In an investigation into the electron transport chain of the light-dependent stage of photosynthesis (the Hill reaction), chloroplasts are isolated from the leaves of the maidenhair fern (Adiantum capillus-veneris).
During the extraction process, the leaves are first ground in an ice-cold, physiologically isotonic sorbitol buffer solution. After filtration and centrifugation, the supernatant is discarded, and the pellet containing the chloroplasts is resuspended in a hypotonic phosphate buffer solution containing no sorbitol before the addition of the redox dye DCPIP.
Explain:
Why an isotonic sorbitol solution is used during the initial homogenisation stage of isolation.
Why a hypotonic buffer solution without sorbitol is used to resuspend the pellet prior to initiating the Hill reaction.
16 exam-style questions on OCR A A Level Biology Photosynthesis. Each one has a worked solution and a mark scheme showing where the marks go.