CAIE A Level Biology 9700 · Photosynthesis
The table shows the percentage absorption of light at different wavelengths by chlorophyll a and chlorophyll b extracted from a plant.
| Wavelength (nm) | Chlorophyll a (% absorption) | Chlorophyll b (% absorption) |
|---|---|---|
| 430 | 80 | 55 |
| 450 | 65 | 75 |
| 500 | 20 | 30 |
| 550 | 10 | 40 |
| 600 | 40 | 30 |
| 650 | 70 | 80 |
| 680 | 75 | 60 |
| 700 | 50 | 20 |
Explain why plants contain both chlorophyll a and chlorophyll b, and how the light-dependent stage provides the products needed for the Calvin cycle.
6 marks, so the mark scheme is looking for about 6 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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