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1 Nutrition in Plants I n Class VI you learnt that food is utilisation by the body. The mode of essential for all living organisms. nutrition in which organisms make food You also learnt that carbohydrates, themselves from simple substances is...

1 Nutrition in Plants I n Class VI you learnt that food is utilisation by the body. The mode of essential for all living organisms. nutrition in which organisms make food You also learnt that carbohydrates, themselves from simple substances is ed proteins, fats, vitamins and minerals are called autotrophic (auto = self; trophos components of food. These components = nourishment) nutrition. Therefore, of food are necessary for our body and plants are called autotrophs. Animals h are called nutrients. and most other organisms take in ready pu T All living organisms require food. made food prepared by the plants. They is Plants can make their food themselves re ER are called heterotrophs (heteros = but animals including humans cannot. other). bl They get it from plants or animals that eat plants. Thus, humans and animals are directly or indirectly dependent on Paheli wants to know why be C plants. our body cannot make food from carbon dioxide, water and minerals like plants do. N Boojho wants to know how plants prepare Now we may ask where the food to © their own food. factories of plants are located: whether food is made in all parts of a plant or only in certain parts? How do plants 1.1 MODE OF NUTRITION IN PLANTS obtain the raw materials from the Plants are the only organisms that can surroundings? How do they transport prepare food for themselves by using them to the food factories of the plants? water, carbon dioxide and minerals. The raw materials are present in their 1.2 PHOTOSYNTHESIS — FOOD surroundings. MAKING PROCESS IN PLANTS t The nutrients enable living Leaves are the food factories of plants. no organisms to build their bodies, to grow, The synthesis of food in plants occurs to repair damaged parts of their bodies in leaves. Therefore, all the raw and provide the energy to carry out life materials must reach there. Water and processes. Nutrition is the mode of minerals present in the soil are absorbed taking food by an organism and its by the roots and transported to the  Cells You have seen that buildings are made of bricks. Nucleus Similarly, the bodies of living organisms are made of tiny units called cells. Cells can be seen only under the microscope. Some organisms are made of only one cell. The cell is enclosed by Cytoplasm a thin outer boundary, called the cell membrane. ed Most cells have a distinct, centrally located Cell membrane spherical structure called the nucleus (Fig. 1.1). The nucleus is surrounded by a jelly-like substance called cytoplasm. h Fig. 1.1 Cell pu T is leaves. Carbon dioxide from air is taken re ER The leaves have a green pigment in through the tiny pores present on the called chlorophyll. It helps leaves to surface of the leaves. These pores are bl capture the energy of the sunlight. This surrounded by ‘guard cells’. Such pores energy is used to synthesise (prepare) are called stomata [Fig. 1.2 (c)]. food from carbon dioxide and water. Since the synthesis of food occurs in the be C presence of sunlight, it is called Boojho wants to know how water photosynthesis (Photo: light; synthesis : N and minerals absorbed by roots to combine). So we find that chlorophyll, reach the leaves. sunlight, carbon dioxide and water are necessary to carry out the process of to © Water and minerals are transported photosynthesis. It is a unique process to the leaves by the vessels which run on the earth. The solar energy is like pipes throughout the root, the stem, captured by the leaves and stored in the the branches and the leaves. They form plant in the form of food. Thus, sun is a continuous path or passage for the the ultimate source of energy for all nutrients to reach the leaf. You will learn living organisms. about transport of materials in plants Can you imagine life on earth in the in Chapter 11. absence of photosynthesis! t In the absence of photosynthesis no there would not be any food. The Paheli wants to know what is so survival of almost all living organisms special about the leaves that they directly or indirectly depends upon the can synthesise food but other food made by the plants. Besides, parts of the plant cannot. oxygen which is essential for the survival 2 SCIENCE  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. of all living organisms is produced Light energy during photosynthesis. In the absence of photosynthesis, life would be ed impossible on the earth. During photosynthesis, chlorophyll Carbon containing cells of leaves (Fig. 1.2), in dioxide the presence of sunlight, use carbon Chlorophyll h Oxygen in leaf dioxide and water to synthesise pu T is carbohydrates (Fig. 1.3). The process re ER can be represented as an equation: Water and bl sunlight Carbon dioxide + water ⎯⎯⎯⎯⎯⎯ chlorophyll → minerals Carbohydrate + oxygen Fig. 1.3 Diagram showing photosynthesis be C Chlorophyll During the process oxygen is released. The carbohydrates ultimately N get converted into starch. The presence of starch in leaves indicates the occurrence of photosynthesis. The to © starch is also a carbohydrate. Guard cells Stoma Boojho has observed some (b) A section through a leaf plants with deep red, violet or Guard cells brown leaves. He wants to know whether these leaves (a) Leaf also carry out photosynthesis. t no Activity 1.1 Stomatal opening Take two potted plants of the same kind. (c) Stomata Keep one in the dark (or in a black box) Fig. 1.2 for 72 hours and the other in the NUTRITION IN PLANTS 3 sunlight. Perform iodine test with the process of photosynthesis. The leaves of both