Naked Science Forum
Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: paul.fr on 10/07/2007 07:38:46
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if Chlorophyll gives plants their green colour, why are some plants/leaaves more or less green than others? Do they take in more/less chlorophyll, is it pigments or what?
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Here's some text I wrote from the "pink trees" thread:
Chlorophyll absorbs light and provides the energy for photosynthesis. The wavelength in which chlorophyll works best is in the red and blue range, and therefore does not absorb the green wavelength which is why leaves appear green. There are 2 chlorophylls at work - "a" and "b". They both operate in a slightly different frequency, thus increasing the total energy use from the sun. Chlorophyll "a" operates in the 400-450 & 650-700 nm frequencies (purple and red) while "b" operates in the 450-500 & 600-650 nm frequencies (blue and orange). They also generally exist in a 3 to 1 ratio, a to b. The gap left (500 - 600 nm) is the green zone. In some tree's leaves, the chlorophyll "a" is less dominant, therefore there is an increase in the anount of purple and red wavelengths reflected, hence the leaves are more purpley in colour, while the tree is still able to photosynthesize.
Here's the new bit....
It's a mixture of these that provides the different colouration. The reason that not all plants are the same colour is the fact that if they were, they would all be in competition for the same energy resource, ie, that wavelength of light. Plants have become adapted to these slightly different wavelengths in order to use the energy that is not being used by others. It's in some ways comparable to birds using different parts of the same tree - there would be no point in them all using the same part, and so they have adapted to a niche resource.
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There are also other pigments found in plants, that contribute to the colour of the leaves.... Carotenoids of various types being the main accessory pigments.
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There are also other pigments found in plants, that contribute to the colour of the leaves.... Carotenoids of various types being the main accessory pigments.
This is true, but are only generally visible once the chlorophyll is dispated, hence the Autumn colours.
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Only visible on their own, but they still make a difference to the overall shade of the leaf! (and look at the colour of a copper beech... it still has chlorophyll)
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The reds and purples of some species are formed by the leaves having high levels of anthocyanin pigments which combine with the chlorophyll pigment to produce the colours. There are other accessory pigments too. Carotenoids is an example (I'm not denying it!), but Copper beech has anthocyanin pigment. But, my understanding is that although carotenoids aid with energy absorbtion, their pigment is not the one visible on reddish leaved trees, and isn't visible until the chlorophyll has been dissipated. It's the anthocyanin that is the key accessory pigment in this instance.
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Just because it isn't the dominant pigment, doesn't mean it doesn't contribute to the overall colour. If you do a pigment extraction of different plants, all the pigments will contribute to the spectrum you get. If chlorophyll were the only pigment (and chlorophyll A and B are pretty well indistinguishable to our eyes), all leaves would be the same colour, which they're not.