The Calvin cycleEdexcel A-Level Biology A: Flashcards

Exam questions on The Calvin cycle

1. In the 1950s Melvin Calvin and his team supplied the green alga Chlorella with carbon dioxide containing radioactive carbon-14, in bright light. After a measured time, samples of the algae were dropped into hot ethanol. The compounds in each sample were separated by chromatography and the radioactive ones were identified. After 5 seconds nearly all the radioactivity was in one compound, but after 30 seconds it was found in many compounds.
   Suggest why, after 30 seconds, the radioactive carbon was found in many different compounds.2 marks
2. A suspension of Chlorella is kept in bright light with a constant supply of carbon dioxide, and the concentrations of GP and RuBP inside the cells stay steady. The light is then switched off, while the carbon dioxide supply continues unchanged, and the concentrations of GP and RuBP are measured over the next minute.
   Explain the changes in the concentrations of GP and RuBP after the light is switched off.2 marks
3. A tomato grower raises the carbon dioxide concentration in a greenhouse from 0.04% to 0.1%, in bright light at 25 °C. In the Calvin cycle in the leaf cells, each molecule of GP is reduced to one molecule of GALP using one molecule of ATP and one molecule of reduced NADP, and the regeneration of each molecule of RuBP from GALP uses one molecule of ATP.
   Explain how the increase in carbon dioxide concentration affects the concentrations of GP and RuBP in the leaf cells, and why the rate of carbon fixation does not keep on increasing as carbon dioxide is added.3 marks