the plants as you did in carbohydrates are made of carbon, Class VI. Record your results. Now leave hydrogen and oxygen. These are used the pot which was earlier kept in the to synthesise other components of food dark, in the sunlight for 3 – 4 days and such as proteins and fats. But proteins perform the iodine test again on its are nitrogenous substances which leaves. Record your observations in your contain nitrogen. From where do the notebook. plants obtain nitrogen? The leaves other than green also have Recall that nitrogen is present in ed chlorophyll. The large amount of red, abundance in gaseous form in the air. brown and other pigments mask the However, plants cannot absorb nitrogen green colour (Fig. 1.4). Photosynthesis in this form. Soil has certain bacteria that h takes place in these leaves also. convert gaseous nitrogen into a usable pu T form and release it into the soil. These is soluble forms are absorbed by the plants re ER along with water. Also, you might have bl seen farmers adding fertilisers rich in nitrogen to the soil. In this way the plants fulfil their requirements of be C nitrogen along with the other constituents. Plants can then synthesise N components of food other than carbohydrates such as proteins and fats. Fig. 1.4 Leaves of various colours 1.3 OTHER MODES NUTRITION to © OF IN You often see slimy, green patches PLANTS in ponds or in other stagnant water There are some plants which do not have bodies. These are generally formed by chlorophyll. They cannot synthesise the growth of organisms called algae. their food. How do they survive and from Can you guess why algae are green in where do they derive nutrition? Like colour? They contain chlorophyll which humans and animals such plants gives them the green colour. Algae can depend on the food produced by other also prepare their own food by plants. They use the heterotrophic t no photosynthesis. mode of nutrition. Look at Fig. 1.5. Do you see yellow tubular structures Synthesis of plant food other twining around the stem and branches than carbohydrates of a tree? This is a plant called Cuscuta You have just lear nt that plants (Amarbel). It does not have chlorophyll. synthesise carbohydrates through the It takes readymade food from the plant 4 SCIENCE  structure is the modified part of the leaf. The apex of the leaf forms a lid which can open and close the mouth of the pitcher. Inside the pitcher there are hair which are directed downwards. When an insect lands in the pitcher, the lid closes and the trapped insect gets entangled into the hair. The insect is digested by the digestive juices secreted ed in the pitcher. Such insect-eating plants are called insectivorous plants. Is it possible that such plants do not h get all the required nutrients from the pu T soil in which they grow? is re ER Fig. 1.5 Cuscuta (Amarbel) on host plant bl on which it is climbing. The plant on which it climbs is called a host. Since it Boojho is confused. If the deprives the host of valuable nutrients, pitcher plant is green and be C it is called a parasite. Are we and the carries out photosynthesis, then other animals also parasites on the why does it feed on insects? N plants? You should think about it and discuss with your teacher. to © Lid Paheli wants to know whether mosquitoes, bed bugs, lice and leeches that suck our blood are also parasites. t Have you seen or heard of plants that no can eat animals? There are a few plants which can trap insects and digest them. Is it not amazing? Such plants may be Leaf modified into pitcher green or of some other colour. Look at the plant in Fig. 1.6. The pitcher-like Fig. 1.6 Pitcher plant showing lid and pitcher NUTRITION IN PLANTS 5 1.4 SAPROTROPHS You might have seen packets of mushrooms sold in the vegetable market. You may have also seen fluffy umbrella-like patches growing on rotting wood during the rainy season (Fig. 1.7). Let us find out what type of nutrients Fig. 1.8 Fungi they need to survive and from where growing on bread ed they get them. Write down your observations in your notebook. Most probably you will see h cotton-like threads spread on the piece pu T of bread. is re ER These organisms are called fungi. They have a different mode of nutrition. bl They secrete digestive juices on the dead Fig. 1.7 Packet of mushrooms, a mushroom and decaying matter and convert it into growing on decayed material a solution. Then they absorb the be C nutrients from it. This mode of nutrition in which organisms take in nutrients in solution form from dead and decaying N Boojho wants to know how matter is called saprotrophic nutrition. these organisms acquire Plants which use saprotrophic mode of nutrients. They do not have nutrition are called saprotrophs. to © mouths like animals do. They are Fungi also grow on pickles, leather, not like green plants as they lack clothes and other articles that are left chlorophyll and cannot make food in hot and humid weather for long time. by photosynthesis. Activity 1.2 Paheli is keen to know whether her beautiful shoes, Take a piece of bread and moisten it with t which she wore on special water. Leave it in a moist warm place no occasions, were spoiled by fungi for 2–3 days or until fluffy patches during the rainy season. She appear on them (Fig. 1.8). These patches wants to know how fungi appear may be white, green, brown or of any suddenly during the rainy other colour. Observe the patches under season. a microscope or a magnifying glass. 