken to be replenished with oxygen. Although normally veins take blood away, and arteries take blood to, in the case of pulmonary circulation things are the opposite way around.
- [Respiration](https://thealevelbiologist.co.uk/respiration/) - Don’t make the mistake of associating plants with photosynthesis, and non-plants with respiration. They are different processes. Plants photosynthesise and respire at the same time, we eat plants and respire at the same time. Similarly, don’t confuse respiration with ventilation. In the context of biology, ventilation is the movement of air through our respiratory system i.e. breathing, while respiration is the process by which…
- [Haemoglobin](https://thealevelbiologist.co.uk/haemoglobin-3/) - Haemoglobin is a type of protein. It is present in many varied organisms on our planet, and has a similar chemical structure in all of these organisms. In humans, haemoglobin is found in red blood cells. Haemoglobin’s function is the transport of oxygen around the body. Oxygen must reach all parts of our bodies because it is required in the process of cellular respiration (to produce ATP – the main molecule involved in releasing energy for all uses).
- [Speciation](https://thealevelbiologist.co.uk/speciation-2/) - What is at the heart of new species formation? It all starts with a single population of a species which for whatever reason (genetic bottlenecks, founder effect, etc.) ends up being split geographically to the point where no interbreeding occurs for a certain length of time.
- [Energy Transfer](https://thealevelbiologist.co.uk/energy-transfer-2/) - Where do we get all our energy from? Food. Where does the energy in food ultimately come from? Plants. Where does the energy in plants ultimately come from? Nowhere, they make it themselves through photosynthesis. So is all the energy available to all living things on Earth down to photosynthesis? It sure is, my biologist friend, it sure is. Let’s take a humbling moment of meditation while adoring this photo of a plant:
- [Limiting Factors](https://thealevelbiologist.co.uk/limiting-factors-2/) - Photosynthesis, just like all other physiological processes in living things as well as chemicals and beyond, is subject to external influences. The main factors that weigh in on the efficiency and speed of photosynthesis are temperature, CO2 concentration and light intensity.
- [Selection](https://thealevelbiologist.co.uk/selection/) - The allele frequency in a population’s gene pool can change as a result of selection. The effectors of selection can be varied, yet the outcome is similar: advantageous or preferred alleles and the traits associated with them increase in frequency, while detrimental or disfavoured alleles and the traits associated with them decrease in frequency.
- [Succession](https://thealevelbiologist.co.uk/succession-3/) - Succession is the process by which this: …turns to that: It may be classified as primary succession or secondary succession. The difference is that the above is primary i.e. it begins with totally barren land devoid of any nutrients or other abiotic factors (water, wind, temperature) conductive to life thriving, while secondary succession occurs after an already-thriving community has been wiped out by natural disasters such as a wild fire.
- [Photosynthesis](https://thealevelbiologist.co.uk/photosynthesis-3/) - The vast majority of plants on Earth today undergo photosynthesis via a specific route (C3) which is slightly different to two other potential routes (C4 and CAM). The general balanced reaction for photosynthesis is
- [Inheritance](https://thealevelbiologist.co.uk/inheritance-2/) - Back in the day, Mendel crossed different varieties of pea plants to establish rules of inheritance. He didn’t know what we know today about genes and DNA. So what do we know, and what did he find out? The entirety of genetic material in an organism is called a genotype. It can also refer to specific things, like a genotype for a certain trait in a given organism.
- [Inorganic Ions (AQA)](https://thealevelbiologist.co.uk/inorganic-ions-2/) - Inorganic ions are EVERYWHERE. ALL OF THEM EVERYWHERE. They’re up in your cytoplasm and all up in your tissue fluid and some of them are like super high in concentration like sodium and potassium while others are like uber low otherwise u dead. We talkin about hydrogen ions that determine pH which is the acidity or alkalinity of e.g. your blood. This is key to basically all the proteins circulating and all the cell reactions and everything.
- [Water (AQA)](https://thealevelbiologist.co.uk/water-2/) - I mean, water. What more is there to say? It’s water for crying out loud. It does cool tricks. Take for example alphabet soup. In the beginning, it’s just a dry a$$ powder, overly salty, overly hard, overly dry, totally inedible and all-round disappointing. But add a bit of hot water and BAM! you have yourself a totally delicious, mind-blowingly satisfying dish.
- [Haemoglobin (CCEA)](https://thealevelbiologist.co.uk/haemoglobin-2/) - arbon dioxide and oxygen are transported in the blood under different conditions. Carbon dioxide is more soluble than oxygen, so some of it is directly present in the blood plasma. It can also be present as bicarbonate ions which increase blood acidity and signal if there is too much CO2 in the blood and not enough O2. Finally, both CO2 and O2 can bind to haemoglobin which is present in red blood cells. Its function is the oxygenation of tissues, as oxygen is central to aerobic respiration, the metabolic process of creating chemical energy for all cell functions.
- [Diffusion](https://thealevelbiologist.co.uk/diffusion-2/) - Diffusion = the spread of particles from a region of higher concentration to a region of lower concentration, until the particles are evenly spread out. Diffusion takes place when you use a spray in a room, for example. The particles in the spray move randomly, knocking each other, which results in them spreading throughout the room gradually, from high concentration to low concentration. Therefore, diffusion acts down (or along) a concentration gradient.
- [ATP (AQA)](https://thealevelbiologist.co.uk/atp-5/) - As I write this I am absolutely knackered which is juuuuuuuuust hilarious as I am about to cover ATP! Adenosine triphosphate is a small molecule whose constant breaking down and putting back together reactions form the basis of our biological processes which require chemical energy.
- [Proteins (CCEA)](https://thealevelbiologist.co.uk/proteins-3/) - This is what the generalised structure of an amino acid looks like (make sure you can draw this). If you’re wondering what this actually is, read on. The clues are in the name (as they usually are). AMINO – the H2N on the left hand side is an amino group. ACID – the COOH on the right hand side is a carboxylic acid group (simply an acid). The hydrogen (H) on the bottom is there all the time (just like the amino group and the acid group), while the R group is the variable which determines what particular amino acid this will be.
- [Nutrient Cycles (WJEC)](https://thealevelbiologist.co.uk/nutrient-cycles-3/) - Plants take up atmospheric CO2 to photosynthesise: the carbon in CO2 is transferred to the carbon in glucose. This carbon in glucose is either respired by the plant itself and released as CO2 back into the atmosphere, or is passed on to animals eating the plants. Here, it either gets released back as CO2 in respiration or becomes manure. But eventually, all the carbon not quickly released back into the atmosphere as CO2 will end up in the ground, for microorganisms to decompose.
- [Gene therapy (CCEA)](https://thealevelbiologist.co.uk/gene-therapy-2/) - Delivering DNA into cells for various purposes can be achieved via viruses which naturally can infect certain cells, as well as gene guns (biolistics) for plants. Gene therapy involves inserting a functional gene into a patient who lacks it, or needs supplementary support. This works for conditions which are caused by a single faulty gene rather than multiple genes. One problem associated with gene therapy is the immune reaction the body has to the virus. This may cause inflammation and other potentially serious side effects. Another issue is that of maintaining the effects of the healthy gene inserted into target cells.
- [Enzymes](https://thealevelbiologist.co.uk/enzymes-2/) - Enzymes are proteins which catalyse (speed up) metabolic reactions. Like all other catalysts (e.g. in chemistry), enzymes achieve this by lowering the activation energy (energy needed for a reaction to occur) of a reaction, by forming an enzyme-substrate complex.
- [Carbon cycle (CCEA)](https://thealevelbiologist.co.uk/carbon-cycle-2/) - At the heart of both the carbon and nitrogen cycles are microorganisms such as bacteria. These key nutrients pass from plants to animals through ingestion and digestion (eating!) in a very straightforward way, but what happens after those organisms die is a far more interesting tale.
- [Transport in plants (CCEA)](https://thealevelbiologist.co.uk/transport-in-plants-2/) - Why does water move inside the root? Simple: osmosis. The cell sap (i.e. cell juice) has a lower water potential than the fluid found in the soil, so the water in the soil kindly makes its way into the thirsty awaiting root. Once the water reaches the first cell in its path, the water potential of that cell is increased compared to the cell next to it. Therefore, water moves into the next cell, leaving…
- [Tissue fluid](https://thealevelbiologist.co.uk/tissue-fluid-2/) - Hydrostatic pressure determines the flow of these fluids between the different systems in a tissue. The oxygenated blood travelling through capillaries from arterioles has a high hydrostatic pressure, pushing the liquid outwards through small pores. This contains all the nutrients and gases cells need, which cross plasma membranes via diffusion or facilitated…
- [The genetic code (WJEC)](https://thealevelbiologist.co.uk/the-genetic-code-2/) - Having already covered the basics of DNA, let’s turn our attention to the principles which govern what actually happens to DNA and how this results in life being the way it is! DNA is a large molecule made up of variable bases (adenine, thymine, cytosine, guanine). The precise sequence and location of these bases determines what structure a second molecule, mRNA (messenger RNA) has once it’s “read” the template DNA. mRNA stands for messenger ribonucleic acid. DNA is deoxyribonucleic acid, and the only difference really is in the sugar in the backbone. A more important difference is that mRNA is single-stranded unlike double-stranded DNA.
