Answer the following questions.
1. How will you determine that the leaves other than green can make their own
food by photosynthesis.
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Objective:
This topic gives you an overview of;
Nutrition in Plants.
Mode of Nutrition in Plants.
Photosynthesis Food Making Process in Plant.
Synthesis of plant food other than carbohydrates.
Other Modes of Nutrition in Plants.
How Nutrients are Replenished in the Soil.
Nutrition in Plants
In Class VI you learnt that food is essential for all living organisms. You also learnt that carbohydrates,proteins, fats, vitamins and minerals are components of food. These components of food are necessary for our body and are called nutrients.
All living organisms require food. Plants can make their food themselves but animals including humans cannot. They get it from plants or animals that eat plants. Thus, humans and animals are directly or indirectly dependent on plants.
Mode of Nutrition in Plants
Plants are the only organisms that can prepare food for themselves by using water, carbon dioxide and minerals. The raw materials are present in their surroundings.
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. Nutrition is the mode of taking food by an organism and its utilisation by the body. The mode of nutrition in which organisms make food themselves from simple substances is called autotrophic (auto = self; trophos = nourishment) nutrition. Therefore, plants are called autotrophs. Animals and most other organisms take in ready made food prepared by the plants. They are called heterotrophs ( heteros = other).
Now we may ask where the food factories of plants are located: whether food is made in all parts of a plant or only in certain parts? How do plants obtain the raw materials from the surroundings? How do they transport them to the food factories of the plants?
Photosynthesis Food Making Process in Plant
Leaves are the food factories of plants. The synthesis of food in plants occurs in leaves. Therefore, all the raw materials must reach there. Water and minerals present in the soil are absorbed by the roots and transported to the leaves. Carbon dioxide from air is taken in through the tiny pores present on the surface of the leaves. These pores are surrounded by stomata [Fig. 1.2 (c)].
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. They form a continuous path or passage for the nutrients to reach the leaf. You will learn about transport of materials in plants in Chapter 11.
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. Since the synthesis of food occurs in the presence o f sunlight , it is called photosynthesis (Photo: light; synthesis : to combine). So we find that chlorophyll, sunlight, carbon dioxide and water are necessary to carry out the process of photosynthesis. It is a unique process on the eart h . The solar energy i s 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.
Can you imagine life on earth in the absence of photosynthesis?
In the absence o f photosynthesis there would not be any food. Th e survival of almost all living organisms directly or indirectly depends upon the food made by the plants. Besi des, oxygen which is essential for the survival of a living organisms is pro du ced during photosynthesis. In the absence o f photosynthesi s, lif e would be impossible on the earth.
During photosynthesis, chlorophyll containing cells of leaves (Fig. 1.2), in the presence of su nlight, use carbon dioxide and water to synthesise carbohydra tes (Fig. 1.3). Th e process can be represented as an equation:
During the process oxygen is released. The carbohydrates ultimately get converted into starch. The presence of starch in leaves indicates the occurrence of photosynthesis. The starch is also a carbohydrate.
Summary
The components of food are necessary for our body and they are called nutrients.
The mode of nutrition in which organisms make food themselves from simple substances is called autotrophic nutrients.
Animals and most other organisms take in ready made food prepared by the plants and are called heterotrophs nutrients.
The leaves have a green pigment called chlorophyll. It helps leaves to capture the energy of the sunlight.