Cellular Respiration



Aerobic Respiration

Glycolysis Lipid and Protein Substrates

Anaerobic Respiration 

Yeast Fermentation and the production of Ethanol

The Citric Acid (krebs) Cycle

Oxidative Phosphorylation

The Respiratory Quotient 

RQ=CO₂ eliminated / O₂ consumed





Respiration is the cellular energy-yielding process that occurs across the life domains (bacteria, archaea, eukaryota).

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.


Its overall reaction is:
glucose + oxygen –> carbon dioxide + water + heat energy

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 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 our cells produce energy (ATP).


Anaerobic respiration occurs in the absence of oxygen, unlike aerobic respiration. Some organisms such as certain types of bacteria carry out anaerobic respiration as the main or only kind of respiration, while other organisms such as ourselves only carry out anaerobic respiration under special circumstances……

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