Nicholas Lealand, of Cashmere High School, asks :-
I have seen several different colours of lichen (yellow, white, orange) which have no green, so they cannot have chlorophyll in them. If so, how do they photosynthesise?
Paul Broady, a Botanist at the University of Canterbury, responded.
There is a big assumption in this question. This is that a plant which does not look green cannot contain chlorophyll. Have a look at the trees, shrubs and herbaceous plants in local gardens and parks. Are they all green? No, some are varieties which have purplish-red leaves. They must photosynthesise as in every other respect they are just like typical green plants. They grow with the aid of sunlight, carbon dioxide, water and mineral salts, just like all lichens.
How can we investigate these more closely? Well the easiest way is to break off a small fragment of the leaf or lichen and examine it under a light microscope. You will see the cells which make up the plant and in some of these you will see green structures. These are called chloroplasts and contain the green pigment chlorophyll. In the purplish leaves and the lichens the chlorophyll is there but the green colour is masked by large amounts of other coloured chemicals. You can see the same effect if you look at a green card through bright red coloured plastic sheet. The card no longer looks green but you know it is still there!
Some of these other chemicals are produced by plants in order to protect the chloroplasts from the damaging effect of intense sunlight and ultra-violet radiation. They are just like sunscreens. Another way you could investigate these odd-coloured plants is by using a technique called chromatography. See if you can find out more about this technique. May be you could you use it in the classroom to separate the different coloured pigments in different plants?