Question

An experiment was set up as shown in the adjoining figure. The twig in the diagram was intact on the plant and it was left as such in sunlight for a few hours.
(i) What is the aim of the above experiment?
(ii) Why was potassium hydroxide placed inside the conical flask?
(iii) What test would you perform on the leaf inside the flask?
(iv) What is the expected result of the above test?
(v) Is it necessary to similarly test on outer leaf also? Give a reason.
Figure

Answer 1

(i) The aim of the experiment is to show that carbon dioxide is necessary for photosynthesis.

(ii) Potassium hydroxide is placed inside the conical flask to absorb all the carbon dioxide present in it.

(iii) Iodine test should be performed on the leaf inside the flask.

(iv) Photosynthesis does not occur in the absence of carbon dioxide; therefore, no starch will be formed. As a result, there will be no change in the colour of the leaf.

(v) Yes, it is necessary to similarly test on the outer leaf also to show the presence of starch. Outer leaves can take carbon dioxide from the atmosphere and carry out photosynthesis and make starch. Hence, they will give positive iodine test. This will help us in confirming that the leaf inside, gives negative results for iodine test due to absence of photosynthesis.