Question

A student carried out an experiment to investigate the conditions necessary for photosynthesis. He fixed leaf 'A' of a potted plant into a flask containing potassium hydroxide solution. He fixed another leaf 'B' of the plant into a flask containing water and wrapped the flask with a piece of black cloth. The plant was left in sunlight. After 6 hours he detached and tested both leaves for starch. Which of the following results most likely the student had found?

• A. Starch was found in both leaves A and B.
• B. Starch was found in leaf A but not in leaf B.
• C. Starch was found in leaf B but not in leaf A.
• D. Starch was not found in any leaves.

Answer 1

The correct option is D Starch was not found in any leaves.

The leaf of the potted plant was covered with a piece of black cloth to destarch it. Potassium hydroxide solution is to absorb the carbon dioxide gas from the air present in the glass bottle so that no carbon dioxide is left in the air inside the glass bottle. He will find that the leaf which was inside the glass bottle having no carbon dioxide around it, does not turn blue on adding iodine solution showing that no starch is present in this leaf. From this observation, we conclude that the photosynthesis to make starch in the leaf does not take place without carbon dioxide. And by covering the flask containing leaf B with black cloth, the leaf wont get exposure of sun light and photosynthesis won't happen. From this observation, we conclude that photosynthesis (to make starch) takes place in the presence of sunlight. Hence both the leaves do not have starch.