Light-independent reactions and the Calvin cycleEdexcel International A Level Biology: Mind map

Exam questions on Light-independent reactions and the Calvin cycle

1. A student isolates intact chloroplasts from spinach leaves and suspends them in a buffer containing hydrogencarbonate ions, which act as a source of carbon dioxide. In the light, the chloroplasts take up carbon dioxide and make GALP.
   Explain why isolated chloroplasts kept in the dark in this buffer cannot make GALP, even though carbon dioxide is available.2 marks
2. A plant biochemist is calculating the energy requirements of the Calvin cycle in a leaf. She assumes that, for every carbon dioxide molecule fixed, the cycle uses 3 molecules of ATP and 2 molecules of reduced NADP.
   Explain why most of the GALP made in the Calvin cycle is not used to make carbohydrate but is used in another process.2 marks
3. Tomato plants grown in a glasshouse are supplied with carbon dioxide containing radioactive ¹⁴C for a short time. Later, radioactivity is found in the starch in the leaves, the cellulose in the cell walls, the proteins in the fruits and the lipids in the seeds.
   Describe how carbon from carbon dioxide is incorporated into GALP in the Calvin cycle.3 marks