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Plant Nutrition theory Biology-day-1 Target-ssc-cgl-2018

Plant Nutrition theory Biology-day-1 Target-ssc-cgl-2018

Plant Nutrition theory Biology-day-1 Target-ssc-cgl-2018


Nutrition is the mode of taking food by an organism and its utilization by the body for growth, repair and mechanism. In simple words, it is a process of taking food and utilising it by the organism.

Modes of Nutrition

There are two types of modes of nutrition…

  • Autotrophic (auto = self; trophos =nourishment)
  • Heterotrophic (hetero = other; trophos=nourishment)


Those organisms which make their own food by simple substances by the process known as photosynthesis are called Autotrophs. This mode of nutrition is called autotrophic mode of nutrition.

E.g. All green plants make their food by photosynthesis.


Those organisms which cannot make their own food by the process known as photosynthesis are called Heterotrophs. This mode of nutrition is called heterotrophic mode of nutrition. Heterotrophs depend on autotrophs for nutrition.

E.g. Non-green plants, animals, human being etc.


With the use of simple inorganic substances, plants make their food. These inorganic substances are carbon dioxide and water. This process of making food is known as photosynthesis.

Carbon dioxide  +  Water   → Glucose  +  Oxygen

The plants use carbon dioxide and water in the presence of sunlight and prepare their food in the presence of a green coloured substance called chlorophyll. Chlorophyll is present in the leaves of the plants and gives green colour to them. Plants wanting chlorophyll cannot make their food and thus depends on green plants for nutrition.

The end products of photosynthesis are glucose and oxygen.

Glucose is a simple carbohydrate food.  It later gets converted into more complex carbohydrate called starch. Thus food, in the form of starch, gets stored in different parts of the plants. Since, the synthesis of food occurs in the leaves of the plants, they are also called the food factories of the plants.

Plants make starch, oils, fats, proteins and vitamins as food.

How the plants get CO2 for photosynthesis

Surface of the leaves have tiny pores called stomata which help plants to take carbon dioxide gas from atmosphere. Each stomata is surrounded by a pair of cells called guard cells.

Guard cells surround stomata and controls the opening and the closing of the stomata. These guard cells open up only when either the plant has to take carbon dioxide or the plant has to release oxygen otherwise they remain closed.

How the plants get water for photosynthesis

Water and minerals present in the soil are absorbed by the roots of the plant and transported to its leaves through the interconnected pipe-like xylem vessels present throughout the roots, stems, branches and leaves.

The role of chlorophyll in photosynthesis

Chlorophyll absorbs the light energy from the sun and supplies it to the leaves to enable them to carry out photosynthesis for making food.

The role of sunlight in photosynthesis

It provides energy for making food. The solar energy from the sun gets converted to chemical energy and this chemical energy helps in the preparation of food.


Non-green plants or chlorophyll wanting plants cannot make their own food. They depend on other organisms for nutrition. They are divided into two types…

Parasites :

A plant which lives on or inside other organism and take nutrition from that organism are called parasites. The organism from which they take food is called the host.

E.g. Cuscuta (or Amarbel), Mistletoe, Wheat rust, corn smut etc.

Saprophytes :

The non-green plants which obtain their food from dead and decaying organic matter are called saprophytes.

E.g. Mushroom, bread mould, yeast etc.

Uses of fungi

  • Pennicillium fungus is used in making an antibiotic called penicillin.
  • Yeast is used in producing alcohol.
  • Mushrooms are used as vegetable.

Insectivorous plants :

Those green plants which obtain their food partly from insects are called insectivorous plants. These plants grow only in those soils which do not contain sufficient nitrogen mineral. These are partial heterotrophs.

E.g. Pitcher plant, Sundew, Venus fly-trap etc.

Plant nutrition
Symbiotic plants :

Some organisms live together and share shelter and nutrients. This is called symbiotic relationship.

Eg: Lichens, Rhizobium etc.

lichens is symbiosis between an algae and fungi.

  • Lichens are the indicator of air pollution.

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 converts it into a soluble form.


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