Answer the following questions in your own words.
(a) Why do living organisms need nutrition ?
(b) Explain the process of production of food in plants.
(c) What is meant by parasitic plants ? Name their different types with examples of each.
(d) Explain the various steps of nutrition in animals.
(e) Name some unicellular organisms in which all life-processes take place within their unicellular body.


a. Nutrition is the process of uptake of nutrients from food and utilizing them for various functions of the cells. Nutrition is required for purposes like:
  • supplying the energy required for doing work
  • for growth and development of the body
  • to fight diseases
  • to replace the damaged cells and repair tissues

b. Leaves are the food factories of plants. They are the sites where the synthesis of food occurs in plants. The leaves of plants contain a green pigment called chlorophyll. This pigment captures the sun’s energy, which is used to prepare food from carbon dioxide and water. The process of synthesis of food using sunlight, carbon dioxide, and water is known as photosynthesis. During the process of photosynthesis, the leaves containing chlorophyll convert carbon dioxide and water into carbohydrates in the presence of sunlight. Carbohydrates, which are produced during photosynthesis, are ultimately converted into starch to be stored in plants.This process can be represented in the form of the following equation:

c. Cuscuta survives by growing on the body of another plant and deriving nutrients from this plant in the process. This mode of nutrition is known as parasitic mode of nutrition. Cuscuta is known as a parasite as it depends on another plant for its survival. The plant on which it grows is known as the host. Cuscuta can be seen around in the form of yellow tubular structures growing on the stems of other plants. It is devoid of leaves. Another such example of parasitic plants is Loranthus.

 d.  The various steps of nutrition in animals are:
  • Ingestion − The process of taking in of food into the body is called ingestion. Ingestion of food in humans is done with the help of the buccal cavity. 
  • Digestion − The process where conversion of food into soluble form occurs.
  • Absorption − The nutrients from the digested food are absorbed in the small intestine with the help of finger-like projections called villi.
  • Assimilation − The absorbed nutrients are transported via the blood vessels to the different organs, to be utilised for different life processes. 
  • Egestion − The process of removal of faecal matter through the anus is called egestion. 

e. The unicellular organisms in which all life processes take place within their body are- Amoeba, Paramoecium and Euglena.

General Science (Solutions)
Standard VII

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