Question

3.Write an activity to show that sunlight is necessary for photosynthesis.
4.Write an activity to show that carbondioxide is necessary for photosynthesis.
5. What is the role of KOH solution in the above experiment?
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Answer 1

Explanation:

Experiment to Prove Light is Essential for Photosynthesis!

Experiment:

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.

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

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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.

The rate of photosynthesis is the maximum in the presence of red and blue lights, while in green light the rate is minimum because green light is reflected by the chlorophyll molecules.

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

1. Take a plant with destarched leaf. Leaf is partially covered with black paper on which a design is cut. Expose this plant to sunlight for few hours and perform a starch test with iodine solution.
2. Insert a part of the leaf of a destarched plant into a conical flask containing potassium hydroxide. Potassium hydroxide solution absorbs the carbon dioxide gas from the air present in the glass bottle. Leave the plant sunlight. After few hours, perform a starch test to this and another leaf of the same plant.
3. Potassium hydroxide is used in the experiment for the absorption of CO2 from the plant released during respiration. When KOH absorbs CO2, it creates a vacuum in the flask. The air present in the bent glass tube moves into the conical flask. This pulls the water in the bent tube further up.

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