- [Proteins (AQA)](https://thealevelbiologist.co.uk/proteins-2/) - The hydrogen (H) on the bottom is there all the time (just like the amino group and the acid group), while the R group is the variable which determines what particular amino acid this will be. For example, if the R group was a hydrogen, the amino acid would be glycine . The next diagram shows condensation, and the subsequent formation of a bond between two amino acids (any two).
- [Meiosis (CCEA)](https://thealevelbiologist.co.uk/meiosis-3/) - The first division is called meiosis I, and the second is called meiosis II …so far so easy? (it should be!) Cells resulting from meiosis are gametes such as egg cells and sperm cells, hence meiosis only occurs in sexually reproducing organisms. There are 2 key points about this:
- [Gene Technology (Edexcel)](https://thealevelbiologist.co.uk/gene-technology-2/) - If we had an enzyme which could reverse the transcription back into DNA, this time intron-free, that would be great. We do – it’s called reverse transcriptase and it produces DNA. This special case of DNA is called complementary DNA – cDNA. Some microorganisms have actually evolved enzymes whose job it is to invade a host and chop its DNA up at specific sequences. These enzymes are called restriction endonucleases. Each has its own short sequence which it recognises. There is a restriction endonuclease called CviQI which has the recognition site GTAC and cuts between G and T.
- [Biodiversity (WJEC)](https://thealevelbiologist.co.uk/biodiversity/) - Deforestation is the removal of trees in forests. and agriculture is the cultivation of useful plants to people which are often carefully selected for, and occupy a large area by themselves (like corn). It’s not hard to figure out the impact both have on species diversity. Deforestation practically removes many, whole trees, and with them goes the shelter and food source of many other organisms. A great reduction in species diversity can be expected as…
- [The Hardy-Weinberg principle (WJEC)](https://thealevelbiologist.co.uk/the-hardy-weinberg-principle/) - How could we keep track of the frequency of each allele for a given trait when we have a dominant-recessive interaction? More specifically, how could we account for the visible dominant traits as homozygous or heterozygous, since both look the same? This is where the Hardy-Weinberg principle comes in.
- [Synapse (WJEC)](https://thealevelbiologist.co.uk/synapse-2/) - Let’s just get the overall picture first: a signal may be transmitted from one neurone to another via axons and dendrites. A sending neurone passes the signal to a receiving neurone which may pass it on to another receiving neurone, thus becoming itself a sending neurone.
- [Succession (CCEA)](https://thealevelbiologist.co.uk/succession-2/) - The difference is that the above is primary i.e. it begins with totally barren land devoid of any nutrients or other abiotic factors (water, wind, temperature) conductive to life thriving, while secondary succession occurs after an already-thriving community has been wiped out by natural disasters such as a wild fire. Why make the distinction? In secondary succession, although it may look like all life is gone, the conditions needed for it to begin again more readily than in primary succession are there: plant seeds, plenty of nutrients in…
- [Mitosis (CCEA)](https://thealevelbiologist.co.uk/mitosis-3/) - Cell division requires the active remodelling of the cell’s cytoskeleton. The cytoskeleton is made of multiple kinds of protein that offer it the right structure and aid during the process of division. The centriole is a tubey spaghetti thing that aids in cell division when the duplicated chromosomes need to move into their subsequent new offspring cells from the parent cell (during mitosis).
- [Meiosis (WJEC)](https://thealevelbiologist.co.uk/meiosis-2/) - Gametes are genetically unlike one another – while cells in other tissues such as muscle or blood must be genetically identical to one another (clones), the very basis of sexual reproduction is genetic diversity. So somewhere in the process of division, something takes place which creates genetic diversity…
- [Light-Independent Reaction (WJEC)](https://thealevelbiologist.co.uk/light-independent-reaction-2/) - The LIR occurs in the stroma of chloroplasts (the space around thylakoid stacks which contains lots of enzymes involved in photosynthesis). All LIR events can be viewed as a cycle termed the Calvin cycle. The starting point is carbon dioxide, CO2, and the ending point is glucose (C6H12O6). Before the carbon atoms in CO2 can be incorporated into glucose, a series of events must take place.
- [Light-independent reaction (CCEA)](https://thealevelbiologist.co.uk/light-independent-reaction-3/) - The LIR occurs in the stroma of chloroplasts (the space around thylakoid stacks which contains lots of enzymes involved in photosynthesis). All LIR events can be viewed as a cycle termed the Calvin cycle. The starting point is carbon dioxide, CO2, and the ending point is glucose (C6H12O6). Before the carbon atoms in CO2 can be incorporated into glucose, a series of events must take place
- [Genetic fingerprinting (WJEC)](https://thealevelbiologist.co.uk/genetic-fingerprinting-2/) - Before the era of molecular biology, species were organised based on their physical characteristics. This, however, has turned out to be somewhat incorrect, as many lineages converge to the same outcome after initially being separated. For example, there are different species of flying squirrel which live on different continents. Their last common ancestor was not a flying squirrel, and following separation onto different parts of the world, they continued evolving separately.
- [Eukaryotic cell cycle and division](https://thealevelbiologist.co.uk/eukaryotic-cell-cycle-and-division/) - Bear in mind that some cells cease to divide any longer after a certain period of time, depending on cell type. If that’s the case, they are said to be in resting phase termed G0. Within the dividing cell, it starts with gap 1, G1, continues into the S phase (S is for Synthesis) where DNA replicates, followed by gap 2, G2, and ending with mitosis. G1 and G2 may sound like codes for some complex enzymes, but they are mere notations for gaps 1 and 2, which are just that: gaps between mitosis and DNA replication (in the S phase) respectively.
- [Epigenetics (CCEA)](https://thealevelbiologist.co.uk/epigenetics-2/) - Transcription can be inhibited by specific means. A common way is increased DNA methylation. The methyl (CH3) group acts as a tag on the DNA at various locations and prevents transcription that might’ve occurred otherwise. Another chemical modification that can induce epigenetic effects and control gene expression is histone deacetylation. Histones hold the DNA chromatin and help to compress it. In its acetylated state, it is relaxed and the DNA can be accessed by transcription machinery.
- [Ecosystems](https://thealevelbiologist.co.uk/ecosystems-2/) - A community is made up of the various populations in a habitat. So the summation of all the living things in a given area is called a community. What then is an ecosystem? An ecosystem comprises the community of living organisms in a habitat, together with all the non-living components such as water, soil, temperature, etc. called abiotic factors.
- [Causes of variation (CCEA)](https://thealevelbiologist.co.uk/causes-of-variation-2/) - DNA mutation occurs spontaneously and creates a direct change in the genetic material. Single bases may be changed, added or removed, or even large chunks of chromosomes can be swapped between them or duplicated. Whole chromosomes, too, can shift around. Mutations are a random occurrence during DNA replication and the rate of mutation is influenced by external factors such as UV radiation. There are different types of mutation…
- [Antibiotics (Edexcel)](https://thealevelbiologist.co.uk/antibiotics-2/) - They are substances which occur both naturally, as well as artificially as made by humans. The reason they are so widespread and important is because they solve a problem humanity has had for a very long time (i.e. forever). They are used to treat bacterial infections. Today that might seem like a small thing, yet around the globe millions of people still die all the time due to bacterial infections (e.g. pneumonia). It’s not a small thing, it is one of the greatest medical discoveries.
- [Polypeptide synthesis (CCEA)](https://thealevelbiologist.co.uk/polypeptide-synthesis-2/) - The complete set of genes in a cell is known as the genome while the full range of proteins a cell can make is the proteome. These are the steps that bridge these two realms. In a process called transcription, mRNA is formed based on DNA. The bases on the coding strand of DNA are transcribed into a new molecule, mRNA, which is synthesised by the enzyme RNA polymerase…
- [Plasma Membranes (CCEA)](https://thealevelbiologist.co.uk/plasma-membranes-3/) - Armed with the knowledge of lipids, as well as carbohydrates and proteins, we can now explore the structure of plasma membranes, specifically in the context of the fluid-mosaic model. Phospholipids have a hydrophilic (water loving) head, and hydrophobic (water repelling) tails. This results in the formation of a phospholipid bilayer (double layer), which forms the basis for the plasma membrane.
- [Mitosis (WJEC)](https://thealevelbiologist.co.uk/mitosis-2/) - Chromosomes begin to appear visible under a microscope due to chromatin (the coiled and yet-again coiled DNA fibre) condensing. Before this the DNA is not specifically distinguishable in the shape of chromosomes. This is a terrible word tangle so this is how it is. From a bowl of spaghetti (the nucleus) put the spaghetti in the shape of several chromosomes. Chromatin is the spaghetti initially, and chromosomes are the spaghetti still, just turned and twisted and distinguishable as individual stick-shaped objects. That is all, that’s all it is.
