Here is a diagram of a plant palisade mesophyll cell:
I have underlined the labels you need to know about in green.
You might get asked how this cell is specialised for its function. Well, this kind of cell is found in a leaf and it has many chloroplasts for photosynthesis.
Chloroplasts contain photosynthetic pigments. You have probably heard of “chlorophyll” which is needed for photosynthesis. If there was only one kind of photosynthetic pigment you would expect all green plants to be exactly the same shade of green, but they are not. This is because there are several different photosynthetic pigments and different plants have different amounts of each one and they are not all the same colour.
- Chlorophyll a
- Chlorophyll b
- Chlorophyll c
They are all slightly different colours. You do not need to worry about this for your GCSE exam, but you will need to know about this when you start your “A” Level biology course. It is possible to separate these pigments from leaves using a technique called “chromatography”. Thin Layer Chromatography (TLC) is an excellent way of proving that there is more than one kind of chlorophyll. The colours you will see are blue-green, green, yellow-green, yellow, orange and even grey. The grey pigment is actually a breakdown product from chlorophyll.
Plants can use light energy to convert carbon dioxide and water into glucose and oxygen. To do this they must have chlorophyll. Photosynthesis takes place in the green parts of plant; we call these the leaves !!!!! You know that there is no chlorophyll in the cells in the roots because you know that roots are NOT green. Anyway, roots are usually underground and therefore in the dark so photosynthesis would not be possible even if the root cells did contain chlorophyll.
All of the last paragraph was totally obvious: so it should be obvious that the following diagram shows a plant cell even though it does not contain chloroplasts. Here is a “root hair” cell:
Osmosis and turgidity
Osmosis is very important in root hair cells. Providing that the soil is moist, it is possible for water to enter the root hair by osmosis. (See my Osmosis Page if you have forgotten about this.) Water passes from a region of high water concentration (wet soil) through a semi-permeable membrane (the cell membrane) to a region of lower water concentration (the cytoplasm). This makes the cell turgid. As these cells develop they absorb water by osmosis and the hair can be pushed between soil particles.
The most important thing to remember about root hairs is that they increase the surface area between the root and the soil: this is necessary for the absorption of water and mineral salts.
Examiners like to ask you what is special about this cell. They put a diagram like this in the exam paper (perhaps without the labels) and then ask “How is this cell specialized or adapted for its function?” You will write down “It has a large surface area to speed up the absorption of water and mineral salts from the soil.” Poor old examiner will have to give you a mark. Actually examiners like to give you marks, but only if you know the right answer.