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. 1.1 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? 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 sunlight. Perform iodine test with the leaves of both the plants as you did in Class VI. Record your results. Now leave the pot which was earlier kept in the dark, in the sunlight for 3 – 4 days and perform the iodine test again on its leaves. Record your observations in your notebook. The leaves other than green also have chlorophyll. The large amount of red, brown and other pigments mask the green colour (Fig. 1.4). Photosynthesis takes place in these leaves also. You often see slimy, green patches in ponds or in other stagnant water bodies. These are generally formed by the growth of organisms called algae. Can you guess why algae are green in colour? They contain chlorophyll which gives them the green colour. Algae can also prepare their own food by photosynthesis. Synthesis of plant food other than carbohydrates You have just learnt that plants synthesise carbohydrates through the process of photosynthesis. The carbohydrates are made of carbon, hydrogen and oxygen. These are used to synthesise other components of food such as proteins and fats. But proteins are nitrogenous substances which contain nitrogen. From where do the plants obtain nitrogen? Recall that nitrogen is present in abundance in gaseous form in the air. However, 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. Also, you might have seen farmers adding fertilisers rich in nitrogen to the soil. In this way the plants fulfil their requirements of nitrogen along with the other constituents. Plants can then synthesise components of food other than carbohydrates such as proteins and fats. 1.3 OTHER MODES OF NUTRITION IN PLANTS There are some plants which do not have chlorophyll. They cannot synthesise their food. How do they survive and from where do they derive nutrition? Like humans and animals such plants depend on the food produced by other plants. They use the heterotrophic mode of nutrition. Look at Fig. 1.5. Do you see yellow tubular structures twining around the stem and branches of a tree? This is a plant called Cuscuta (Amarbel). It does not have chlorophyll. It takes readymade food from the plant SCIENCE on which it is climbing. The plant on which it climbs is called a host. Since it deprives the host of valuable nutrients, it is called a parasite. Are we and the other animals also parasites on the plants? You should think about it and discuss with your teacher. Have you seen or heard of plants that can eat animals? There are a few plants which can trap insects and digest them. Is it not amazing? Such plants may be green or of some other colour. Look at the plant in Fig. 1.6. The pitcher-like NUTRITION IN PLANTS Boojho says once his grandfather told him that his wheat fields were spoiled by a fungus. He wants to know if fungi cause diseases also. Paheli told him that many fungi like yeast and mushrooms are useful, but some fungi cause diseases in plants, animals and humans. Some fungi are also used in medicines. During the rainy season they spoil many things. Ask your parents about the menace of fungi in your house. The fungal spores are generally present in the air. When they land on wet and warm things they germinate and grow. Now, can you figure out how we can protect our things from getting spoiled? Some organisms live together and share shelter and nutrients. This is called symbiotic relationship. For example, certain fungi live in the roots of trees. The tree provides nutrients to the fungus and, in return, receives help from it to take up water and nutrients from the soil. This association is very important for the tree. In organisms called lichens, a chlorophyll-containing partner, which is an alga, and a fungus live together. The fungus provides shelter, water and minerals to the alga and, in return, the alga provides food which it prepares by photosynthesis. 1.5 HOW NUTRIENTS ARE REPLENISHED IN THE SOIL Have you seen farmers spreading manure or fertilisers in the fields, or gardeners using them in lawns or in pots? Do you know why they are added to the soil? You learnt that plants absorb mineral nutrients from the soil. So, their amounts in the soil keep on declining. Fertilisers and manures contain plant nutrients such as nitrogen, potassium, phosphorous, etc. These nutrients need to be added from time to time to enrich the soil. We can grow plants and keep them healthy if we can fulfil the nutrient requirement of plants. Usually crops require a lot of nitrogen to make proteins. After the harvest, the soil becomes deficient in nitrogen. You learnt that though nitrogen gas is available in plenty in the air, plants cannot use it in the manner they can use carbon dioxide. They need nitrogen in a soluble form. The bacterium called Rhizobium can take atmospheric nitrogen and convert it into a soluble form. But Rhizobium cannot make its own food. So it lives in the roots of gram, peas, moong, beans and other legumes and provides them with nitrogen. Most of the pulses (dals) are obtained from leguminous plants. In return, the plants provide food and shelter to the bacteria. They, thus, have NUTRITION IN PLANTS symbiotic relationship. This association is of great significance for the farmers. They do not need to add nitrogen fertiliser to the soil in which leguminous plants are grown. In this chapter you learnt that most of the plants are autotrophs. Only a few plants adopt other modes Keywords What you have learnt • All organisms take food and utilise it to get energy for the growth and maintenance of their bodies. • Green plants synthesise their food themselves by the process of photosynthesis. They are autotrophs. • Plants use simple chemical substances like carbon dioxide, water and minerals for the synthesis of food. • Chlorophyll and sunlight are the essential requirements for photosynthesis. • Complex chemical substances such as carbohydrates are the products of photosynthesis. • Solar energy is stored in the form of food in the leaves with the help of chlorophyll. • Oxygen is produced during photosynthesis. • Oxygen released in photosynthesis is utilised by living organisms for their survival. • Fungi derive nutrition from dead, decaying matter. They are saprotrophs. Plants like Cuscuta are parasites. They take food from the host plant. • A few plants and all animals are dependent on others for their nutrition and are called heterotrophs. of nutrition like parasitic and saprotrophic. They derive nutrition from other organisms. All animals are categorised as heterotrophs since they depend on plants and other animals for food. Can we say that the insectivorous plants are partial heterotrophs? SCIENCE Insectivorous Nutrient Nutrition Parasite Exercise 1. Why do organisms need to take food? 2. Distinguish between a parasite and a saprotroph. 3. How would you test the presence of starch in leaves? 4. Give a brief description of the process of synthesis of food in green plants. 5. Show with the help of a sketch that the plants are the ultimate source of food. 6. Fill in the blanks: (a) Green plants are called _________________ since they synthesise their own food. (b) The food synthesised by the plants is stored as _________________. (c) In photosynthesis solar energy is captured by the pigment called ___________. (d) During photosynthesis plants take in ______________________ and release __________________. 7. Name the following: (i) A parasitic plant with yellow, slender and tubular stem. (ii) Aplant that has both autotrophic and heterotrophic mode of nutrition. (iii) The pores through which leaves exchange gases. 8. Tick the correct answer: (a) Amarbel is an example of: (i) autotroph (ii) parasite (iii) saprotroph (iv) host (b) The plant which traps and feeds on insects is: (i) Cuscuta (ii) china rose (iv) pitcher plant (iv) rose 9. Match the items given in Column I with those in Column II: Column I Column II Chlorophyll Bacteria Nitrogen Heterotrophs Amarbel Pitcher plant Animals Leaf Insects Parasite 10. Mark ‘T’ if the statement is true and ‘F’ if it is false: (i) Carbon dioxide is released during photosynthesis. (T/F) NUTRITION IN PLANTS

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