- [Mammalian circulation (WJEC)](https://thealevelbiologist.co.uk/mammalian-circulation-2/) - There are two types of circulation going on via the heart: pulmonary circulation and systemic circulation. Pulmonary circulation is a short-distance route between the heart and the lungs, where deoxygenated blood is taken to be replenished with oxygen. Although normally veins take blood away, and arteries take blood to, in the case of pulmonary circulation things are the opposite way around. The pulmonary vein brings freshly oxygenated blood into…
- [Light-dependent reaction (CCEA)](https://thealevelbiologist.co.uk/light-dependent-reaction-3/) - This takes place on the thylakoid membrane, and more specifically in a conglomerate of proteins/enzymes dedicated to this reaction, called photosystem II. It’s known as photoionisation. To maintain a fresh supply of dancing electrons, light also splits (photolysis) the H2O into… electrons, protons and… wait for it. Wait for it. Wait… Oxygen! So that’s how the oxygen by-product is…
- [Gene pool conservation](https://thealevelbiologist.co.uk/gene-pools-2/) - Conservation of species can take place in their original environment (in-situ) or outside of it (ex-situ). Examples of ex-situ conservation are zoos and seed banks. Zoos host animals outside of their original environment, under highly controlled conditions. Animals are no longer subject to predation, don’t have to provide for themselves, and have access to advanced healthcare.
- [Gas exchange (AQA)](https://thealevelbiologist.co.uk/gas-exchange-2-2/) - The distance between an oxygen molecule which must be taken in, and the place it must get to within a bacterium is short enough for diffusion to be a viable way of exchanging substances with the environment, without the need for additional structures. In mammals, for example, oxygen cannot simply diffuse into our bodies. We are too large, have a low surface area to volume ratio, hence the diffusion pathway is too long. The only way we can achieve gas exchange is through our lungs which provide a large surface area and alveoli with short diffusion pathways.
- [DNA and protein synthesis (AQA)](https://thealevelbiologist.co.uk/dna-and-protein-synthesis-2/) - The complete set of genes in a cell is known as the genome while the full range of proteins a cell can make is the proteome. These are the steps that bridge these two realms. Proteins are made up of amino acids linked by peptide bonds, therefore a protein may be referred to as a polypeptide (of course, some proteins such as haemoglobin have extra bits to them). All are encoded for by the information stored in DNA. Let’s see how exactly this happens.
- [Cholera (WJEC)](https://thealevelbiologist.co.uk/cholera-2/) - Cholera is an infectious disease caused by Vibrio cholerae, which is a major cause of death in areas of the world where a proper infrastructure for good sanitation doesn’t exist. Bacteria are ingested by consuming contaminated water and food. The water becomes contaminated when a person with the disease (which causes severe diarrhoea) produces the faeces which then carry the bacteria in the water supply.
- [Active Transport (CCEA)](https://thealevelbiologist.co.uk/active-transport-3/) - Unlike diffusion, osmosis and facilitated diffusion, active transport requires energy in the form of ATP (adenosine triphosphate), and moves substances against a concentration gradient (from a lower concentration to a higher concentration). This process is essential in removing of all toxins from the body, as well as the movement of rare chemicals.
- [Homeostasis](https://thealevelbiologist.co.uk/homeostasis-2/) - The internal environment of our bodies is constantly kept within strict limits. Take for example temperature. It must be a challenge keeping our fleshy selves at 37°C while the outside fluctuates wildly! Or how about blood glucose concentration? From a physiological viewpoint, think of enzyme activity. Its sensitivity to both temperature and pH means that the only conditions of optimal function will be strictly defined. Lots of enzymes denature past 40°C and are inactivated below 35°C.
- [Pathogens (WJEC)](https://thealevelbiologist.co.uk/pathogens-2/) - In the field of disease, pathogens are organisms found at the crossroads between species and their way of surviving and reproducing. At these specific crossroads, the actions of one organism hurt the other. The pathogenic organism is the one inflicting disease upon the victim. The mechanism of transmission for pathogens can include carriers and disease reservoirs. Carriers are infected with the pathogen but do not suffer from disease as a result of infection.
- [Photosynthesis (AQA)](https://thealevelbiologist.co.uk/photosynthesis-2/) - Photosynthesis is the process by which most plants as well as other organisms e.g. photosynthetic bacteria obtain their energy (glucose) ultimately in the form of ATP upon respiration. So photosynthesis produces the glucose, and the glucose is the substrate for respiration which produces ATP.
- [Photosynthesis (WJEC)](https://thealevelbiologist.co.uk/photosynthesis-4/) - The general balanced reaction for photosynthesis is: H2O + CO2 + energy –> C6H12O6 + O2 …where water, carbon dioxide and energy are the starting materials, and glucose and oxygen the products. Here, glucose is the key product because it is the complex organic molecule made from simple inorganic reactants.
- [Plasma membranes (WJEC)](https://thealevelbiologist.co.uk/plasma-membranes-2/) - The name of fluid-mosaic model comes from: Fluid = the arrangement of proteins contained in the membrane is always changing, and Mosaic = the proteins present are spread around in a mosaic-like fashion. It’s pretty isn’t it? The proteins are crucial to cell communication as well as the selective permeability of the membrane. The glycoprotein (sugars/carbohydrates attached to a protein) side chains act as…
- [Population growth (CCEA)](https://thealevelbiologist.co.uk/population-growth/) - There are several predictable population growth phases, typically seen in lab-grown microorganisms in controlled environments. The lag phase represents the beginning of their growth. Once they get adjusted to their new environment and start thriving, they are ready to divide. This takes place actively during the log phase when their growth is exponential (because 2 cells become 4, and 4 become 8, and 8 become 16). Once their expansion into the media has reached its maximum potential, and they begin to run out of space and nutrients, they reach the stationary phase where division halts.
- [Surface area to volume ratio (CCEA)](https://thealevelbiologist.co.uk/surface-area-to-volume-ratio-2/) - Two properties are important to consider here: the volume of an organism, and the surface area of an organism. The volume is what determines the amount of substances which need exchanging, while the surface area determines the amount which can be exchanged. Surface area describes the number of cells in direct contact with the environment. Volume describes the space occupied by all metabolically active cells.
- [The genetic code (CCEA)](https://thealevelbiologist.co.uk/the-genetic-code-3/) - DNA is deoxyribonucleic acid, and the only difference really is in the sugar in the backbone. A more important difference is that mRNA is single-stranded unlike double-stranded DNA. Additionally, instead of the base thymine, mRNA uses uracil. So while adenine pairs up with thymine in DNA, it pairs up with uracil in mRNA. Knowing that, the mRNA derived from this DNA (looking at the top strand) would be as follows
- [Inheritance (AQA)](https://thealevelbiologist.co.uk/inheritance-3/) - The genotype refers to the physical constitution of a little part of DNA. Its expression, however (that is what protein a gene encodes, and what that protein ends up doing in the organism) is a separate entity which is subject to environmental influence. This is called the phenotype. Humans have 2 sets of chromosomes, so for each distinct chromosome e.g. chromosome 1, there are two copies. How do the same genes on both homologous chromosomes interact if they result in different phenotypes?
- [Inheritance (CCEA)](https://thealevelbiologist.co.uk/inheritance-4/) - The entirety of genetic material in an organism is called a genotype. It can also refer to specific things, like a genotype for a certain trait in a given organism. The genotype refers to the physical constitution of a little part of DNA. Its expression, however (that is what protein a gene encodes, and what that protein ends up doing in the organism) is a separate entity which is subject to environmental influence. This is called the phenotype.
- [Gene pools (CCEA)](https://thealevelbiologist.co.uk/gene-pools-3/) - The sum of all present alleles for a given gene in a given population is known as the gene pool. In the wild, each species may exist as one population or multiple populations. Different populations correspond to defined areas – habitats. This is essentially a way of thinking about all the individuals in a population contributing their alleles towards the overall allele frequency.
- [Diffusion, facilitated diffusion and osmosis](https://thealevelbiologist.co.uk/diffusion/) - Conversely, small molecules can cross the membrane barrier, alongside molecules with no charge (nonionised) as well as lipophilic (hydrophobic) molecules. It’s important to understand the role of microvilli. These are elongations of plasma membrane which increase the surface area available for reaction or absorption. Diffusion = the spread of particles from a region of higher concentration to a region of lower concentration, until the particles are…
- [Cell Cycle (WJEC)](https://thealevelbiologist.co.uk/cell-cycle-3/) - G1 and G2 may sound like codes for some complex enzymes, but they are mere notations for gaps 1 and 2, which are just that: gaps between mitosis and DNA replication (in the S phase) respectively. G1 through to G2 – that’s G1, S phase and G2 – are all stages which collectively are known as interphase. Inter = between; phase = …phase, so interphase is just the stage between a cell’s creation and that cell’s division by mitosis.
- [Carbohydrates (Edexcel)](https://thealevelbiologist.co.uk/carbohydrates-2/) - Glucose is a key carbohydrate in biology because it is the preferred fuel that provides energy during cellular respiration as well as the building block for complex polysaccharides and other compounds that use it such as glycoproteins. As a monomer, it is small and…
- [Carbohydrates (AQA)](https://thealevelbiologist.co.uk/carbohydrates-3/) - So the monosaccharide alpha glucose (commonly, just glucose) somehow becomes a polysaccharide, This is achieved by condensation reactions, and the bonds formed are called glycosidic bonds. You should be able to draw this. The resulting molecule, maltose, is a disaccharide (two monomers). If you keep adding glucose molecules to the chain, you get… *drum roll please* …starch. Starch is made up of multiple (very many indeed) monomers, so it is a polymer i.e. it is made of multiple monosaccharides, so it is a polysaccharide.
