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AQA A-level Biology — Energy Transfers flashcards

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AQA A-level Biology topic 5: the light-dependent and light-independent reactions, glycolysis to oxidative phosphorylation, required practicals 7–9, primary and secondary production, and the nitrogen and phosphorus cycles.

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Learn deck · part of AQA A-level Biology · written against: AQA AS and A-level Biology (7401/7402) specification, version 1.6, July 2026 (eight topics). Updated 2026-10-10.

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  1. What is photoionisation of chlorophyll?
    Light energy excites electrons in chlorophyll to a higher energy level so that they leave the chlorophyll molecule.

    The chlorophyll is left positively charged (ionised) until its electrons are replaced.
    Energy Transfers › Photosynthesis
  2. In the light-dependent reaction, which two products conserve some of the energy of the excited electrons?
    ATP and reduced NADP.

    Both are then used in the light-independent reaction.
    Energy Transfers › Photosynthesis
  3. How does the electron transfer chain in a chloroplast lead to a proton gradient?
    Electrons pass along carriers in the thylakoid membrane in redox reactions, releasing energy that pumps protons into the thylakoid space.

    Protons also build up there from photolysis of water.
    Energy Transfers › Photosynthesis
  4. How do protons make ATP in a chloroplast, according to the chemiosmotic theory?
    Protons diffuse down their electrochemical gradient from the thylakoid space into the stroma through ATP synthase, which joins ADP and Pi.

    Mitochondria make ATP by the same mechanism across their inner membrane.
    Energy Transfers › Photosynthesis
  5. What are the products of photolysis of water?
    Protons, electrons and oxygen (2H₂O → 4H⁺ + 4e⁻ + O₂).

    The electrons replace those lost from chlorophyll by photoionisation; the oxygen is a by-product.
    Energy Transfers › Photosynthesis
  6. What is the final acceptor of electrons in the light-dependent reaction?
    NADP, which is reduced to reduced NADP.

    It accepts the electrons together with protons at the end of the electron transfer chain.
    Energy Transfers › Photosynthesis
  7. In the light-independent reaction, what happens to carbon dioxide first, and which enzyme catalyses it?
    It combines with ribulose bisphosphate (RuBP), and the six-carbon product splits at once into two molecules of glycerate 3-phosphate (GP); rubisco catalyses the step.

    This fixes inorganic carbon into an organic molecule.
    Energy Transfers › Photosynthesis
  8. How is GP converted to triose phosphate?
    GP is reduced using reduced NADP, with energy from ATP hydrolysis, both from the light-dependent reaction.

    Reduced NADP supplies the hydrogen; ATP supplies the energy.
    Energy Transfers › Photosynthesis
  9. What happens to the triose phosphate made in the Calvin cycle?
    Most is used to regenerate RuBP, using ATP; the rest is made into other organic compounds the plant needs, such as glucose, amino acids and lipids.

    Regenerating RuBP keeps the cycle going.
    Energy Transfers › Photosynthesis
  10. A plant in bright light is suddenly put in the dark. What happens to the amounts of GP and RuBP, and why?
    GP rises and RuBP falls: without ATP and reduced NADP, GP is not reduced and RuBP is not regenerated, but RuBP still combines with CO₂ for a while.

    This kind of data shows the order of steps in the Calvin cycle.
    Energy Transfers › Photosynthesis

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About these cards

Review status: Second-reader reviewed, with corrections applied.

Checked against:

  • Topic outline follows the AQA AS and A-level Biology (7401/7402) specification, version 1.6 (July 2026) (outline only; no specification text reproduced).
  • OpenStax Biology 2e, consulted as a reference; no text copied.
  • Also checked against the AQA AS and A-level Biology required practical handbook, version 2.3 (January 2026) (reference only; no text copied).

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