K.C.S.E Biology Q & A - MODEL 1998PP1QN14

K.C.S.E Biology Q & A - MODEL 1998PP1QN14

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?

ANSWERS

(a) Light; Rej:  light intensity
(b) Test for starch
(c) (i) The covered part of the leaf remain brown/yellow/ retain color of iodine, and the uncovered parts turned blue/ black; rej blue  alone black  alone.
(ii) Starch was formed in the covered part of the leaf  (because of the  presence);  while starch was  not formed in the covered part of the leaf ( because of lack light)
(d) To destarch the leaf;