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- [](https://thealevelbiologist.co.uk/circulation/) - In my quest to find a suitable diagram for the heart, this is what I found. Definitely use your textbook as a guide on this. It only takes a google search to realise the ridiculous number of variations of diagrams for the heart and different annotations. You need to be able to sketch a heart and label the main veins, valves, arteries and aorta, and the ventricles and atria.
- [](https://thealevelbiologist.co.uk/the-compensation-point/) - The point at which photosynthesis and respiration are taking place at the same rate is called the compensation point.
- [](https://thealevelbiologist.co.uk/plant-cells/) - The example for this topic will be (as per the specification) a palisade cell from a leaf. They are just beneath the cuticle – very close to the leaf surface. You need to be familiar with the appearance of a palisade cell under an optical microscope. Without further ado, I present to you the stunning palisade cell:
- [](https://thealevelbiologist.co.uk/legacy-topics/principles-negative-feedback/) - The operation of an oven is an easy example of negative feedback acting both ways, which is how it usually acts. That means that there are deviations in two opposing directions. If an oven is set at 220°C, both a decrease and an increase in temperature is a deviation. So if the temperature drops or rises, a sensor picks that up and commands the heater to turn on or off.
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- [???? Cell Cycle](https://thealevelbiologist.co.uk/cell-cycle-2/) - The cell cycle refers to the distinct stages through which a cell goes, from the moment it becomes a cell to the moment it divides to result in 2 separate cells. It starts with gap 1, G1, continues into the S phase (S is for Synthesis) where DNA replicates, followed by gap 2, G2, and ending with mitosis.
- [⚙️ ATP (CCEA)](https://thealevelbiologist.co.uk/atp-4/) - When the hydrolysis of ATP (via the enzyme ATP hydrolase) is coupled to other reactions requiring energy, it enables these processes to take place. The inorganic phosphate released can itself take part in a further phosphorylation reaction with another chemical, often increasing its…
- [⛈️ Nitrogen cycle (CCEA)](https://thealevelbiologist.co.uk/nitrogen-cycle-2/) - Nitrogen is also a key element that makes up DNA and proteins. It is present in its cycle in various forms including nitrogen gas which makes up the biggest part of the air in the Earth’s atmosphere, ammonia, nitrites and nitrates in the soil, and of course in all the waste products of living things. Microorganisms also play a key role here in decomposing these materials and producing the intermediary nitrates. Following a series of reactions, nitrogen from these sources ends up back into the atmosphere.
- [☁️ Gas Exchange (CCEA)](https://thealevelbiologist.co.uk/gas-exchange-3/) - Plants require gas exchange to intake carbon dioxide and make glucose via photosynthesis, and to release oxygen as a byproduct. Animal whose cells respire aerobically require oxygen to produce energy for their metabolism, while releasing carbon dioxide which is the byproduct (yes, photosynthesis and respiration are converse processes; bear in mind plants do carry out both).
- [✈️ Mass transport (CCEA)](https://thealevelbiologist.co.uk/mass-transport-2/) - But how does the oxygen acquired by the lungs actually reach every single cell of the body? A network of sorts is needed to do that. Many bigger and smaller tubes would come in handy. They would form like a… circulatory system. Oh wait, that’s precisely what mammals have: a circulatory system made of arteries, veins, capillaries, etc. Plants, too, have a vascular (tubular) system. It is made of xylems and phloems. The key thing is that this circulation of a large amount of substances via a system of transportation is called mass flow, hence mass transport.
- [⚙️ ATP (WJEC)](https://thealevelbiologist.co.uk/atp-3/) - ATP is adenosine triphosphate, a nucleotide involved in metabolism and many biological processes (the molecular energy currency). Nucleotides are also the basic units involved in other central molecules such as DNA and RNA which carry genetic information in cells. A nucleotide is a molecule composed of a pentose sugar, an organic base and at least one phosphate group.
- [✈️ Active Transport (WJEC)](https://thealevelbiologist.co.uk/active-transport-2/) - A lot of molecules essential to life are too large to simply cross the plasma membrane, or even pass through protein channels embedded within. The way these are transported is by being enveloped in lipid bubbles that join with the main membrane and open up to release the content to the other side of the membrane (pinocytosis – a form of endocytosis). Conversely, a bubble, called vesicle, already in the cytoplasm can merge with the plasma membrane and release its content on the outside (exocytosis). This process does use energy (ATP, see next headings).
- [⛅ Light-Dependent Reaction (WJEC)](https://thealevelbiologist.co.uk/light-dependent-reaction-2/) - As in the overview of photosynthesis, the light-dependent reactions utilise light energy to convert it into more usable chemical energy. So naturally, it starts with light. This is the brief sequence of events: 1. The electrons present in the chlorophyll of the plant’s chloroplasts are brought to a higher energy level (they enjoy dancing more) by light energy
- [⛈️ Nutrient Cycles](https://thealevelbiologist.co.uk/nutrient-cycles-2/) - At the heart of both the carbon and nitrogen cycles are microorganisms such as bacteria. These key nutrients pass from plants to animals through ingestion and digestion (eating!) in a very straightforward way, but what happens after those organisms die is a far more interesting tale.
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- [Aerobic and anaerobic respiration](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-1/aerobic-and-anaerobic-respiration/)
- [Anaerobic Respiration](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-1/anaerobic-respiration-2/)
- [⚙️ Cellular Respiration](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-1/cellular-respiration/)
- [⚙️ Cell respiration](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-2/cell-respiration/)
- [Cell respiration](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-2/cell-respiration-2/)
- [Cellular respiration](https://thealevelbiologist.co.uk/exam-boards/sat/module-1/cellular-respiration-2/)
- [DNA Replication](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-1/dna-replication-2/)
- [Energy and Ecosystems](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-1/energy-and-ecosystems/)
- [Nutrient Cycles](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-1/nutrient-cycles/)
- [Survival and response](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-2/survival-and-response/)
- [Receptors](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-2/receptors/)
- [Control of Heart Rate](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-2/control-of-heart-rate/)
- [Synaptic Transmission](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-2/synaptic-transmission/)
- [Skeletal muscles are stimulated to contract by nerves and act as effectors](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-2/skeletal-muscles-are-stimulated-to-contract-by-nerves-and-act-as-effectors/)
- [Control of Blood Glucose Concentration](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-2/control-of-blood-glucose-concentration/)
- [Inheritance](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-3/inheritance/)
- [Populations](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-3/populations/)
- [Evolution may lead to speciation](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-3/evolution-may-lead-to-speciation/)
- [Populations in ecosystems](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-3/populations-in-ecosystems/)
- [Alteration of the sequence of bases in DNA can alter the structure of proteins](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-4/alteration-of-the-sequence-of-bases-in-dna-can-alter-the-structure-of-proteins/)
- [Most of a Cell's DNA is not Translated](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-4/most-of-a-cells-dna-is-not-translated/)
- [Regulation of Transcription and Translation](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-4/regulation-of-transcription-and-translation/)
- [Gene expression and cancer](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-4/gene-expression-and-cancer/)
- [Using genome projects](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-4/using-genome-projects/)
- [Recombinant DNA Technology](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-4/recombinant-dna-technology/)
- [Differences in DNA between individuals of the same species can be exploited for identification and diagnosis of heritable conditions](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-4/differences-in-dna-between-individuals-of-the-same-species-can-be-exploited-for-identification-and-diagnosis-of-heritable-conditions/)
- [Genetic Fingerprinting](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-4/genetic-fingerprinting/)
- [Negative Feedback](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-1/negative-feedback/)
- [Kidney Function](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-1/kidney-function/)
- [Principles of immunity](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-2/principles-of-immunity/)
- [Transplantation and immunosuppression](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-2/transplantation-and-immunosuppression/)
- [Plant hormones](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-3/plant-hormones/)
- [Neurones](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-3/neurones/)
- [Action potential](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-3/action-potential/)
- [Mammalian vision](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-3/mammalian-vision/)
- [Muscle contraction](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-3/muscle-contraction/)
- [Population growth](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-4/population-growth-2/)
- [Communities and ecosystems](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-4/communities-and-ecosystems/)
- [Succession](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-4/succession-2/)
- [Carbon cycle](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-4/carbon-cycle/)
- [Nitrogen cycle](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-4/nitrogen-cycle/)
- [Cell Specialisation](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-7/cell-specialisation/)
- [Ileum structure and function](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-7/ileum-structure-and-function/)
- [Absorption by the epithelium](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-7/absorption-by-the-epithelium/)
- [Structure and function of a mesophytic leaf](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-7/structure-and-function-of-a-mesophytic-leaf/)
- [Chromosomes](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-6/chromosomes/)
- [Mitosis](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-6/mitosis-2/)
- [Meiosis](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-6/meiosis-2/)
- [Diffusion, facilitated diffusion and osmosis](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-5/diffusion-facilitated-diffusion-and-osmosis/)
- [Active Transport](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-5/active-transport-2/)
- [Cell Structure](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-4/cell-structure/)
- [Plasma Membranes](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-4/plasma-membranes-2/)
- [Microscopy](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-4/microscopy/)
- [Structure of bacteriophage and of HIV](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-3/structure-of-bacteriophage-and-of-hiv/)
- [Enzyme Structure](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-2/enzyme-structure/)
- [Enzyme Function](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-2/enzyme-function/)
- [Immobilised enzymes in biotech](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-2/immobilised-enzymes-in-biotech/)
- [Water](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-1/water-3/)
- [Inorganic Ions](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-1/inorganic-ions-3/)
