Nutrition in Plants-NCERT

 

Nutrition in Plants

Food is essential for all living organisms and carbohydrates, proteins, fats, vitamins, and minerals are components of food. These components of food are called nutrients and are necessary for our body.

All living organisms require food. Plants can synthesize food for 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 nutrition. Therefore, plants are called autotrophs

( auto=self; trophos=nourishment)

 Animals and most other organisms take in food prepared by plants. They are called heterotrophs (heteros=other).

Photosynthesis — Food Making Process in Plants

Leaves are the food factories of plants. Therefore, all the raw materials must reach the leaf. Water and minerals present in the soil are absorbed by the roots and transported to the leaves. Carbon dioxide from the air is taken in through the tiny pores present on the surface of leaves. These pores are surrounded by ‘guard cells’. Such pores are called stomata.

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. They are called vessels.

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, the sun is the ultimate source of energy for all living organisms.

 

In the absence of photosynthesis, there would not be any food. 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 of all organisms, is produced during photosynthesis. In the absence of photosynthesis, life would be impossible on the earth.

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

 

Carbon dioxide + water         sunlight →chlorophyl     Carbohydrate + oxygen

 

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 the loss of water by transpiration. These plants have green stems which carry out photosynthesis.

 

Synthesis of Plant Food Other Than Carbohydrates

Plants synthesize 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.

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 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 proteins and vitamins.

 

Other Modes of Nutrition in Plants

There are some plants which do not have chlorophyll. They cannot synthesise 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. 

Do you see a yellow wiry branched structure 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 the host. Since it deprives the host of valuable nutrients, Cuscuta is called the parasite.

There are a few plants which can trap insects and digest them. Such plants may be green or of some other colour. The pitcher-like or jug-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 gets entangled into the hair. The lid closes and the insect is trapped. The insect is digested by the digestive juices secreted in the pitcher, and its nutrients are absorbed. Such insect-eating plants are called insectivorous plants.

 

Saprotrophs

You might have seen packets of mushrooms sold in the vegetable market. You may have also seen fluffy umbrella-like patches growing in moist soils or on rotting wood during the rainy season. Let us find out what type of nutrients they need to survive and from where they get them.

These organisms are called fungi. They have a different mode of nutrition. They absorb the nutrients from the bread. This mode of nutrition in which organisms take in nutrients from dead and decaying matter is called saprotrophic nutrition. Such organisms with 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 a 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.

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 this is done?

You learnt that plants absorb minerals and nutrients from the soil. So, their amounts in the soil keep on declining. Fertilisers and manures contain 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, crop plants absorb a lot of nitrogen, and 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 usable form. But Rhizobium cannot make its own food. So it often lives in the roots of gram, peas, moong, beans, and other legumes and provides them with nitrogen. In return, the plants provide food and shelter to the bacteria. They, thus, have a symbiotic relationship. This association is of great significance for the farmers. They can reduce the use of nitrogenous fertiliser where leguminous plants are grown. Most of the pulses (dals) are obtained from leguminous plants.

In this chapter, you learnt that most of the plants are autotrophs. Only a few plants are parasitic or 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?

---

What You Have Learnt

• All organisms need food and utilise it to get energy for growth and maintenance of their body.
• Green plants synthesise food for themselves by the process of photosynthesis. They are autotrophs.
• Plants like Cuscuta are parasites. They take food from the host plant.
• Plants use simple chemical substances like carbon dioxide, water, and minerals for the synthesis of food.
• Chlorophyll, water, carbon dioxide, and sunlight are the essential requirements for photosynthesis.
• Complex chemical substances such as carbohydrates are the products of photosynthesis.
• Solar energy is absorbed by the chlorophylls present in leaves/plants.
• Oxygen is produced during photosynthesis.
• Oxygen released in photosynthesis is utilised by living organisms for their survival.
• Many fungi derive nutrition from dead and decaying matter. They are saprotrophs.
• A few plants and all animals are dependent on others for their nutrition and are called heterotrophs.

---

Exercise

1.    Why do organisms 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.    Fill in the blanks:

(a) Green plants are called ______ since they synthesise their own food.
(b) The food synthesised by plants is stored as ______.
(c) In photosynthesis, solar energy is absorbed by the pigment called ______.
(d) During photosynthesis, plants take in ______ and release ______ gas.

6.    Name the following:

(i) A parasitic plant with yellow, slender, and branched stem.
(ii) A plant that is partially autotrophic.
(iii) The pores through which leaves exchange gases.

7.    Tick the correct answer:
(a) Cuscuta 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

8.    Match the items given in Column I with those in Column II:

Column I	Column II
Chlorophyll	Rhizobium
Nitrogen	Heterotrophs
Cuscuta	Pitcher plant
Animals	Leaf
Insects	Parasite

Did you know?

Light is so important to plants that their leaves grow in many patterns so as to absorb maximum sunlight.

 

Based on NCERT, Class-VII