Class 7 Nutrition in Animals
Modes of Nutrition
The methods of obtaining food are called modes of nutrition.
There are mainly two modes of nutrition :
1. Autotrophic Nutrition
2. Heterotrophic Nutrition.
Autotrophic mode of Nutrition
Green plants take carbon dioxide and water from the environment and transform them into glucose and oxygen with the help of sun’s energy, trapped by a green pigment called chlorophyll.
Those organisms which can make food themselves from simple substances by the process of photosynthesis are called autotrophs, and their mode of nutrition is called autotrophic nutrition. These green plants produce food not only for themselves, they also make food for nongreen plants as well as for animals (including
What is the Heterotrophic mode of Nutrition?
Those organisms which cannot make food themselves by the process of photosynthesis and take food from green plants or animals are called heterotrophs, and their mode of nutrition is called heterotrophic nutrition.
All non-green plants and animals (including human beings) are heterotrophs. Heterotrophic plants and animals depend on food produced by some other living organisms such as green plants for example; Cuscuta, many bacteria and fungi depend for their nutrition on the bodies of other plants and animals. Thus, all animals like cats, dogs, goats, cows, buffaloes, deer, lions and human beings are heterotrophs having a heterotrophic mode of nutrition.
What is Photosynthesis?
The process by which green plants make their own food (such as glucose) from carbon dioxide and water by using sunlight in the presence of chlorophyll is called photosynthesis. The process of photosynthesis can be represented by a word equation as follows :
Oxygen gas is released during photosynthesis. This oxygen goes into the air. The oxygen gas released in photosynthesis is utilised by all the living organisms for their survival. The process of photosynthesis can be shown with the help of a diagram
Photosynthesis cannot occur in the absence of any one of these conditions. We will now describe how the leaves of a
plant get carbon dioxide and water required for making food by photosynthesis and what are the roles of chlorophyll and sunlight in photosynthesis.
Conditions Necessary for Photosynthesis
The conditions necessary for photosynthesis to take place are :
3. Carbon dioxide, and
1. How do plants obtain carbon dioxide for photosynthesis:
Plants take carbon dioxide gas from the air with the help of tiny pores (called stomata) present on the surface of leaves. (The singular of stomata is stoma). Each pore (stoma) is surrounded by a pair of guard cells. The opening and closing of stomatal pores in leaves is controlled by the guard cells as shown in figure, shows open
stomatal pores whereas fig (3b), shows the stomatal pores in closed positions. The carbon dioxide gas present in air enters the leaves of a plant through the stomatal pores present on their surface and is utilised in
photosynthesis. The oxygen gas produced in the leaves during photosynthesis goes out into the air through the same stomatal pores. The stomatal pores of leaves open only when carbon dioxide is to be taken in or oxygen is to be released otherwise they remain closed.
3. Fibres from animals
6. Physical And Chemical Change
7. Weather, Climate and Adaptations
8. Winds, Storms and Cyclones
13. Motion and Time