In an investigation of the light-dependent stage of photosynthesis (the Hill reaction), chloroplasts are isolated from fresh spinach leaves.
During the initial extraction (homogenisation), the leaves are ground in an ice-cold, physiologically isotonic sucrose buffer solution. After centrifugation, the supernatant is discarded, and the pellet containing chloroplasts is resuspended in a pH-regulated buffer solution that does not contain sucrose (representing a hypotonic medium) prior to the addition of the redox dye DCPIP.
Explain:
Why an isotonic sucrose solution is used during the initial homogenisation stage of isolation.
Why a buffer solution without sucrose (hypotonic) is used to resuspend the pellet for 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.