CBSE – 7th Standard Science

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Chapter 1 – Nutrients in plants

 

NUTRIENTS IN PLANTS

  • 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.
  • 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.

autotrophs

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

hetrotrophs

saphrotrophs

  • 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 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
  • 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
  • The nucleus is surrounded by a jelly-like substance called cytoplasm.
  • 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.
  • 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).

photosynthesis

photosynthesis1

  • So we find that chlorophyll, sunlight, carbon dioxide and water are necessary to carry out the process of
  • 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.
  • 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.
  • 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.
  • 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.
  • They contain chlorophyll which gives them the green colour.
  • Algae can also prepare their own food by 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
  • 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.
  • There are some plants which do not have chlorophyll.
  • They cannot synthesise their food.
  • Like humans and animals such plants depend on the food produced by other plants. They use the heterotrophic mode of nutrition. This is a plant called Cuscuta (Amarbel).

deddor

  • It does not have chlorophyll.
  • 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.

rhiz

  • 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.
  • During the rainy season they spoil many things
  • The fungal spores are generally present in the air.
  • When they land on wet and warm things they germinate and grow.
  • Some organisms live together and share shelter and nutrients. This is called symbiotic relationship.
  • 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.

tree and leaves

  • 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.

lichens

  • 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.
  • 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.

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