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NCERT Class VII Science Chapter 1 Nutrition in Plants

National Council of Educational Research and Training (NCERT) Book for Class VII
Subject: Science
Chapter: Chapter 1 – Nutrition in Plants

Class VII NCERT Science Text Book Chapter 1 Nutrition in Plants is given below

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

Cells

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 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. 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.

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)].

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 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 living organisms.

Can you imagine the earth in the absence of photosynthesis!

In the absence of photosynthesis there would not be any plants. The survival of almost all living organisms directly or indirectly depends upon the   food made by the plants. Besides,oxygen which is essential for the survival

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 during  photosynthesis. In the absence of  photosynthesis, life would be impossible on the earth.

During photosynthesis, chlorophyll containing  cells of leaves (Fig. 1.2), in the presence of  sunlight, use carbon dioxide and water to  synthesise carbohydrates (Fig. 1.3). The process
can be represented as an equation:

Carbon dioxide water

Carbohydrate oxygen

 

 

 

 

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.

Activity 1.1

Take two potted plants of the same kind. Keep one in the dark (or in a black box)for 72 hours and the other in  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.

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

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 for 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

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 getsentangled into the hair. The insect is  digested  by the digestive juices secreted in the pitcher.  Such insect-eating plants are called  insectivorous plants. 

Is it possible that such  plants do not get all the required nutrients  from the soil in which they grow?

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 they need  to survive and from where they get them.

Activity 1.2

Take a piece of bread and moisten it with water. Leave it in a moist warm place for 2–3  days or until fluffy patches appear on them  (Fig. 1.8). These patches may be white, green,  brown or of any other colour. Observe the  patches under a microscope or a magnifying glass.

Write down your observations in your notebook. Most probably you will see cotton- like threads spread on the piece of bread.

These organisms are called fungi. They have  a different mode of nutrition.They secrete  digestive juices on the dead and decaying  matter and convert it into a solution. Then  they absorb the nutrients from it. This mode  of nutrition in which organisms take in  nutrients in solution form from dead and  decaying matter is called saprotrophic  nutrition. Plants which use saprotrophic mode of nutrition are called saprotrophs.

Fungi also grow on pickles, leather, clothes  and other articles that are left in hot and  humid weather for long time.

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 find out the nutrient  requirement of plants. Usually crops require a  lot of nitrogen to make proteins. After the  harvest, the soil becomes deficient in nitrogen.  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  have a symbiotic relationship. This  associationis 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 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?

Keywords

Autotrophic Insectivorous Photosynthesis
Chlorophyll Nutrient Saprotrophs
Heterotrophs Nutrition Saprotrophic
Host Parasite Stomata

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 by the leaves with the help of chlorophyll.
  • Oxygen is produced during photosynthesis.
  • Oxygen released in photosynthesis is utilised by other 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.

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) A plant 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)

(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 gets carbon dioxide from the air for photosynthesis.

(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:

(i) roots (ii) stem (iii) flowers (iv) leaves

Extended Learning — Activities and Projects

1. Project

Take a potted plant with broad leaves. Take two strips of black paper and cut out a small square in their centres.   Cover a part of two leaves with these papers and secure them with paper clips (Fig. 1.9). 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. Perform iodine test on this leaf. Did the two parts show any difference  in results? Now take another   leaf. 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 light, water and carbon dioxide.

3. Try growing a sweet potato just in water. Describe your experiment and observations.

You can read more on the following website:

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.

Go to NCERT Class VII Science Book Home Page All NCERT Books

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