3.2.4 The variety of life is extensive and this is reflected in similarities and differences in its biochemical basis and cellular organisation.
There are fundamental differences between plant cells and animal cells.
The structure of a palisade cell from a leaf as seen with an optical microscope. The appearance, ultrastructure and function of cell wall and chloroplasts. Candidates should be able to apply their knowledge of these and other eukaryotic features in explaining adaptations of other plant cells.
Plants 🌿 and animals 🐶differ both macroscopically and in terms of the individual cells that make them up. In GCE AQA Biology, you should be able to remember these cellular differences summarised in the following table:
There are individual organelles particular to plant cells that are very interesting 🌵. As a student of GCE AQA Biology, you will be expected to know the appearance, ultrastructure and function of the cell wall and chloroplasts.
- Mostly made up of microfibrils (small bundles) of cellulose
- Microfibrils are embedded and intertwined with a matrix
- Contains some other polysaccharides
- Surrounded by a thin layer (middle lamella) that joins up neighbouring cells
- Prevent the cell from bursting due to excessive water entry - the cellulose microfibrils are very strong
- Support and provide the plant with strength
- Allow water to pass along it
- Surrounded by a double plasma membrane called the chloroplast envelope
- Chlorophyll is contained in thylakoids, each of which is a disc-like structure
- Thylakoids are arranged in stacks called grana (the singular form is granum)
- Grana are joined up by lamella
- The grana/lamella are held inside the chloroplast. The interior space is known as the stroma, which contains a matrix holding starch grains and enzymes for the Calvin cycle
Chloroplasts are meant to absorb sunlight and use it to carry out photosynthesis. The chloroplast is adapted to do so:
- The stacked thylakoids create a large surface area to volume ratio that increases the rate of the light-dependent reactions
- The stroma contains enzymes for making glucose in the Calvin cycle
- Chloroplasts have their own DNA and ribosomes that allow fast protein synthesis for photosynthesis
The following diagram summarises the organelles in a plant cell, specifically a palisade leaf cell:
Plant cells are adapted to their specific functions ☘️. For example, a palisade leaf cell will have lots of chloroplasts, as the leaves are exposed to sunlight and can thus photosynthesise, whereas a root cell will not have chloroplasts, as the roots are deep underground, away from sunlight, and thus will not photosynthesise.
That's it for this section!
Toole, G., & Toole, S. (2015). Aqa biology A level. Oxford: Oxford University Press.