How to show experimentaly
that photosynthesis is
necessary for plants..
Answers
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 s5mthesize 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
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.
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.