CLASS VII – SCIENCE��CHAPTER -1�NUTRITION IN PLANTS

The food enable living organisms to:

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• build their bodies,
• to grow,
• to repair damaged parts of their bodies and
• provide the energy to carry out life processes

WHY DO WE NEED FOOD?

Definition:

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Carbohydrates, proteins, fats, vitamins and minerals are components of food. These components of food are necessary for our body and are called nutrients.

NUTRIENTS

Definition:

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Nutrition is the mode of taking food by an organism and its utilization by the body.

NUTRITION

DIFFERENT MODES OF NUTRITION

AUTOTROPH

HETEROTROPH

MODES OF NUTRITION

SYMBIOTIC RELATIONSHIP

INSECTIVOROUS PLANTS

PARASITE

SAPROTROPHS

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.

AUTOTROPES

GREEN PLANTS

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

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HETEROTROPES

ANIMALS

The 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.

SAPROTROPH

• There are some plants which do not have chlorophyll.
• They cannot synthesis their food.
• such plants depend on the food produced by other plants.
• They use the heterotrophic mode of nutrition.
• It does not have chlorophyll in it.
• It takes ready made food from the plant 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.

PARASITES

CUSCUTA

• There are a few plants which can trap insects and digest them.
• Such insect-eating plants are called insectivorous plants.
• Such plants do not get all the required nutrients from the soil in which they grow.

INSECTIVOROUS PLANTS

SOME INSECTIVOROUS PLANTS

PITCHER PLANT

VENUS FLY TRAP

SUN DEW

• 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.

SYMBIOTIC RELATIONSHIP

• 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 association is of great significance for the farmers.

SYMBIOTIC RELATIONSHIP

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

CELL STRUCTURE

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• 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.
• 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.

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PHOTOSYNTHESIS

1. STOMATA

2.CHLOROPHYLL PIGMENT

• 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 (Photo: light; synthesis : to combine).
• 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

DIAGRAM SHOWING PHOTOSYNTHESIS

EQUATION FOR PHOTOSYNTHESIS:

• 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 as an equation:

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Carbon dioxide + water (in the presence of sun light and chlorophyll pigment) Carbohydrate oxygen

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CO2+H2O SUNLIGHT C6H12O6+O2+H2O

CHLOROPHYLL

LEAFS OF VARIOUS COLOURS.

The leaves other than green also have chlorophyll. The large amount of red, brown and other pigments mask the green colour Photosynthesis takes place in these leaves also.

ALGAE DO PHOTOSYNTHESIS.

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.

HOW NUTRIENTS ARE

REPLENISHED IN THE SOIL

• Spreading manure or fertilizers in the fields,

( Fertilizers 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.

• Growing leguminous plant,

(that can fix atmospheric nitrogen with the help of rhizobium bacteria).

• Mixed cropping,
• Crop rotation,
• Field fellow
• Making compost,
• Vermicomposting.

TESTING THE PRESENCE OF STARCH

• Take a potted plant with broad leaves.
• Take two strips of black paper and cut out a small square in their centers.
• Cover a part of two leaves with these papers and secure them with paper clips .
• 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.

QUESTION 1

QUESTION 2

QUESTION 3

SUMMARY

• All organisms take food and utilize it to get energy for the growth and maintenance of their bodies.
• Green plants synthesize 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 utilized 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.