Question

write the necessary steps for setting up the experiment to demonstrate that light is necessary for photosynthesis

Answer 1

Objective:
To show experimentally that light is essential for photosynthesis.

Apparatus and materials required:
A healthy potted plant, a petri dish, a beaker containing water, forceps, a water bath, a piece of wire gauze, a tripod, a burner, a box of matches, alcohol a strip of black paper, iodine solution and clips.

Theory:
Photosynthesis is a biochemical process by which green plants synthesize simple sugar in the presence of sunlight using carbon dioxide from the atmosphere and water from the soil. This simple sugar (glucose) is later converted to starch.
6CO2 + 12H2O ChlorophyII / Sunlight C6H12O6 + 6H2O + 6O2
The most important factor for photosynthesis is light. The rate of photosynthesis depends on the quantity and quality of light. The chlorophyll molecule in green leaves absorb light, get excited and emit electrons. The emitted electrons are used in the production of adenosine triphosphate (ATP). Finally the solar energy is converted into chemical energy and stored in the glucose produced.

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.

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.
3. Boiling the leaf in alcohol should be done in the water bath.