Question

The figure given below is for performing an experiment on photosynthesis.

Answer the following:
(i) What is the aim of this experiment?
(ii) Describe an experiment to show that light is necessary for photosynthesis.
(iii) What do you conclude from this experiment?
(iv) What is the role of light in photosynthesis?

Answer 1

1. To demonstrate that sunlight is necessary for photosynthesis.
2. Take a potted plant and keep it for 2-3 days in dark to destarch its leaves. Take one leaf and cover it on both sides with two black paper strips, as shown in the diagram, with the help of cellophane tape. Now keep the potted plant in light. After a few hours pluck the leaf and remove the black strips. Boil the leaf in alcohol and wash it in water. Test the leaf for starch with iodine solution. The leaf turns blue all over except the region covered with black stripes. This shows that the region which did not receive light could not synthesise starch. Thus, light is necessary for photosynthesis.
3. Light is necessary for photosynthesis.
4. Light supplies energy in the form of photons to split water during tight reaction.