Textbook Solutions: Nutrition in Plants | Class 7 Oxford Science: Chapter Notes, Worksheets & Tests PDF Download

A. Choose the correct option.

B. Fill in the blanks with the correct words. 

1.
Ans:  Nutrition refers to the process by which an organism takes in food and uses it to produce energy.

2. 
Ans: Chlorophyll is the green pigment present in the leaves of plants.

3. 
Ans: The phloem carries food produced in the leaves to all parts of the plant.

4.
Ans: Saprophytic plants obtain food from other green plants.

5.  
Ans: Saprophytic plants usually grow in soils deficient in nitrogen.

6.
Ans: In a symbiotic relationship, both members mutually benefit from each other.

C. Name the following. 

1.
Ans: Autotrophs

2.
Ans: Saprophytes

3.
Ans: Symbiosis

4.
Ans: Fertilizer

D. Answer the following questions. 

1.
Ans: Food is any substance that can be broken down into simpler substances to produce energy and support growth and repair of bodily tissues. Living things need food because it provides the energy required for carrying out daily activities like breathing, walking, running, playing, and studying. It also enables growth and repair of body tissues. 

2.
Ans: Autotrophic nutrition is the mode of nutrition where organisms make their own food, as seen in green plants that carry out photosynthesis. Heterotrophic nutrition is the mode of nutrition where organisms depend upon other plants and animals for food. For example, animals like cows, goats, lions, and tigers, and certain plants that lack the photosynthetic pigment are heterotrophs.

3.
Ans: Photosynthesis is a process in which green plants use the sun's energy to convert water and carbon dioxide into carbohydrates such as glucose. The glucose is then converted to starch for storage. The byproduct, oxygen, is released into the atmosphere. For photosynthesis to occur, four conditions need to be met: presence of Chlorophyll (the green pigment that traps light energy), Sunlight (the main source of energy), Air (specifically carbon dioxide), and Water.

4.
Ans: In photosynthesis, water and carbon dioxide are converted into glucose and oxygen under the influence of sunlight and with the help of chlorophyll. Water is absorbed by the roots from the soil and transported to the leaves through the xylem. Carbon dioxide is obtained from the air through stomata in the leaves. Sunlight is absorbed by the chlorophyll in the leaves. The energy is used to convert the water and carbon dioxide into glucose and oxygen. The oxygen is released into the atmosphere and the glucose is converted into starch for storage.

5.
Ans: The word equation for photosynthesis is: Sunlight + Carbon dioxide + Water -> Glucose + Oxygen.

6.
Ans: Xylem and phloem are special structures in plants that help transport water, nutrients, and sugar. Xylem carries water and soluble minerals from roots to the leaves. Phloem carries the sugar produced by photosynthesis from the leaves to other parts of the plant.

7.
Ans: (i) Parasitic plants: These are plants that absorb food from other green plants (their hosts), such as Cuscuta (Dodder) and mistletoe.
(ii) Symbiotic plants: These plants exist in mutually beneficial relationships with other organisms. For example, Rhizobium bacteria and leguminous plants.
(iii) Saprophytic plants: These plants absorb nutrition from dead or decaying organic matter, like Indian Pipe and coral root.

8.
Ans: Insectivorous plants are plants that trap and digest insects in order to fulfill their nutrient requirements, especially when they grow in nutrient-deficient soils. Examples include the pitcher plant and the Venus flytrap.

9.
Ans: The pitcher plant traps insects using its leaf that is modified to form a pitcher-like structure. The inside of this structure has sticky hairs which trap the insect and prevent it from escaping. Digestive juices present at the bottom of the pitcher digest the trapped insect.

10.
Ans: Nitrogen can be added back into the soil through the use of manures and fertilizers, and through nitrogen fixation. Manures and fertilizers are rich in nutrients and are added to the soil by farmers to replenish the nutrients. Nitrogen fixation is a natural method where bacteria like Rhizobium convert atmospheric nitrogen into a form that can be used by plants. Farmers grow leguminous plants alternately with other crops to replenish the nitrogen content of the soil through this process.