V. Answer the following questions in about four to five sentences.

1. How do leaves help a plant make its food?

Ans: Photosynthesis occurs in the cells of leaves. The cells contain chloroplasts where a green pigment present called chlorophyll. The chlorophyll traps the energy from sunlight. With the help of carbon di oxide entered through the stomata and the water, the photosynthesis takes place in the leaves to make food.

2. How does saprophyte obtain nutrition?

Ans: The saprophytes feed on dead organic matter. The saprophyte grows on organic matter. It secrets digestive juices. The digestive juices break down organic matter into simple substances and convert it into solution. The saprophyte absorbs the solution and obtain nutrition.

3. How do bean plants enrich the soil?

Ans: The bacteria called Rhizobium present in the roots of the bean plants which takes up the nitrogen from the air and convert it into water soluble nitrogenous substances. When the plants die and decay the nitrogenous substances mix into the soil and make the soil fertile.

4. Differentiate between total and partial parasitic plants.

Ans: 

Total parasitic plants: a. They don't have chlorophyll. Therefore they cannot make their food.

b. They depends completely on the host plant for food and water.

c. The kill the host plant slowly.

Partial parasitic plants: a. They have chlorophyll. Therefore they can make their food.

b. They depends on the host plant only for the water and minerals.

c. The do not kill the plants.

5. How are parasitic plants different from saprophytes?

Ans: The parasitic plants are different from saprophytes. The parasitic plants get their nutrition from the host plants. On the other hand the saprophytes get their food from dead organic matter. 

6. How would you test the presence of starch in leaves?

Ans: Test for the presence of starch in leaves:

1. Firstly some water is boiled and a green leaf is placed for about 3 minutes. Then the leaf is taken out and placed it in a test tube and ethanol is added. After this the test tube is placed in boiling water and let the alcohol to be boiled.

2. The chlorophyll will be dissolved in the alcohol. The leaf will turn colourless.

3. After washing the leaf with tap water, dilute solution of iodine is poured over the leaf. The leaf will turn bluish in colour.

4. This proves that the starch is present in the leaves. Because iodine and starch react and develop the bluish colour.