- [Carbohydrates](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-1/carbohydrates-2/)
- [Lipids](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-1/lipids-3/)
- [Proteins](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-1/proteins-2/)
- [DNA](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-1/dna/)
- [The nature of ecosystems](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-6/the-nature-of-ecosystems/)
- [Energy transfer through ecosystems](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-6/energy-transfer-through-ecosystems/)
- [Changes in ecosystems](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-6/changes-in-ecosystems/)
- [Human effects on ecosystems](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-6/human-effects-on-ecosystems/)
- [Homeostasis](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-5/homeostasis/)
- [Chemical Control in Mammals](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-5/chemical-control-in-mammals/)
- [Chemical Control in Plants](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-5/chemical-control-in-plants/)
- [Structure and function of the mammalian nervous system](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-5/structure-and-function-of-the-mammalian-nervous-system/)
- [Nervous transmission](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-5/nervous-transmission/)
- [Effects of drugs on the nervous system](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-5/effects-of-drugs-on-the-nervous-system/)
- [Detection of light by mammals](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-5/detection-of-light-by-mammals/)
- [Control of heart rate in mammals](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-5/control-of-heart-rate-in-mammals/)
- [Origins of genetic variation](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-4/origins-of-genetic-variation/)
- [Transfer or genetic information](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-4/transfer-or-genetic-information/)
- [Gene Pools](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-4/gene-pools-2/)
- [Using gene sequencing](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-3/using-gene-sequencing/)
- [Factors affecting gene expression](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-3/factors-affecting-gene-expression/)
- [Stem Cells](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-3/stem-cells/)
- [Gene Technology](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-3/gene-technology/)
- [Microbial Techniques](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-2/microbial-techniques/)
- [Bacteria as pathogens](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-2/bacteria-as-pathogens/)
- [Antibiotics](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-2/antibiotics-2/)
- [Problems of controlling endemic diseases](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-2/problems-of-controlling-endemic-diseases/)
- [Response to infection](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-2/response-to-infection/)
- [Aerobic Respiration](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-1/aerobic-respiration/)
- [Oxidative Phosphorylation](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-1/oxidative-phosphorylation/)
- [Photosynthetic pigments](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-1/photosynthetic-pigments/)
- [Carbohydrates](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-1/carbohydrates-3/)
- [Lipids](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-1/lipids-4/)
- [Proteins](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-1/proteins-3/)
- [DNA and Protein Synthesis](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-1/dna-and-protein-synthesis-2/)
- [Inorganic Ions](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-1/inorganic-ions-4/)
- [Water](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-1/water-4/)
- [Viruses](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-2/viruses/)
- [Eukaryotic cell cycle and division](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-2/eukaryotic-cell-cycle-and-division/)
- [Sexual reproduction in mammals](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-2/sexual-reproduction-in-mammals/)
- [Sexual reproduction in plants](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-2/sexual-reproduction-in-plants/)
- [Classification](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-3/classification/)
- [Natural selection](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-3/natural-selection/)
- [Biodiversity](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-3/biodiversity-2/)
- [Surface area to volume ratio](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-4/surface-area-to-volume-ratio-2/)
- [Cell transport mechanisms](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-4/cell-transport-mechanisms/)
- [Gas exchange](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-4/gas-exchange-3/)
- [Circulation](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-4/circulation/)
- [Transport of gases in the blood](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-4/transport-of-gases-in-the-blood/)
- [Transport of materials between the circulatory system and cells](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-4/transport-of-materials-between-the-circulatory-system-and-cells/)
- [Transport in plants](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-4/transport-in-plants-2/)
- [Metabolism and exercise](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-1/metabolism-and-exercise/)
- [Fertility and assisted reproduction](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-1/fertility-and-assisted-reproduction/)
- [The effects of ageing on the reproductive system](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-1/the-effects-of-ageing-on-the-reproductive-system/)
- [Photosynthesis, food production and management of the environment](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-1/photosynthesis-food-production-and-management-of-the-environment/)
- [The impact of population increase](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-1/the-impact-of-population-increase/)
- [Plant reproduction](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-1/plant-reproduction/)
- [Patterns of inheritance](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-2/patterns-of-inheritance/)
- [Population genetics and epigenetics](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-2/population-genetics-and-epigenetics/)
- [Gene technologies](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-2/gene-technologies/)
- [The nervous system and the identification and consequences of damage](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-2/the-nervous-system-and-the-identification-and-consequences-of-damage/)
- [Monitoring visual function](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-2/monitoring-visual-function/)
- [The effect of ageing on the nervous system](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-2/the-effect-of-ageing-on-the-nervous-system/)
- [The hormonal control of blood glucose and the management of diabetes](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-2/the-hormonal-control-of-blood-glucose-and-the-management-of-diabetes/)
- [Kidney functions and malfunctions](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-2/kidney-functions-and-malfunctions/)
- [Practical skills assessed in a written examination](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-1/practical-skills-assessed-in-a-written-examination/)
- [Practical skills assessed in the practical endorsement](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-1/practical-skills-assessed-in-the-practical-endorsement/)
- [Cells and microscopy](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-2/cells-and-microscopy/)
- [Water and its importance in plants and animals](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-2/water-and-its-importance-in-plants-and-animals/)
- [Proteins and Enzymes](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-2/proteins-and-enzymes/)
- [Nucleic Acids](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-2/nucleic-acids/)
- [The heart and monitoring heart function](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-2/the-heart-and-monitoring-heart-function/)
- [Transport systems in mammals](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-2/transport-systems-in-mammals/)
- [Gas exchange in mammals and plants](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-2/gas-exchange-in-mammals-and-plants/)
- [Transport systems in plants](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-2/transport-systems-in-plants/)
- [The developing cell: cell division and cell differentiation](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-3/the-developing-cell-cell-division-and-cell-differentiation/)
- [The developing individual: meiosis, growth and development](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-3/the-developing-individual-meiosis-growth-and-development/)
- [The development of species: evolution and classification](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-3/the-development-of-species-evolution-and-classification/)
- [Pathogenic microorganisms](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-3/pathogenic-microorganisms/)
- [The immune system](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-3/the-immune-system/)
- [Controlling communicable diseases](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-3/controlling-communicable-diseases/)
- [The cellular basis of cancer and treatment](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-3/the-cellular-basis-of-cancer-and-treatment/)
- [Respiratory diseases and treatment](https://thealevelbiologist.co.uk/exam-boards/ocr-as/module-3/respiratory-diseases-and-treatment/)
- [The structure of DNA](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-1/the-structure-of-dna/)
- [Replication of DNA](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-1/replication-of-dna-2/)
- [Control of gene expression](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-1/control-of-gene-expression/)
- [Cellular differentiation](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-1/cellular-differentiation/)
- [The structure of the genome](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-1/the-structure-of-the-genome/)
- [Evolution](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-1/evolution/)
- [Genomic sequencing](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-1/genomic-sequencing/)
- [Metabolic pathways and their control](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-2/metabolic-pathways-and-their-control/)
- [Metabolic rate](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-2/metabolic-rate/)
- [Metabolism in conformers and regulators](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-2/metabolism-in-conformers-and-regulators/)
- [Metabolism and adverse conditions](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-2/metabolism-and-adverse-conditions/)
- [Environmental control of metabolism](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-2/environmental-control-of-metabolism/)
- [Genetic control of metabolism](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-2/genetic-control-of-metabolism/)
- [Plant and animal breeding](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-3/plant-and-animal-breeding/)
- [Crop protection](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-3/crop-protection/)
- [Animal welfare](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-3/animal-welfare/)
- [Symbiosis](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-3/symbiosis/)
- [Social behaviour](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-3/social-behaviour/)
- [Mass extinction and biodiversity](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-3/mass-extinction-and-biodiversity/)
- [Threats to biodiversity](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-3/threats-to-biodiversity/)
- [Laboratory techniques for biologists](https://thealevelbiologist.co.uk/exam-boards/scottish-advanced-higher/module-1/laboratory-techniques-for-biologists/)
- [Proteins](https://thealevelbiologist.co.uk/exam-boards/scottish-advanced-higher/module-1/proteins-4/)
- [Membrane proteins](https://thealevelbiologist.co.uk/exam-boards/scottish-advanced-higher/module-1/membrane-proteins/)
