A technician takes a geranium plant directly from a brightly lit greenhouse. One leaf is sealed in a flask containing soda lime, which absorbs carbon dioxide. The plant is left in the light for one day. The leaf is then tested with iodine solution and turns blue-black.
Why does this result not show that carbon dioxide is unnecessary for photosynthesis?
the chlorophyll may have made iodine solution blue-black without any starch
the soda lime may have supplied carbon dioxide while the leaf was in the flask
the blue-black colour may have been caused by oxygen released from the leaf
the starch detected may have been made before the leaf entered the flask
117 exam-style questions on OCR GCSE Biology 1.4 Photosynthesis, covering 1.4.1 Photosynthesisers as biomass producers, 1.4.2 Factors affecting the rate of photosynthesis, and 1.4.3 Limiting factors in photosynthesis. Each one has a worked solution and a mark scheme showing where the marks go.