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The light-independent stage and limiting factorsEdexcel A-Level Biology B: Flashcards

What these 13 flashcards ask

  • Where does the light-independent stage take place?
  • What is carbon fixation?
  • What is RuBP?
  • What does RUBISCO stand for and do?
  • What happens to the six-carbon compound formed in fixation?
  • What is GP?
  • How is GP converted to GALP?
  • What happens to most of the GALP?
  • Name three uses of the GALP that leaves the cycle.
  • What happens to GP and RuBP when light is switched off?
  • Name three factors that limit photosynthesis.
  • Why does the rate fall at high temperature?
  • What happens to the rate when a different factor becomes limiting?

Exam questions on The light-independent stage and limiting factors

  1. Cells of the green alga Chlorella were kept in bright light with a constant supply of carbon dioxide, so that the Calvin cycle was running steadily. The light was then switched off while the carbon dioxide supply continued, and the concentrations of ribulose bisphosphate (RuBP) and glycerate 3-phosphate (GP) in the cells were measured.
    Explain the changes in the concentrations of GP and RuBP after the light was switched off.2 marks
  2. A grower produces tomatoes in a glasshouse. In winter she adds carbon dioxide to the air, uses artificial lighting and heats the glasshouse, but keeps the temperature below 35 °C.
    The grower finds that raising the temperature from 15 °C to 25 °C increases the rate of photosynthesis when light and carbon dioxide are plentiful. Explain why.2 marks
  3. A leaf was illuminated at a constant light intensity and a constant temperature of 25 °C. The rate of photosynthesis was 8 arbitrary units at 0.04% carbon dioxide, 14 arbitrary units at 0.08% and 15 arbitrary units at 0.12%.
    Calculate the percentage increase in the rate of photosynthesis when the carbon dioxide concentration is raised from 0.04% to 0.08%.3 marks
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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).