- [Detecting and amplifying an environmental stimulus](https://thealevelbiologist.co.uk/exam-boards/scottish-advanced-higher/module-1/detecting-and-amplifying-an-environmental-stimulus/)
- [Communication within multicellular organisms](https://thealevelbiologist.co.uk/exam-boards/scottish-advanced-higher/module-1/communication-within-multicellular-organisms/)
- [Protein control of cell division](https://thealevelbiologist.co.uk/exam-boards/scottish-advanced-higher/module-1/protein-control-of-cell-division/)
- [Organisms](https://thealevelbiologist.co.uk/exam-boards/scottish-advanced-higher/module-2/organisms/)
- [Variation and sexual reproduction](https://thealevelbiologist.co.uk/exam-boards/scottish-advanced-higher/module-2/variation-and-sexual-reproduction/)
- [Sex and behaviour](https://thealevelbiologist.co.uk/exam-boards/scottish-advanced-higher/module-2/sex-and-behaviour/)
- [Parasitism](https://thealevelbiologist.co.uk/exam-boards/scottish-advanced-higher/module-2/parasitism/)
- [Scientific principles and process](https://thealevelbiologist.co.uk/exam-boards/scottish-advanced-higher/module-3/scientific-principles-and-process/)
- [Experimentation](https://thealevelbiologist.co.uk/exam-boards/scottish-advanced-higher/module-3/experimentation/)
- [Critical evaluation of biological research](https://thealevelbiologist.co.uk/exam-boards/scottish-advanced-higher/module-3/critical-evaluation-of-biological-research/)
- [Response to stimuli and the spinal cord](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-8/response-to-stimuli-and-the-spinal-cord/)
- [Mammalian kidney structure and function](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-7/mammalian-kidney-structure-and-function/)
- [Kidney failure](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-7/kidney-failure/)
- [Gene pool conservation](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-6/gene-pool-conservation/)
- [Agriculture](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-6/agriculture/)
- [Politics and the environment](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-6/politics-and-the-environment/)
- [Population growth](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-5/population-growth/)
- [Sampling Organisms](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-5/sampling-organisms/)
- [Ecosystems](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-5/ecosystems/)
- [Biomass transfer](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-5/biomass-transfer/)
- [Succession](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-5/succession/)
- [Nutrient cycles](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-5/nutrient-cycles-2/)
- [Carbon Cycle](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-5/carbon-cycle-2/)
- [Nitrogen cycle](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-5/nitrogen-cycle-3/)
- [Bacterial classification](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-4/bacterial-classification/)
- [Culturing microorganisms](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-4/culturing-microorganisms/)
- [Optimising and analysing growth](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-4/optimising-and-analysing-growth/)
- [Lipids and amino acids in respiration](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-3/lipids-and-amino-acids-in-respiration/)
- [Light-Dependent Reaction](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-2/light-dependent-reaction/)
- [Light-Independent Reaction](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-2/light-independent-reaction/)
- [Limiting factors in photosynthesis](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-2/limiting-factors-in-photosynthesis/)
- [Fertilisers](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-2/fertilisers/)
- [Inorganic Ions](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-1/inorganic-ions-2/)
- [Water](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-1/water-2/)
- [Carbohydrate structure and function](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-1/carbohydrate-structure-and-function/)
- [Starch, Cellulose and Chitin](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-1/starch-cellulose-and-chitin/)
- [Lipids](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-1/lipids-2/)
- [Protein Structure](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-1/protein-structure/)
- [Eukaryotic Cells](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-2/eukaryotic-cells/)
- [Prokaryotic Cells and Viruses](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-2/prokaryotic-cells-and-viruses/)
- [Cell differences and microscopy](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-2/cell-differences-and-microscopy/)
- [Organisation under the microscope: cells, tissues, organs](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-2/organisation-under-the-microscope-cells-tissues-organs/)
- [Plasma membranes](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-3/plasma-membranes/)
- [Passive Transport](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-3/passive-transport/)
- [Active Transport](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-3/active-transport/)
- [Enzyme structure and action](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-4/enzyme-structure-and-action/)
- [Factors affecting enzyme function](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-4/factors-affecting-enzyme-function/)
- [Immobilised enzymes in industry](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-4/immobilised-enzymes-in-industry/)
- [ATP](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-5/atp-2/)
- [DNA Structure](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-5/dna-structure/)
- [DNA Replication](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-5/dna-replication/)
- [The genetic code](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-5/the-genetic-code/)
- [Polypeptide synthesis and processing](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-5/polypeptide-synthesis-and-processing/)
- [Cell Cycle](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-6/cell-cycle/)
- [Mitosis](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-6/mitosis/)
- [Meiosis](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-1/module-6/meiosis/)
- [Classification of organisms](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-1/classification-of-organisms/)
- [Kingdoms: Prokaryotae, Protoctista, Plantae, Fungi, Animalia](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-1/kingdoms-prokaryotae-protoctista-plantae-fungi-animalia/)
- [Genetic fingerprinting](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-1/genetic-fingerprinting-2/)
- [Biodiversity](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-1/biodiversity/)
- [Measuring biodiversity and natural selection](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-1/measuring-biodiversity-and-natural-selection/)
- [Adaptation](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-1/adaptation/)
- [Gas Exchange Adaptations](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-2/gas-exchange-adaptations/)
- [Insect and fish gas exchange](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-2/insect-and-fish-gas-exchange/)
- [Human gas exchange](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-2/human-gas-exchange/)
- [Structure of the angiosperm leaf](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-2/structure-of-the-angiosperm-leaf/)
- [Earthworm, insect, fish and mammal vascular systems](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-3/earthworm-insect-fish-and-mammal-vascular-systems/)
- [Mammalian circulation](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-3/mammalian-circulation/)
- [Haemoglobin](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-3/haemoglobin/)
- [Tissue fluid](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-3/tissue-fluid/)
- [Plant transport](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-3/plant-transport/)
- [Types of nutrition](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-4/types-of-nutrition/)
- [Unicellular nutrition in Amoeba and multicellular nutrition in Hydra](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-4/unicellular-nutrition-in-amoeba-and-multicellular-nutrition-in-hydra/)
- [Human gut adaptations and digestion](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-4/human-gut-adaptations-and-digestion/)
- [Herbivore and carnivore adaptations](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-4/herbivore-and-carnivore-adaptations/)
- [Parasites](https://thealevelbiologist.co.uk/exam-boards/wjec-as-unit-2/module-4/parasites/)
- [Human Genome Project and its implications](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-5/human-genome-project-and-its-implications/)
- [PCR, gel electrophoresis and GMOs](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-5/pcr-gel-electrophoresis-and-gmos/)
- [Genomics, gene therapy and stem cells](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-5/genomics-gene-therapy-and-stem-cells/)
- [Causes of variation between individuals](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-4/causes-of-variation-between-individuals/)
- [Gene pool](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-4/gene-pool/)
- [The Hardy-Weinberg principle](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-4/the-hardy-weinberg-principle-2/)
- [Speciation and natural selection](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-4/speciation-and-natural-selection/)
- [Alleles and Mendelian inheritance](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-3/alleles-and-mendelian-inheritance/)
- [Chi squared test](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-3/chi-squared-test/)
- [Gene mutation in sickle cell anaemia and chromosome mutation in Down's syndrome](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-3/gene-mutation-in-sickle-cell-anaemia-and-chromosome-mutation-in-downs-syndrome/)
- [Epigenetics](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-3/epigenetics/)
- [Flowers, pollen and ovules](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-2/flowers-pollen-and-ovules/)
- [Pollination and double-fertilisation](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-2/pollination-and-double-fertilisation/)
- [Seed, fruit, germination and the hormone gibberellin](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-2/seed-fruit-germination-and-the-hormone-gibberellin/)
- [Menstruation, gestation and lactation](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-1/menstruation-gestation-and-lactation/)
- [Human brain structure and function](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-3/human-brain-structure-and-function/)
- [Hypothalamus](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-3/hypothalamus/)
- [Sensory and motor areas in the cortex](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-3/sensory-and-motor-areas-in-the-cortex/)
- [Language and speech](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-3/language-and-speech/)
- [Brain study techniques](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-3/brain-study-techniques/)
- [Brain development and neuroplasticity](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-3/brain-development-and-neuroplasticity/)
- [Gene expression and the brain](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-3/gene-expression-and-the-brain/)
- [Reflex, taxis and kinesis](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-3/reflex-taxis-and-kinesis/)
- [Learned behaviour](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-3/learned-behaviour/)
- [Social groups](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-3/social-groups/)
- [Insect social structure](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-3/insect-social-structure/)
- [Dominance hierarchies in vertebrates](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-3/dominance-hierarchies-in-vertebrates/)
- [Courtship behaviour and sexual selection](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-3/courtship-behaviour-and-sexual-selection/)
- [Bone components and their function](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-2/bone-components-and-their-function/)
- [Bone disease](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-2/bone-disease/)
- [Skeletal muscle](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-2/skeletal-muscle/)
- [Skeleton function](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-2/skeleton-function/)
