ATP and the light-dependent reactionsEdexcel A-Level Biology A: Mind map

Exam questions on ATP and the light-dependent reactions

1. A resting adult holds only about 50 g of ATP in the whole body at any moment, yet turns over roughly their own body mass of ATP in a day. A student reading about this wants to understand how a cell can use so much ATP while storing so little.
   Using the information given, explain why a cell must continually resynthesise ATP.2 marks
2. A student investigates the light-dependent reactions using isolated chloroplasts suspended in a cold, buffered solution. The suspension is mixed with DCPIP, a blue dye that is colourless when reduced and that can accept electrons in place of NADP. No carbon dioxide is supplied. One tube is placed in bright light and an identical tube is wrapped in foil.
   Explain why the DCPIP in the illuminated tube changes from blue to colourless.2 marks
3. In 1966 the biochemist André Jagendorf soaked isolated chloroplasts in an acidic buffer at pH 4 until the space inside the thylakoids was also at about pH 4. He then moved them, in complete darkness, into a buffer at pH 8 that contained ADP and inorganic phosphate (Pi). The chloroplasts made ATP for a short time and then stopped.
   Suggest how the chloroplasts made ATP in the dark in this experiment.3 marks