In an experiment to investigate a factor affecting photosynthesis, a leaf of a potted plant which had been kept in the dark overnight was covered with aluminum foil as shown in the diagram below.
The set up was kept in sunlight for three hours after which a food test was carried out on the leaf.
(a) Which factor was being investigated in the experiment?
(b) What food test was carried out?
c) (i) State the results of the food test.
(ii) Account for the results in c (i) above
(d) Why was it necessary to keep the plant in darkness before the experiment?
Answer:
a)-Light intensity.
b)-Test for starch.
c) i)The covered part of the leaf remains brown/yellow or/retains the color of iodine,
and the uncovered parts turned blue-black.
ii)Photosynthesis occurred and starch
was formed in the uncovered part of the leaf because of the presence of light; while starch was not formed in the covered part of the leaf ( because of lack of light) hence photosynthesis did not occur.
d)-To de-starch the leaf or use up all starch in the leaf.
b)-Test for starch.
c) i)The covered part of the leaf remains brown/yellow or/retains the color of iodine,
and the uncovered parts turned blue-black.
ii)Photosynthesis occurred and starch
was formed in the uncovered part of the leaf because of the presence of light; while starch was not formed in the covered part of the leaf ( because of lack of light) hence photosynthesis did not occur.
d)-To de-starch the leaf or use up all starch in the leaf.
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Explain what would happen to red blood cells if they are placed in a concentrated salt solution. 