- [Sliding filament theory](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-2/sliding-filament-theory/)
- [Muscle contraction fuels and conditions](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-2/muscle-contraction-fuels-and-conditions/)
- [The skeleton and fractures](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-2/the-skeleton-and-fractures/)
- [Vertebrae and deformities](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-2/vertebrae-and-deformities/)
- [Joint types](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-2/joint-types/)
- [Forelimb muscle action and the role of tendons](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-2/forelimb-muscle-action-and-the-role-of-tendons/)
- [Synovial joint structure](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-2/synovial-joint-structure/)
- [Joints as levers](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-2/joints-as-levers/)
- [Osteoarthritis and rheumatoid arthritis](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-2/osteoarthritis-and-rheumatoid-arthritis/)
- [Cholera](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-1/cholera/)
- [Tuberculosis](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-1/tuberculosis/)
- [Smallpox](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-1/smallpox/)
- [Influenza](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-1/influenza/)
- [Malaria](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-1/malaria/)
- [Virus pathogenicity and mode of reproduction](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-1/virus-pathogenicity-and-mode-of-reproduction/)
- [Antibiotics](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-1/antibiotics/)
- [Immune System](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-1/immune-system/)
- [Vaccination](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-1/vaccination/)
- [Overview](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-2/overview/)
- [Light-dependent reaction](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-2/light-dependent-reaction-2/)
- [Light-independent reaction](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-2/light-independent-reaction-2/)
- [Limiting factors](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-2/limiting-factors/)
- [The genetic code](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-3/the-genetic-code-2/)
- [Polypeptide synthesis](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-3/polypeptide-synthesis/)
- [Epigenetics](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-3/epigenetics-2/)
- [Polymerase chain reaction (PCR)](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-4/polymerase-chain-reaction-pcr/)
- [DNA probes, microarrays and genetic fingerprinting](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-4/dna-probes-microarrays-and-genetic-fingerprinting/)
- [Gene cloning](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-4/gene-cloning/)
- [Transgenic animals and plants](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-4/transgenic-animals-and-plants/)
- [Gene therapy](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-4/gene-therapy/)
- [Genome sequencing](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-4/genome-sequencing/)
- [Ethics and safety of gene technology](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-4/ethics-and-safety-of-gene-technology/)
- [Inheritance](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-5/inheritance-2/)
- [Genetic interactions and properties](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-5/genetic-interactions-and-properties/)
- [Gene pools](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-6/gene-pools/)
- [Hardy-Weinberg principle](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-6/hardy-weinberg-principle/)
- [Causes of variation](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-6/causes-of-variation/)
- [Selection](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-6/selection/)
- [Speciation](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-6/speciation/)
- [Bryophyta (e.g. moss) form and adaptations](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-7/bryophyta-e-g-moss-form-and-adaptations/)
- [Tracheophyta (e.g. fern) form](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-7/tracheophyta-e-g-fern-form/)
- [Angiosperm (e.g. flowering plant) form and adaptations](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-7/angiosperm-e-g-flowering-plant-form-and-adaptations/)
- [Cnidaria (e.g. Hydra) body form](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-8/cnidaria-e-g-hydra-body-form/)
- [Platyhelminthes (e.g. flatworm) body form](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-8/platyhelminthes-e-g-flatworm-body-form/)
- [Annelida (e.g. earthworm) body form](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-8/annelida-e-g-earthworm-body-form/)
- [Arthropoda (e.g. insect) body form](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-8/arthropoda-e-g-insect-body-form/)
- [Chordata (e.g. cat) body form](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-8/chordata-e-g-cat-body-form/)
- [Surface area to volume ratio](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-1/surface-area-to-volume-ratio/)
- [Mass transport](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-1/mass-transport/)
- [Gas Exchange](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-1/gas-exchange-2/)
- [Transport in plants](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-1/transport-in-plants/)
- [Mammalian circulation](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-1/mammalian-circulation-2/)
- [Mammalian heart](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-1/mammalian-heart/)
- [Blood and tissue fluid](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-1/blood-and-tissue-fluid/)
- [Blood clotting](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-1/blood-clotting/)
- [Haemoglobin](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-1/haemoglobin-2/)
- [Population distribution](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-2/population-distribution/)
- [Diversity Amongst Organisms](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-3/diversity-amongst-organisms/)
- [Measuring Diversity](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-3/measuring-diversity/)
- [Taxonomy](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-3/taxonomy/)
- [The Five Kingdoms](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-3/the-five-kingdoms/)
- [Human environmental impact](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-3/human-environmental-impact/)
- [Supporting biodiversity](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-3/supporting-biodiversity/)
- [Introduction to cells](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-1/introduction-to-cells/)
- [Ultrastructure of cells](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-1/ultrastructure-of-cells/)
- [Membrane structure](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-1/membrane-structure/)
- [Membrane transport](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-1/membrane-transport/)
- [The origin of cells](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-1/the-origin-of-cells/)
- [Cell division](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-1/cell-division/)
- [Water](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-2/water-5/)
- [Carbohydrates and lipids](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-2/carbohydrates-and-lipids/)
- [Proteins](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-2/proteins-5/)
- [Enzymes](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-2/enzymes-3/)
- [Structure of DNA and RNA](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-2/structure-of-dna-and-rna-2/)
- [DNA replication, transcription and translation](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-2/dna-replication-transcription-and-translation/)
- [Cell respiration](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-2/cell-respiration-3/)
- [Photosynthesis](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-2/photosynthesis-6/)
- [Genes](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-3/genes/)
- [Chromosomes](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-3/chromosomes-2/)
- [Meiosis](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-3/meiosis-5/)
- [Inheritance](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-3/inheritance-4/)
- [Genetic modification and biotechnology](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-3/genetic-modification-and-biotechnology/)
- [Species, communities and ecosystems](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-4/species-communities-and-ecosystems/)
- [Energy flow](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-4/energy-flow-2/)
- [Climate change](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-4/climate-change/)
- [Evidence for evolution](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-5/evidence-for-evolution/)
- [Natural selection](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-5/natural-selection-3/)
- [Classification of biodiversity](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-5/classification-of-biodiversity/)
- [Cladistics](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-5/cladistics/)
- [Digestion and absorption](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-6/digestion-and-absorption-2/)
- [The blood system](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-6/the-blood-system/)
- [Defence against infectious disease](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-6/defence-against-infectious-disease/)
- [Gas exchange](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-6/gas-exchange-4/)
- [Hormones, homeostasis and reproduction](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-6/hormones-homeostasis-and-reproduction/)
- [DNA structure and replication](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-1/dna-structure-and-replication/)
- [Transcription and gene expression](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-1/transcription-and-gene-expression/)
- [Translation](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-1/translation/)
- [Metabolism](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-2/metabolism/)
- [Photosynthesis](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-2/photosynthesis-5/)
- [Transport in the xylem of plants](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-3/transport-in-the-xylem-of-plants/)
- [Transport in the phloem of plants](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-3/transport-in-the-phloem-of-plants/)
- [Growth in plants](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-3/growth-in-plants/)
- [Reproduction in plants](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-3/reproduction-in-plants/)
- [Meiosis](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-4/meiosis-4/)
- [Inheritance](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-4/inheritance-3/)
- [Gene pools and speciation](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-4/gene-pools-and-speciation/)
- [Antibody production and vaccination](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-5/antibody-production-and-vaccination/)
- [Movement](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-5/movement/)
- [The kidney and osmoregulation](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-5/the-kidney-and-osmoregulation/)
- [Sexual reproduction](https://thealevelbiologist.co.uk/exam-boards/ib-ahl/module-5/sexual-reproduction/)
- [(Core) Neural development](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-1/neural-development/)
- [(Core) The human brain](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-1/the-human-brain/)
- [(Core) Perception of stimuli](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-1/perception-of-stimuli/)
- [(AHL) Innate and learned behaviour](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-1/innate-and-learned-behaviour/)
- [(AHL) Neuropharmacology](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-1/neuropharmacology/)
- [(AHL) Ethology](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-1/ethology/)
- [(Core) Microbiology: organisms in industry](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-2/microbiology-organisms-in-industry/)
- [(Core) Biotechnology in agriculture](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-2/biotechnology-in-agriculture/)
