NUTRITION IN PLANTS (Part - 2), Class 7

 NUTRITION IN PLANTS


Q.8. Fill in the blanks: 

(a) Green plants are called _________________ since they synthesise their own food. 

(b) The food synthesised by plants is stored as _________________. 

(c) In photosynthesis, solar energy is absorbed by the pigment called ___________. 

(d) During photosynthesis, plants take in ______________________ and release __________________ gas.

Ans. (a) autotrophs

         (b) starch

         (c) chlorophyll

         (d) carbon dioxide, oxygen

Q.9. What are the raw materials required for the process of photosynthesis and write role of each.

Ans. i) Sunlight: It acts as a source of energy for the process of photosynthesis. Since all the food on this Earth is made by utilizing solar energy, therefore sun is the ultimate source of energy for all the living organism.

        ii) Chlorophyll: Chlorophyll absorbs light energy from the sun and converts it in chemical energy for breaking of water into hydrogen and oxygen. Chlorophyll is present in every leaf of a plant in the form of hundreds of tiny structures called 'chloroplasts'.

        iii) Carbon dioxide: It enters through stomata and oxygen is released as a by-product through stomata. Carbon dioxide gets reduced to carbohydrates.

        iv) Water: Water carries dissolved minerals like nitrogen, phosphorus etc from roots to leaves.

Q.10. What are cells. Explain their basic structure.

Ans.10. The bodies of living organisms are made of tiny units called cells. 

                                    Cell -> Tissue -> Organ -> Organ system -> Body

Cells can be seen only under the microscope. Some organisms are made of only one cell and hence are called unicellular while others are called multicellular.

The cell is enclosed by a thin outer boundary, called the cell membrane. Most cells have a distinct, centrally located spherical structure called the nucleus. The nucleus is surrounded by a jelly-like substance called cytoplasm.

Q.11. What is stomata? Draw its structure and write its functions.

Ans. Stomata are the tiny pores present on the surface of leaves. These pores are surrounded by ‘guard cells’. One pore is called 'Stoma'.

Functions of stomata are:

  • It helps in exchange of gases.
  • It helps in process of transpiration.


Q.12. Which part of plant performs photosynthesis other than leaves?

Ans. Besides leaves, photosynthesis also takes place in other green parts of the plant — in green stems and green branches. The desert plants have scale- or spine-like leaves to reduce loss of water by transpiration. These plants have green stems which carry out photosynthesis.

Q.13. Does photosynthesis also take place in leaves having colour other than green? Justify your answer.

Ans. The leaves other than green also have chlorophyll. The large amount of red, brown and other pigments mask the green colour. Photosynthesis takes place in these leaves also.

Q.14. What are algae?

Ans.  Algae are a large group of simple, plant-like organisms. They can be seen as slimy, green patches in ponds or stagnant water bodies. The singular of algae is 'alga'. 
They contain chlorophyll which gives them the green colour. Algae can also prepare their own food by photosynthesis.
Algae, however, differ from plants because they do not have proper roots, stems and leaves. 

Q.15. What are the benefits of photosynthesis?

Ans. i) Photosynthesis by plants provides food to animals (including human beings).
        ii) The process of photosynthesis adds oxygen into air.

Q.16. How would you test the presence of starch in leaves?

Ans. The presence of starch in leaves indicates the occurrence of photosynthesis. Starch is also a carbohydrate. The test for presence of starch in leaves can be done by iodine test as follows:
  • Pluck a green leaf from a plant.
  • Boil the leaf in water. This will kill the leaf, disturbs the cell membrane and soften the cell wall.
  • Put it again in test tube containing alcohol and place the test tube with the leaf in the beaker filled with water.
  • Keep the complete setup over the burner and let it boil till all the chlorophyll is removed from the leaf, i.e., the green colour of the leaf disappears.
  • Using forceps, carefully take out the decolourised leaf and wash it in water to remove any chlorophyll sticking to it. 
  • Pour a few drops of iodine solution on the leaf.
  • Appearance of blue-black colour in leaf shows the presence of starch in it. 

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