6 SCIENCE  fungus provides shelter, water and minerals to the alga and, in return, the alga provides food which it prepares by Boojho says once his photosynthesis. grandfather told him that his wheat fields were spoiled by a 1.5 HOW NUTRIENTS ARE fungus. He wants to know if REPLENISHED IN THE SOIL fungi cause diseases also. Have you seen farmers spreading manure or fertilisers in the fields, or ed Paheli told him that many fungi gardeners using them in lawns or in like yeast and mushrooms are pots? Do you know why they are added useful, but some fungi to the soil? cause diseases in plants, h You learnt that plants absorb animals and humans. pu T mineral nutrients from the soil. So, their is Some fungi are also used re ER amounts in the soil keep on declining. in medicines. Fertilisers and manures contain plant bl nutrients such as nitrogen, potassium, phosphorous, etc. These nutrients need During the rainy season they spoil many to be added from time to time to enrich be C things. Ask your parents about the the soil. We can grow plants and keep menace of fungi in your house. them healthy if we can fulfil the nutrient N The fungal spores are generally requirement of plants. present in the air. When they land on Usually crops require a lot of nitrogen wet and warm things they germinate to make proteins. After the harvest, the to © and grow. Now, can you figure out how soil becomes deficient in nitrogen. You we can protect our things from getting learnt that though nitrogen gas is available spoiled? in plenty in the air, plants cannot use it Some organisms live together and in the manner they can use carbon share shelter and nutrients. This is dioxide. They need nitrogen in a soluble called symbiotic relationship. For form. The bacterium called Rhizobium can example, certain fungi live in the roots take atmospheric nitrogen and convert it of trees. The tree provides nutrients to into a soluble form. But Rhizobium cannot the fungus and, in return, receives help make its own food. So it lives in the roots t no from it to take up water and nutrients of gram, peas, moong, beans and other from the soil. This association is very legumes and provides them with important for the tree. nitrogen. Most of the pulses (dals) are In organisms called lichens, a obtained from leguminous plants. In chlorophyll-containing partner, which is return, the plants provide food and an alga, and a fungus live together. The shelter to the bacteria. They, thus, have NUTRITION IN PLANTS 7 a symbiotic relationship. This of nutrition like parasitic and association is of great significance for saprotrophic. They derive nutrition the farmers. They do not need to add from other organisms. All animals nitrogen fertiliser to the soil in which are categorised as heterotrophs since leguminous plants are grown. they depend on plants and other In this chapter you learnt that animals for food. Can we say that most of the plants are autotrophs. the insectivorous plants are partial Only a few plants adopt other modes heterotrophs? ed Keywords h Autotrophic Insectivorous Photosynthesis pu T is Chlorophyll re ER Nutrient Saprotrophs Heterotrophs Nutrition Saprotrophic bl Host Parasite Stomata be C What you have learnt N „ 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 to © 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. t „ Oxygen released in photosynthesis is utilised by living organisms for no 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. 8 SCIENCE  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. ed 6. Fill in the blanks: (a) Green plants are called _________________ since they synthesise their own food. h (b) The food synthesised by the plants is stored as _________________. pu T is (c) In photosynthesis solar energy is captured by the pigment called ___________. re ER (d) During photosynthesis plants take in ______________________ and bl release __________________. 7. Name the following: (i) A parasitic plant with yellow, slender and tubular stem. be C (ii) A plant that has both autotrophic and heterotrophic mode of nutrition. (iii) The pores through which leaves exchange gases. N 8. Tick the correct answer: (a) Amarbel is an example of: to © (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 t no 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 9  (ii) Plants which synthesise their food themselves are called saprotrophs. (T/F) (iii) The product of photosynthesis is not a protein. (T/F) (iv) Solar energy is converted into chemical energy during photosynthesis. (T/F) 11. Choose the correct option from the following: Which part of the plant takes in carbon dioxide from the air for photosynthesis? ed (i) Root hair (ii) Stomata (iii) Leaf veins (iv) Sepals 12. Choose the correct option from the following: Plants take carbon dioxide from the atmosphere mainly through their: h (i) roots (ii) stem (iii) flowers (iv) leaves pu T is Extended Learning — Activities and Projects re ER 1. Project bl Take a potted plant with broad leaves. Take two strips of black paper and cut out a small square be C in their centres. Cover a part of two leaves with these papers and secure them with paper clips (Fig. 1.9). N Keep the plant in the sunlight for 2–5 days. Observe the difference in the colour of the covered and the uncovered portions on the one leaf. to © Perform iodine test on this leaf. Did the two parts show any difference Fig. 1.9 Experiment to test the in results? Now take second leaf. occurrence of photosynthesis Remove the strip and expose the covered part to the sunlight for 2– 3 days and do the iodine test again. Describe your observations. 2. Visit a green house if there is one near your place. Observe how they raise plants. Find out how they regulate the amount of light, water and carbon dioxide to grow the plants. 3. Try growing a sweet potato just in water. Describe your experiment and observations. t You can read more on the following website: no www.phschool.com/science/biology_place/biocoach/photosynth/ overview.htm Did you know? Light is so important to plants that their leaves grow in many patterns so as to catch the most sunlight. 10 SCIENCE