- [(Core) Environmental protection](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-2/environmental-protection/)
- [(AHL) Medicine](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-2/medicine/)
- [(AHL) Bioinformatics](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-2/bioinformatics/)
- [(Core) Species and communities](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-3/species-and-communities/)
- [(Core) Communities and ecosystems](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-3/communities-and-ecosystems-2/)
- [(Core) Impacts of humans on ecosystems](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-3/impacts-of-humans-on-ecosystems/)
- [(AHL) Population ecology](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-3/population-ecology/)
- [(Core) Human nutrition](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-4/human-nutrition/)
- [(Core) Digestion](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-4/digestion/)
- [(Core) Functions of the liver](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-4/functions-of-the-liver/)
- [(Core) The heart](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-4/the-heart/)
- [(AHL) Hormones and metabolism](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-4/hormones-and-metabolism/)
- [(AHL) Transport of respiratory gases](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-4/transport-of-respiratory-gases/)
- [Cell structure and organisation](https://thealevelbiologist.co.uk/exam-boards/sat/module-1/cell-structure-and-organisation/)
- [Mitosis](https://thealevelbiologist.co.uk/exam-boards/sat/module-1/mitosis-3/)
- [Enzymes](https://thealevelbiologist.co.uk/exam-boards/sat/module-1/enzymes-2/)
- [Biosynthesis](https://thealevelbiologist.co.uk/exam-boards/sat/module-1/biosynthesis/)
- [Energy flow](https://thealevelbiologist.co.uk/exam-boards/sat/module-2/energy-flow/)
- [Nutrient cycles](https://thealevelbiologist.co.uk/exam-boards/sat/module-2/nutrient-cycles-3/)
- [Populations](https://thealevelbiologist.co.uk/exam-boards/sat/module-2/populations-2/)
- [Communities](https://thealevelbiologist.co.uk/exam-boards/sat/module-2/communities/)
- [Biomes](https://thealevelbiologist.co.uk/exam-boards/sat/module-2/biomes/)
- [Conservation biology](https://thealevelbiologist.co.uk/exam-boards/sat/module-2/conservation-biology/)
- [Biodiversity](https://thealevelbiologist.co.uk/exam-boards/sat/module-2/biodiversity-3/)
- [Effects of human intervention](https://thealevelbiologist.co.uk/exam-boards/sat/module-2/effects-of-human-intervention/)
- [Meiosis](https://thealevelbiologist.co.uk/exam-boards/sat/module-3/meiosis-3/)
- [Mendelian genetics](https://thealevelbiologist.co.uk/exam-boards/sat/module-3/mendelian-genetics/)
- [Inheritance patterns](https://thealevelbiologist.co.uk/exam-boards/sat/module-3/inheritance-patterns/)
- [Molecular genetics](https://thealevelbiologist.co.uk/exam-boards/sat/module-3/molecular-genetics/)
- [Population genetics](https://thealevelbiologist.co.uk/exam-boards/sat/module-3/population-genetics/)
- [Plant structure and function](https://thealevelbiologist.co.uk/exam-boards/sat/module-4/plant-structure-and-function/)
- [Animal structure and function](https://thealevelbiologist.co.uk/exam-boards/sat/module-4/animal-structure-and-function/)
- [Animal behaviour](https://thealevelbiologist.co.uk/exam-boards/sat/module-4/animal-behaviour/)
- [Origin of life](https://thealevelbiologist.co.uk/exam-boards/sat/module-5/origin-of-life/)
- [Evidence of evolution](https://thealevelbiologist.co.uk/exam-boards/sat/module-5/evidence-of-evolution/)
- [Patterns of evolution](https://thealevelbiologist.co.uk/exam-boards/sat/module-5/patterns-of-evolution/)
- [Natural selection](https://thealevelbiologist.co.uk/exam-boards/sat/module-5/natural-selection-2/)
- [Speciation](https://thealevelbiologist.co.uk/exam-boards/sat/module-5/speciation-2/)
- [Classification and diversity of organisms](https://thealevelbiologist.co.uk/exam-boards/sat/module-5/classification-and-diversity-of-organisms/)
- [Enzymes](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-1/enzymes/)
- [Investigating diversity](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-4/investigating-diversity/)
- [Biodiversity within a community](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-4/biodiversity-within-a-community/)
- [Species and taxonomy](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-4/species-and-taxonomy/)
- [Genetic diversity and adaptation](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-4/genetic-diversity-and-adaptation/)
- [Genetic diversity can arise as a result of mutation or during meiosis](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-4/genetic-diversity-can-arise-as-a-result-of-mutation-or-during-meiosis/)
- [DNA and protein synthesis](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-4/dna-and-protein-synthesis/)
- [DNA, genes and chromosomes](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-4/dna-genes-and-chromosomes/)
- [Mass transport in plants](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-3/mass-transport-in-plants/)
- [Digestion and absorption](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-3/digestion-and-absorption/)
- [Gas exchange](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-3/gas-exchange/)
- [Size and Surface Area](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-3/size-and-surface-area/)
- [Cell recognition and the immune system](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-2/cell-recognition-and-the-immune-system/)
- [Transport across cell membranes](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-2/transport-across-cell-membranes/)
- [All cells arise from other cells](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-2/all-cells-arise-from-other-cells/)
- [Methods of studying cells](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-2/methods-of-studying-cells/)
- [Structure of Prokaryotic Cells and of Viruses](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-2/structure-of-prokaryotic-cells-and-of-viruses/)
- [Inorganic Ions](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-1/inorganic-ions/)
- [Water](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-1/water/)
- [Replication of DNA](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-1/replication-of-dna/)
- [Structure of DNA and RNA](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-1/structure-of-dna-and-rna/)
- [Many proteins are enzymes](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-1/many-proteins-are-enzymes/)
- [Proteins](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-1/proteins/)
- [Lipids](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-1/lipids/)
- [Carbohydrates](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-1/carbohydrates/)
- [Monomers and Polymers](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-1/monomers-and-polymers/)
- [❤️ Biological chemistry](https://thealevelbiologist.co.uk/exam-boards/sat/module-1/biological-chemistry/)
- [☝️ Neurons and synapses](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-6/neurons-and-synapses/)
- [♻️ Carbon cycling](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-4/carbon-cycling/)
- [☀️ Photosynthesis](https://thealevelbiologist.co.uk/exam-boards/sat/module-1/photosynthesis-4/)
- [⚡ Nerve Impulses](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-2/nerve-impulses/)
- [✋ Principles of homeostasis and negative feedback](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-2/principles-of-homeostasis-and-negative-feedback/)
- [❤️ Mass transport in animals](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-3/mass-transport-in-animals/)
- [⚡ Nerve impulses and the motor neurone](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-8/nerve-impulses-and-the-motor-neurone/)
- [⚙️ Link reaction and Krebs cycle](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-1/link-reaction-and-krebs-cycle/)
- [⚡ Glycolysis](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-1/glycolysis/)
- [⚙️ Eukaryotic and prokaryotic cell structure and function](https://thealevelbiologist.co.uk/exam-boards/edexcel-as/module-2/eukaryotic-and-prokaryotic-cell-structure-and-function/)
- [⚙️ Molecules to metabolism](https://thealevelbiologist.co.uk/exam-boards/ib-core/module-2/molecules-to-metabolism/)
- [⚖️ Control of blood water potential](https://thealevelbiologist.co.uk/exam-boards/aqa-a2/module-2/control-of-blood-water-potential/)
- [⛓️ Synapse](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-8/synapse/)
- [(AHL) ⚡ Nitrogen and phosphorus cycles](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-3/nitrogen-and-phosphorus-cycles/)
- [(Core) ⛰️ Conservation of biodiversity](https://thealevelbiologist.co.uk/exam-boards/ib-options/module-3/conservation-of-biodiversity/)
- [⛰️ Ecosystems](https://thealevelbiologist.co.uk/exam-boards/sat/module-2/ecosystems-2/)
- [☀️ Mutagens, carcinogens and oncogenes](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-3/mutagens-carcinogens-and-oncogenes/)
- [⚖️ Homeostasis and negative feedback](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-7/homeostasis-and-negative-feedback/)
- [⚱️ Species Extinction](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-6/species-extinction/)
- [⚠️ Planetary boundaries](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-6/planetary-boundaries/)
- [☘️ Photosynthesis](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-2/photosynthesis-2/)
- [⚙️ Aerobic respiration and photosynthesis: ATP production](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-3/module-1/aerobic-respiration-and-photosynthesis-atp-production/)
- [♂️ Sex linkage in haemophilia and Duchenne muscular dystrophy](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-3/sex-linkage-in-haemophilia-and-duchenne-muscular-dystrophy/)
- [⚽ Ovary, testis, oogenesis and spermatogenesis](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-unit-4/module-1/ovary-testis-oogenesis-and-spermatogenesis/)
- [⚖️ Sympathetic and parasympathetic nervous systems](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-3/sympathetic-and-parasympathetic-nervous-systems/)
- [⚙️ Structure of cartilage](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-2/structure-of-cartilage/)
- [⚠️ Pathogens](https://thealevelbiologist.co.uk/exam-boards/wjec-a2-options/module-1/pathogens/)
- [⛓️ Synapse](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-3/synapse-2/)
- [☀️ Energy transfer](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-1/module-4/energy-transfer/)
- [⚡ ATP](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-1/atp-3/)
- [♀️♂️ Sex determination and sex linkage](https://thealevelbiologist.co.uk/exam-boards/ccea-a2-unit-2/module-5/sex-determination-and-sex-linkage/)
- [⚙️ Cell Cycle](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-1/module-6/cell-cycle-2/)
- [☔ Adaptation to the environment](https://thealevelbiologist.co.uk/exam-boards/ccea-as-unit-2/module-2/adaptation-to-the-environment/)
- [⚖️ Osmoregulation and temperature regulation](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-5/osmoregulation-and-temperature-regulation/)
- [✋ Antibiotic Resistance](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-2/antibiotic-resistance/)
- [⚠️ Other pathogenic agents](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-2/other-pathogenic-agents/)
- [☀️ Photosynthesis](https://thealevelbiologist.co.uk/exam-boards/edexcel-a2/module-1/photosynthesis-3/)
- [⚖️ The principles and importance of homeostasis](https://thealevelbiologist.co.uk/exam-boards/ocr-a2/module-2/the-principles-and-importance-of-homeostasis/)
- [☀️ Mutations](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-1/mutations/)
- [⛰️ Field techniques for biologists](https://thealevelbiologist.co.uk/exam-boards/scottish-advanced-higher/module-2/field-techniques-for-biologists/)
- [⛅ Food supply, plant growth and productivity](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-3/food-supply-plant-growth-and-productivity/)
- [⚠️ Ethical considerations in the use of microorganisms — hazards and control of risks](https://thealevelbiologist.co.uk/exam-boards/scottish-higher/module-2/ethical-considerations-in-the-use-of-microorganisms-hazards-and-control-of-risks/)
- [⚙️ Structure of eukaryotic cells](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-2/structure-of-eukaryotic-cells/)
- [☕ ATP](https://thealevelbiologist.co.uk/exam-boards/aqa-as/module-1/atp/)

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