Science Chapter-1 (Nutrition In plants) Class 7 Notes

 NUTRIENTS: -

• 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. Human and animal are directly or indirectly dependent on plants. Humans and animals are directly or indirectly dependent on plants.

MODE OF NUTRITIION 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 by body.

• The mode of nutrition in which organisms make food themselves from simple substances is called autotrophic (auto = self; trophos = nourishment) nutrition are called autotrophs. 

• 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. 

• 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 leaves. These pores are surrounded by ‘guard cells. Such pores are called stomata.

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  Water and minerals are transported to the leaves by the vessels which run like pipes throughout the root, the stem. They form a continuous path or passage for the nutrients to reach the leaf. They are called vessels. 

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  The leaves have a green pigment called chlorophyll It helps leaves to capture the energy of the sunlight. This energy is used to synthesize (prepare) food from carbon dioxide and water. Since the synthesis of food occurs in the presence of sunlight, it is called photosynthesis. Photosynthesis also can be displayed in an equation (Photo: light; synthesis: to combine). 
  

• 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.

• 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. 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. The presence of starch in leaves indicates the occurrence of photosynthesis. Starch is also a carbohydrate.
  
  
  

• You see slimy, green patches in ponds or stagnant water bodies. These are generally formed by the growth of organisms called algae. They contain chlorophyll which gives them the green color. Algae can also prepare their own food by photosynthesis.

Cells: -

• The bodies of living organisms are made of tiny units called cells. Cells can be seen only under the microscope.

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

THE DESERT PLANTS: -

• 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.

Synthesis of plant food other than carbohydrates

• Carbohydrates are made of carbon, hydrogen and oxygen.

• 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.

• Also, you might have seen farmers adding fertilizers rich in nitrogen to the soil. In this way the plants fulfil their requirements of nitrogen along with the other constituents.

Other Mode Of Nutrition:

• Like humans and animals such plants depend on the food produced by other plants. They use the heterotrophic mode of nutrition.

• The yellow wiry branched structure twining around the stem and branches, this plant is known as 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. Cuscuta is called the parasite.

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  The pitcher-like or jug-like structure is the modified part of 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.

• These organisms are called fungi. They have a different mode of nutrition. 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, The fungal spores are generally present in the air.

• Some organisms live together and share both shelter and nutrients. This relationship is called symbiosis. For example, certain fungi live inside the roots of plants. The plants provide nutrients to the fungus, and, in return, the fungus provides water and certain nutrients.

• 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 prepares and provides food to the fungus.

HOW NUTRIENTS ARE REPLENISHED IN THE SOIL

• So, their amounts in the soil keep on declining. Fertilizers 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. 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. 

• Most of the plants are autotrophs. Only a few plants are parasitic or saprotrophic. They derive nutrition, from other organisms. All animals are categorized as heterotrophs since they depend on plants and other animals for food.