Question

how can you experimentally prove that light is essential for photosynthesis​

Answer 1

Procedure:

1. Take the potted plant and keep it in a dark place for 2-3 days so that the leaves get destarched.

2. Cover a part of one of its leaves with the strip of black paper. Make sure that you cover both the sides of the leaf.

3. Now place this plant in sunlight for 3—4 hours.

4. Pluck the selected covered leaf and remove the black paper covering it.

5. Place this leaf in the beaker containing water and boil it for about 10 minutes.

6. Take out the leaf and now boil it in alcohol, using the water bath, for 10 minutes. This removes the chlorophyll.

7. Take out the leaf and wash it under running water.

8. Place this leaf in the Petri dish and put a few drops of iodine solution on it. Now observe the change in colour.

Exp0eriment to Show that Light is Essential For Photosynthesis

Observations:

The leaf turns blue-black except in the covered region. As this covered region did not receive light, photosynthesis did not occur. Hence no starch was formed there. The uncovered region received light and starch was formed there due to photosynthesis.

Result:

Light is essential for photosynthesis.

Precautions:

1. Before starting the experiment, the leaf must be distracted.

2. The leaf must be covered with black paper properly to prevent the entry of light.

Answer 2

Procedure

Detach the leaves of a potted plant.

Cut a simple shape from a piece of thick cardboard of aluminum foil and fix it onto the upper and lower surface of some of the leaves using paper clips, such that part of the leaf is covered whilst other parts are not covered.

Put the plant in sunlight for three (3) hours.

Remove the cover and test the leaf for the presence of starch.

Observation

The areas covered by the thick cardboard or aluminium foil tested negative for the the presence of starch but the area exposed to the sunlight tested positive for the presence of starch.

The presence of starch in the uncovered portion and it's absence in the covered portion shows that sunlight is necessary for the formation of starch.

As starch is formed by photosynthesis, sunlight must be necessary do photosynthesis.