U.C.E BIOLOGY 2004 PAPER 1 QN 32

To investigate the effect of carbon dioxide on photosynthesis, a green plant was destarched by leaving it in darkness for 24 hours. After destarching, leaf A was put in a conical flask as shown in figure 2 while leaf B was immediately tested for starch. The set up was then left in light for 12 hours after which leaves A and C were tested for starch.

a) Why was sodium hydroxide used in the experiment?

b) State two reasons why when the plant was placed in darkness for 24 hours it became destarched.

c) State the purpose of including each of leaves B and C in the experiment.

(i) Leaf B ………………………………………………………………………………………..

(ii) Leaf C ………………………………………………………………………………………..

d) What was observed when each of leaves A, B and C were tested for starch?

(i) Leaf A ……………………………………………………………………………………..

(ii) Leaf B ……………………………………………………………………………………..

(iii) Leaf C ……………………………………………………………………………………

e) Give reasons why each of the following is carried out while testing a leaf for starch.

(i) Put a leaf in boiling water.

(ii) Put a leaf in hot ethanol.

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