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A plant is kept in the dark for two days. A leaf is used in an experiment to investigate the effect of two factors on photosynthesis as shown in the diagram.

What are the colours of Q and R, when the leaf is tested for starch, using iodine solution?

(a) Blue/blckBrown
(b) BrownBrown
(c) Blue/blackBlue/black
(d) BrownBlue/black

A. (a) B. (b) C. (c) D. (d)

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For photosynthesis to occur, both sunlight and CO2 are required. The plant forms glucose (later on converted to starch) through photosynthesis. The part Q of leaf was covered and not exposed to light and part R was kept in absence of CO2. Thus, both parts of leaf did not form starch and gave a negative test for starch. (Note - iodine solution gives a positive test for starch and turns blue-black in colour)

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