n 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 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.
Nutrition in Plants
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 autotrophs. and most other organisms take in ready made food prepared by the plants. They are called heterotrophs (heteros = other).
Paheli wants to know why our body cannot make food from carbon dioxide, water and minerals like plants do. 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?
Boojho wants to know how plants prepare their own food.
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
1 .2 PHOTOSYNTHESIS — FOOD MAKING PROCESS IN PLANTS
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
You have seen that buildings are made of bricks. Similarly, the bodies of living organisms are made of tiny units called cells Cells can be seen cells. only under the microscope. Some organisms are made of only one cell. The cell is enclosed by a thin outer boundary, called the cell membrane membrane. Most cells have a distinct, centrally located spherical structure called the nucleus (Fig. 1.1). The nucleus is surrounded by a jelly-like substance called cytoplasm cytoplasm. leaves. 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 [Fig. 1.2 (c)]. Boojho wants to know how water and minerals absorbed by roots reach the leaves. 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. Nucleus
Cytoplasm Cell membrane
Fig. 1.1 Cell
Paheli wants to know what is so special about the leaves that they can synthesise food but other parts of the plant cannot.
The leaves have a green pigment called chlorophyll It helps leaves to chlorophyll. 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 of 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 earth . 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 organisms. living organisms Can you imagine the earth in the absence of photosynthesis!...
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