[Short Notes – E&B] NCERT Class VII – Science – Nutrition in Plants – Chapter 1- Part 1
Science Class 7 – Chapter 1
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Read complete book (must) at : NCERT Class VII – Science – Nutrition in Plants – Chapter 1
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Nutrients
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Carbohydrates, proteins, fats, vitamins and minerals are components of food. These components
of food are necessary for our body and are called nutrients.
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Humans and animals are directly or indirectly dependent on plants as they can’t make their own food.
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MODE OF NUTRITION IN PLANTS
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Plants are the only organisms that can prepare food for themselves by using water, carbon dioxide and minerals.
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The nutrients enable living organisms to build their bodies, to grow, to repair damaged parts of their bodies and provide the energy to carry out life processes.
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NUTRITION
Nutrition is the mode of taking food by an organism and its utilisation by the body.
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The mode of nutrition in which organisms make foodthemselves from simple substances is called autotrophic (auto = self; trophos = nourishment) nutrition.
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Plants are called autotrophs.
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Animals and most other organisms take in ready made food prepared by the plants.
They are called heterotrophs (heteros = other).
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PHOTOSYNTHESIS — FOOD MAKING PROCESS IN PLANTS
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Leaves are the food factories of plants. The synthesis of food in plants occurs in leaves.
All the raw materials must reach there.
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Water and minerals present in the soil are absorbed by the roots and transported to the leaves.
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Water and minerals are transported to the leaves by the vessels which run like pipes throughout the root, the stem,
the branches and the leaves.
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They form a continuous path or passage for the nutrients to reach the leaf.
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Carbon dioxide from air is taken in through the tiny pores present on the surface of the leaves.
These pores are surrounded by ‘guard cells’. Such pores are called stomata.
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PHOTOSYNTHESIS
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The leaves have a green pigment 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.
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Since the synthesis of food occurs in the presence of sunlight, it is called photosynthesis(Photo: light; synthesis : to combine).
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The solar energy is captured by the leaves and stored in the plant in the form of food. Thus, sun is
the ultimate source of energy for all living organisms.
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Oxygen which is essential for the survival of all living organisms is produced during photosynthesis.
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In the absence of photosynthesis, life would be impossible on the earth.
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During photosynthesis, chlorophyll containing cells of leaves, in the presence of sunlight, use carbon dioxide and water to synthesise carbohydrates.
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Carbon dioxide + water —–sunlight—chlorophyll– > Carbohydrate + oxygen
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The carbohydrates ultimately get converted into starch. The starch is also a carbohydrate.
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The leaves other than green also have chlorophyll. The large amount of red, brown and other pigments mask the
green colour. Photosynthesis takes place in these leaves also.
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Besides leaves, photosynthesis also takes place in other green parts of the plant — in green stems and green branches. The desert plants have scale- or spine-like leaves to reduce loss of water by transpiration. These plants have green stems which carry out photosynthesis.
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Slimy, green patches in ponds or in other stagnant water bodies are generally formed by the growth of organisms called algae. Algae are green in colour. They contain chlorophyll which gives them the green colour. Algae can also prepare their own food by photosynthesis.
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Synthesis of plant food other than carbohydrates
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The carbohydrates are made of carbon, hydrogen and oxygen. These are used to synthesise other components of food.
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Proteins are nitrogenous substances which contain nitrogen.
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Nitrogen is present in abundance in gaseous form in the air.
Plants cannot absorb nitrogen in this form.
Soil has certain bacteria that convert gaseous nitrogen into a usable form and release it into the soil.
These soluble forms are absorbed by the plants along with water. Farmers also add fertilisers rich in nitrogen to the soil.
In this way Plants can then synthesise components of food other than carbohydrates such as proteins and fats.
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[Short Notes – E&B] NCERT Class VII – Science – Nutrition in Plants – Chapter 1- Part 2
