(a) List the three events that occur during the process of photosynthesis. Explain the role of stomata in this process.(b) Describe an experiment to show that “sunlight is essential for photosynthesis.”


(a) Three events that occur during the process of photosynthesis are:

(i) Absorption of light energy through the chlorophyll pigment.

(ii) Conversion of light energy into chemical energy and splitting of a water molecule into hydrogen and oxygen.

(iii) Reduction of carbon dioxide into carbohydrates.

The main functions of stomata are:

1) Stomata allow the exchange of gases from the surrounding medium.

Usually, carbon dioxide is taken up and oxygen is released.

2) Stomata also helps in transpiration, the loss of excess water from the aerial parts of the plant.

                 

 

(b)

Aim: Sunlight is essential for photosynthesis.

Procedure:

(i) A healthy green potted plant is placed in a dark room for 1 to 2 days to ensure that plant utilizes all reserved food and leaves do not contain any starch.

(ii) Cover a portion of a leaf of this plant (don't pluck this leaf) on both sides with two uniform pieces of black paper using two paper clips.

(iii) After this step, place the plant under bright light.

(iv) After few hours of light exposure, remove the leaf (covered with black paper) and decolorize it using alcohol.

(v) Test the presence of starch (prepared food) with iodine solution.

Observation:

The part of the leaf covered with black paper does not contain starch.

Conclusion:

During the process of photosynthesis, the food prepared by the plants is stored as starch. When starch reacts with the iodine solution, it gives a blue-black color.

The part of the leaf exposed to sunlight can synthesize starch and produce a blue-black color, while the part of the leaf that did not receive sunlight, does not produce starch and thus does not give a blue-black color.

Therefore, it is concluded that sunlight is very essential for the process of photosynthesis.

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Updated on: 18-Jan-2023

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