The light-dependent reactionAQA A-Level Biology: Mind map

Exam questions on The light-dependent reaction

1. In the thylakoid membranes of a chloroplast, light energy absorbed by chlorophyll causes the chlorophyll to release electrons. The chlorophyll must then be supplied with replacement electrons so that it can go on absorbing light.
   Explain why chlorophyll needs a supply of replacement electrons and state where they come from.2 marks
2. Isolated chloroplasts were illuminated in a solution that contained no carbon dioxide but did contain an artificial electron acceptor. Oxygen was released while the chloroplasts were in the light.
   Explain why oxygen release would stop if the chloroplasts were placed in the dark.2 marks
3. A student extracted chloroplasts from leaves in ice-cold isotonic buffer. She added a sample to a solution of DCPIP, a blue dye that becomes colourless when it is reduced, and measured the absorbance of the mixture. In a tube in the light, the absorbance fell from 0.80 to 0.20 over 12 minutes. In a tube kept in the dark it fell from 0.80 to 0.78, and in a tube containing boiled chloroplasts in the light it fell from 0.80 to 0.79.
   Calculate the rate of change of absorbance in the tube in the light. Give your answer in absorbance units per minute.3 marks