Tuesday, 14 June 2011

Nutrition in Plants : Lesson 1 :: NCERT Class VII (7th) Science Exercises Solution


1.Question :  Why do organisms need to take food?

Answer : All living organisms require food to get essential nutrients like carbohydrates, proteins, fats, vitamins and minerals  which are necessary for theirs growth, maintenance of body and reproduction.
2.Question : Distinguish between a parasite and a saprotroph.
Answer : 
Parasite : Some organisms for theirs requirement of food  nutrients which are must for  their survival, growth and reproduction, depend on the food produced by other living organism called host. Such living organism which deprives the host of valuable nutrients, is called a parasite
Saprotrophs: Some organisms like fungi, have a different mode of nutrition.They secrete digestive juices on the dead and decaying matter and convert it into a solution. Then they absorb the nutrients from it. This mode of nutrition in which organisms take in nutrients in solution form from dead and decaying matter is called saprotrophic nutrition. Plants which use saprotrophic mode of nutrition are called saprotrophs.

3. How would you test the presence of starch in leaves?
Answer : We can test the presence of starch in leaves by performing iodine test. To test the presence of starch in leaves take leave from the plant which has been kept outside or exposed to sunlight.  Boil the leave in water for 2 to 3 minutes to soften it and then place the leave in a test tube containing Ethanol or Alcohol. Now place the test tube in a beaker containg water and gently heat the beaker till the alcohol dissolves in the chrolophyll and the leaves loses its green colour. Wash the leaf with water and then spread the leaf out on a white plate and add a few drops of iodine solution.The parts of leave  that turn blue black show the presence of starch..

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

Answer : The synthesis of food in green plants is the chemical process in which plants make  food in the presence of sun light using a green pigment present in leaves called chlorophyll. It helps leaves to capture the energy of the sunlight. This energy is used to synthesise (prepare) food from carbon dioxide and water. Since the synthesis of food occurs in the presence of sunlight, it is called photosynthesis. During the process of photosynthesis, plants make starch(glucose) and oxygen. The starch  is used by plants as energy for converting nutrients and minerals into into other organic compounds which are must to grow, to replace worn out cells, to get rid of waste, and to reproduce.The  oxygen so produced, is released in air which is consumed by other living being for their survival.

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

6. Fill in the blanks:
(a) Green plants are called autotrophs since they synthesise their own food.
(b) The food synthesised by the plants is stored as carbohydrate or starch.
(c) In photosynthesis solar energy is captured by the pigment called chlorophyll.
(d) During photosynthesis plants take in carbon dioxide  and release oxygen.
7. Name the following:
(i) A parasitic plant with yellow, slender and tubular stem. - Cuscuta (Amarbel)
(ii) A plant that has both autotrophic and heterotrophic mode of nutrition. -insectivorous plants
(iii) The pores through which leaves exchange gases - stomata

8. Tick the correct answer:
(a) Amarbel is an example of:(i) autotroph (ii) parasite (iii) saprotroph (iv) host
Answer : Amarbel is an example of  parasite .

(b) The plant which traps and feeds on insects is:
(i) cuscuta (ii) china rose (iv) pitcher plant (iv) rose
Answer : The plant which traps and feeds on insects is pitcher plant
9. Match the items given in Column I with those in Column II:
  Column I                                    Column II
  Chlorophyll                                Bacteria
  Nitrogen                                    Heterotrophs
  Amarbel                                    Pitcher plant
  Animals                                     Leaf
  Insects                                      Parasite

Answer : Matched Items Column wise
  Column I                                 Column II
  Chlorophyll                             Leaf
  Nitrogen                                 Bacteria
  Amarbel                                 Parasite
  Animals                                  Heterotrophs
  Insects                                   Pitcher plant

10. Mark ‘T’ if the statement is true and ‘F’ if it is false:
(i) Carbon dioxide is released during photosynthesis. (F)
(ii) Plants which synthesise their food themselves are called saprotrophs. (F)
(iii) The product of photosynthesis is not a protein. (F)
(iv) Solar energy is converted into chemical energy during photosynthesis. (T)

11. Question : Choose the correct option from the following:

Which part of the plant gets carbon dioxide from the air for photosynthesis.
(i) root hair (ii) stomata (iii) leaf veins (iv) sepals
Answer :  Stomata

12. Question : Choose the correct option from the following:
Plants take carbon dioxide from the atmosphere mainly through their:
(i) roots (ii) stem (iii) flowers (iv) leaves
Answer : leaves

A Little beyond lesson ....
What Product Plants Makes Out Of Photosynthesis
As you know the the plants in the presence of sun light , using chlorophyll, water, carbon dioxide make  food for themselves. In this process  Carbohydrates are the most essential and important direct organic product of photosynthesis in the majority of green plants. This process of Photosynthesis in plants leading to the formation of a simple carbohydrate is shown in the given chemical equation :-

                                           ( Sun Light )
6CO2           +  12H2O ------------------------>C6H12O6  + 6O2  +  6H2O
                                          ( Chlorophyll )
Carbon Dioxide        Water                                            Glucose       Oxygen      Water        


Little free glucose is produced in plants; instead, glucose units are linked together to form starch or are joined with fructose, another sugar, to form sucrose (see carbohydrate).

Not only carbohydrates, as was once thought, but also amino acids, proteins, lipids (or fats), pigments, and other organic components of green tissues are synthesized during photosynthesis.