Question

The following diagram demonstrates a physiological process taking place in green plants. The whole setup was placed in bright sunlight for several hours. Study the diagram and answer the questions that follow:

(i) What aspect of the physiological process is being examined?
(ii) Explain the physiological process mentioned in (i) above.
(iii) Why watch-glass containing potassium hydroxide is kept in A?
(iv) Write a well-balanced chemical equation for the physiological process explained in (ii) above.
(v) What would be the result of the starch test in the case of plant A and plant B?

Answer 1

(i) Aspect of the physiological process being examined

1. In the diagram, the necessity of carbon dioxide in photosynthesis is examined.
2. The physiological process examined in the given figure is photosynthesis.

(ii) Photosynthesis:

1. Photosynthesis refers to the process by which green plants synthesize food carbon dioxide and water in the presence of chlorophyll and light energy.
2. Photosynthesis takes place in the chloroplast that is present in the mesophyll cells of the leaves.
3. During photosynthesis, light energy from the sun is trapped by chlorophyll which is then utilized for glucose production from raw materials (water and carbon dioxide).
4. In addition, oxygen is released into the atmosphere as a waste product.

(iii) Role of potassium hydroxide in A:

1. In the experiment, a watch glass containing potassium hydroxide is kept in A to absorb carbon dioxide.

(iv) The chemical equation of Photosynthesis:

$$\begin{gathered} 6{\mathrm{CO}}_2+6{\mathrm{H}}_2\mathrm{O}\underset{\mathrm{Chlorophyll}}{\overset{\mathrm{Sunlight}}{\to }}{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6+6{\mathrm{O}}_2 \\ \mathrm{Carbon}\mathrm{Water}\mathrm{Glucose}\mathrm{Oxygen} \\ \mathrm{dioxide} \end{gathered}$$

(v) Starch test:

1. In the leaves, excess glucose is rapidly converted into starch. The starch test is used to test the presence of carbohydrates in leaves.
2. In the case of plant A, photosynthesis will not occur due to the presence of potassium hydroxide.
3. Potassium hydroxide will absorb CO₂ which is one of the raw materials for glucose production. The leaves will not turn blue-black after the starch test.
4. In the case of plant B, photosynthesis will occur since there’s no potassium hydroxide present inside the glass jar.
5. Leaves will utilize CO₂ and synthesize glucose. Here, the leaves will turn blue-black as a result of the starch test.