Nutrition in Plants - NCERT Guide Science Class 7

Q1: Why do organisms need to take food?

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Ans:Food is required by all living organisms mainly for four reasons or purposes:

• Food helps a living organism to grow. If enough food is not given or if, the food given is not of right kind, the organism will not have proper growth.
• Another important function of food is to provide energy which is required for any living organism for movements and other activities.
• Food is also needed by living organisms for replacement and repairing of their damaged parts.
• Food provide us the power to fight against infections and diseases.

Q2:Distinguish between a parasite and a saprotroph.

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Ans:

Parasite	Saprotroph
A parasite takes readymade food from the organism on which it feeds. They feed on a living organism. The organism on which it feeds is called host. It deprives the host of valuable nutrients.	They secrete the digestive juices on the matter they live and convert it into a solutionand then absorb it. They feed on dead and decaying organism. They do not feed on a living organism. There is no host at all.

Q3: How would you test the presence of starch on leaves?

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Ans:The presence of starch on leaves can be tested by Iodine Test. Iodine turns starch solution blue.

Q4: Give a brief description of the process of synthesis of food in green plants.

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Ans:Leaves have a green pigment called chlorophyll. In presence of sunlight, they use carbon dioxide and water to synthesize carbohydrate. During this process oxygen is released. The carbohydrates ultimately get converted into starch.
Carbon dioxide from air is taken through stomata. Water and minera;ls are absorbed by roots and transported to leaves.