Light-dependent reactionsEdexcel International A Level Biology: Mind map

Exam questions on Light-dependent reactions

1. The light-dependent reactions of photosynthesis take place in the thylakoid membranes of chloroplasts, where molecules of chlorophyll are arranged in groups called photosystems.
   Describe how the energy of excited electrons is used to make ATP.2 marks
2. In non-cyclic photophosphorylation, electrons that leave chlorophyll in photosystem II are replaced by electrons that come from water. Isolated chloroplasts that are illuminated in a suspension release oxygen.
   Explain why photosystem II needs electrons from water for non-cyclic photophosphorylation to continue.2 marks
3. DCMU is a chemical that blocks the movement of electrons from photosystem II to the electron transport chain. Far-red light, with a wavelength greater than 700 nm, is absorbed only by photosystem I. A researcher illuminated suspensions of isolated chloroplasts, with and without DCMU.
   Explain why oxygen is no longer released when DCMU is added to chloroplasts in white light.3 marks