A student plots the absorption spectrum of pure chlorophyll a and the action spectrum of a leaf on…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student plots the absorption spectrum of pure chlorophyll a and the action spectrum of a leaf on one graph. Both curves have a peak in the blue and one in the red. But in the blue-green region, near , the action spectrum is clearly higher than the chlorophyll a curve. (a) What does this tell you? (b) Name the pigments that fill the gap. (c) What do these pigments do with the light they absorb? (d) Give one more job that they do.
Need a reminder? The key ideaShow
Pigments: chlorophyll a (bright or blue green), chlorophyll b (yellow green), xanthophylls (yellow), carotenoids (yellow to yellow-orange). . Chlorophyll a absorbs best in blue and red. The action spectrum follows the absorption spectrum but is higher where accessory pigments add their light, and accessory pigments also protect chlorophyll a from photo-oxidation.
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The meaning. Chlorophyll a is not the only pigment that supplies light for photosynthesis. Other pigments absorb near .
Step 2. The helpers. The accessory pigments: chlorophyll b, xanthophylls and carotenoids.
Step 3. Their light. They pass the energy they absorb on to chlorophyll a, which takes part in the reactions that follow.
Step 4. The extra job. They protect chlorophyll a from photo-oxidation.
Answer: (a) other pigments also supply light energy; (b) chlorophyll b, xanthophylls, carotenoids; (c) they pass the energy to chlorophyll a; (d) they protect chlorophyll a from photo-oxidation.
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