This is a legacy topic. View the most up to date content by selecting the exam board in the dropdown to the left.
The example for this topic will be (as per the specification) a palisade cell from a leaf. This is where palisade cells are located within 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:
Look at the black and white image. That is a micrograph of a leaf showing palisade cells along the surface. The blob in the centre that looks like a face is a palisade cell. The spheres lining its perimetre are chloroplasts. Can you spot the nucleus? Each palisade cell is surrounded by its cell wall which is made of cellulose.
The role of the cell wall is multi-fold:
1. Provides the plant with strength
2. Prevents the cell from bursting due to water flooding in by exerting pressure against the water flow
3. Gives tissues mechanical strength e.g. plants that rise high above the ground
4. Maintains the cell’s specific shape.
Just a quick break here. Why are we looking at palisade cells? Well. palisade cells are the ones containing copious amounts of chloroplasts. And chloroplasts contain all the substances and machinery necessary for photosynthesis. Without photosynthesis, you and I would not be here right now. Impressive. Take a closer look at this intricate organelle, the chloroplast, to whom we owe our lives:
This gooey mess whose constituent components have slightly uncommon and incredibly hard to memorise names is a chloroplast. Let’s crunch them one by one.
Thylakoid, a disc-shaped organelle which contains chlorophyll (the lovely green pigment) rhymes with Kayla+Droid. Trust me, once you get the hang of this little word you will love it. Chlorophyll is involved in capturing sunlight (and the light dependent reaction). Multiple thylakoids stack together like towers within the chloroplast. A tower is called a granum, pl. grana. This arrangement enhances the surface area available.
The stroma is the fluid-filled space which is the site of the light-independent reaction.
The outer membrane and inner membrane are selectively permeable to allow O2, CO2, glucose and certain ions through.
Features which make chloroplasts well adapted to serve their function:
1. Chloroplasts are relatively flat and so ease the diffusion of molecules coming in and going out. This is achieved by a shorter diffusion pathway.
2. Plenty of available surface area for the reaction between chlorophyll and light to take place.
Now that wasn’t so bad!