Science STD 7 Chapter 1: Nutrition in Plants - Exercises

Science STD 7 Chapter 1: Nutrition in Plants - Exercises

1. Why do organisms take food?

All living organisms need to take food to get energy for growth, to build and repair their bodies, and to carry out life processes. The components of food called nutrients are essential for these functions.

2. Distinguish between a parasite and a saprotroph.

Parasite Saprotroph
A parasite is an organism that takes ready-made food from a living host plant on which it climbs. A saprotroph is an organism that takes nutrients from dead and decaying matter.
It uses the heterotrophic mode of nutrition. It uses the saprotrophic mode of nutrition.
Example: Cuscuta (Amarbel) lives on a host plant. Example: Fungi like mushrooms grow on rotting wood or moist soil.

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

The presence of starch in leaves can be tested by performing an iodine test. The leaf is first boiled in alcohol to remove chlorophyll. Then, a few drops of iodine solution are added to the leaf. If starch is present, the leaf will turn blue-black. If starch is not present, it will remain brown. A leaf kept in sunlight will test positive for starch, while a leaf kept in the dark for 72 hours will test negative.

4. Give a brief description of the process of synthesis of food in green plants.

The process of food synthesis in green plants is called photosynthesis. Leaves are the food factories of plants. All the necessary raw materials, such as water, carbon dioxide, and minerals, must reach the leaves. Water and minerals are absorbed by the roots and transported to the leaves through vessels. Carbon dioxide from the air is taken in through tiny pores called stomata on the leaf surface. The leaves have a green pigment called chlorophyll that captures energy from sunlight. This energy is used to synthesise food from carbon dioxide and water. The process can be represented in an equation: Carbon dioxide + water → Carbohydrate + oxygen (in the presence of sunlight and chlorophyll).

5. Show with the help of a sketch that plants are the ultimate source of food.

Plants are the ultimate source of food for all living organisms. We can show this with a simple food chain sketch. All animals, including humans, are directly or indirectly dependent on plants for food. For example, a deer eats grass, and a lion eats the deer. Thus, the lion is indirectly dependent on the plant.

6. Fill in the blanks:

  1. (a) Green plants are called autotrophs since they synthesise their own food.
  2. (b) The food synthesised by plants is stored as starch.
  3. (c) In photosynthesis solar energy is absorbed by the pigment called chlorophyll.
  4. (d) During photosynthesis plants take in carbon dioxide and release oxygen gas.

7. Name the following:

  1. (i) A parasitic plant with yellow, slender and branched stem.

    Cuscuta (Amarbel)

  2. (ii) A plant that is partially autotrophic.

    Pitcher plant

  3. (iii) The pores through which leaves exchange gases.

    Stomata

8. Tick the correct answer:

  1. (a) Cuscuta is an example of:
    1. autotroph
    2. parasite
    3. saprotroph
    4. host
  2. (b) The plant which traps and feeds on insects is:
    1. Cuscuta
    2. china rose
    3. pitcher plant
    4. rose

9. Match the items given in Column I with those in Column II:

Column I Column II
Chlorophyll Leaf
Nitrogen Rhizobium
Cuscuta Parasite
Animals Heterotrophs
Insects Pitcher plant

10. Mark 'T' if the statement is true and 'F' if it is false:

  1. (i) Carbon dioxide is released during photosynthesis. (F)
  2. (ii) Plants which synthesise their food are called saprotrophs. (F)
  3. (iii) The product of photosynthesis is not a protein. (T)
  4. (iv) Solar energy is converted into chemical energy during photosynthesis. (T)

11. Choose the correct option from the following:

Which part of the plant takes in carbon dioxide from the air for photosynthesis?

  1. Root hair
  2. Stomata
  3. Leaf veins
  4. Petals

12. Choose the correct option from the following:

Plants take carbon dioxide from the atmosphere mainly through their:

  1. roots
  2. stem
  3. flowers
  4. leaves

13. Why do farmers grow many fruits and vegetable crops inside large greenhouses? What are the advantages to the farmers?

Growing plants inside large greenhouses allows farmers to control the environmental conditions, which helps them to protect the crops from extreme weather and maintain a consistent temperature for optimal growth.

The advantages to the farmers include:

  • The greenhouse provides protection for crops from extreme weather conditions like strong winds, cold, and excessive heat.
  • It helps maintain a consistent temperature and moisture level, which is beneficial for plant growth.
  • By regulating factors like light, water, and carbon dioxide, farmers can create ideal conditions for photosynthesis and increase crop yield.

Suggested Activities

1. Project: Take a potted plant with broad leaves. Take two strips of black paper and cut out a small square in the centres. Cover a part of two leaves with these papers and secure them with paper clips (Fig. 1.9). Keep the plant in sunlight for 2-5 days. Observe the difference in the colour of the covered and the uncovered portions on the leaf. Perform iodine test on this leaf. Did the two parts show different results? Now take second leaf. Remove the strip and expose the covered part to the sunlight for 2-3 days and do the iodine test again. Describe your observations.

Aim: To demonstrate that sunlight is necessary for photosynthesis to produce starch in leaves.

Procedure Outline:

  1. Cover a small portion of a leaf on a potted plant with black paper and leave the plant in sunlight for a few days.
  2. Perform the iodine test on this leaf. The covered portion will test negative for starch (remain brown), while the uncovered portion will test positive (turn blue-black). This shows that the part of the leaf that did not receive sunlight could not perform photosynthesis and hence did not produce starch.
  3. Expose the previously covered part of the second leaf to sunlight for a few days and repeat the iodine test. It will now test positive for starch, proving that the leaf can produce food once it receives sunlight again.