All living organisms require food. The food gives energy to the organisms for growth and maintenance of their body functions. Carbohydrates, proteins, fats, vitamins and minerals are the components of food. These components of food are necessary for our body and are called nutrients.
Nutrition is the process of taking food by an organism and its utilisation by the body. Green plants prepare their own food while humans and animals are directly or indirectly dependent on plants for their food.
Modes of Nutrition
On the basis of a different mode of nutrition, organisms are categorised into two major types, i.e.
(i) Autotrophs (auto-self, trobpos-nourishment) Autotrophic nutrition is the mode of nutrition in which organisms make their own food from the simple substance (e.g. CO2 and H2O) by the process of photosynthesis. Therefore, plants are called autotrophs.
(ii) Heterotrophs (heteros-other) Humans and animals do not contain chlorophyll and are dependent on plants for their food in readymade form. Those organisms which cannot prepare their own food and take food from green plants or animals are called heterotrophs and the mode of nutrition is called heterotrophic nutrition.
Photosynthesis: Food Making Process in Plants
The process by which autotrophic green plants make their own food from simple inorganic substances (carbon dioxide and water) in the presence of sunlight and green pigment or chlorophyll is known as photosynthesis.
Process of Photosynthesis
The process of photosynthesis takes place in the leaves, the “food factory” of the plants.
- Carbon dioxide is taken in through tiny pores on the leaves called stomata.
- Water and minerals that are required for the process are transported to the leaves from the roots through the stem.
- Chlorophyll helps the leaves use the energy from the sunlight to prepare food using the carbon dioxide, water and minerals.
- Oxygen is released as a by-product of this process.
- The equation can be given as:
All living organisms are made from small building units of catted cells. Cells are the structural and functional units of the body of all living organisms. They can only be seen under a microscope. The cell has a thin outer boundary called cell membrane, a distinct, centrally located spherical structure called nucleus and jelly-the substance surrounding the nucleus called cytoplasm.
The inorganic raw material, i.e. CO2 is taken from the air through the tiny pores present on the surface of leaves called stomata and water is absorbed through the roots of plants (from the soil) and is transported to leaves by vessels which act like pipes. These vessels form the continuous path from roots to leaves for the movement of nutrients.
Green plants possess chlorophyll in their leaves which captures the energy of the sunlight. This light energy is used to prepare food (starch). During the process, oxygen is also released. Photosynthesis is the unique process in which solar energy is captured by the leaves and stored in the plants in the form of food. Thus, ‘Sun is the ultimate source of energy for all the living organisms.’
Importance of Photosynthesis
If the plants do not perform photosynthesis, there would be no food on earth. Photosynthesis is also necessary for the production of oxygen gas in the atmosphere which is necessary for the respiration of organisms. Therefore, it can be said that no life is possible in the absence of photosynthesis.
Other Modes of Nutrition
Organisms that live together and share their shelter and nutrients are said to be in a 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.
- This association works well for both the fungi and the tree.
- Another most common example is of Rhizobium bacteria.
- They reside in the root nodules of leguminous plants.
- The bacteria provide a plant with nitrogen that they fix and in turn, they get shelter and food from the plant.
- Rhizobium is a type of bacteria that convert atmospheric nitrogen into a soluble form that can be utilised by plants (nitrogen fixation).
- It usually resides in the roots of leguminous plants like peas, gram, moong etc and is instrumental in providing these plants with a rich source of nitrogen.
- Nitrogen is an important nutrient required for soil and for plants.
- However, nitrogen in the atmosphere is not easily accessible.
The process by which nitrogen is converted into a form that can be used by plants and other living organisms is called nitrogen fixation.
A parasite is a heterotroph that completely depends on another organism for its food.
- The organism to which the parasite latches onto is called the host.
- The host, in the process, is deprived of all nutrients for its own growth as they are consumed by the parasite.
- For example, Cuscuta (Amarbel) is a nongreen plant that takes readymade food from the plant on which it is growing.
Organisms which rely on dead and decaying matter for their food are called Saprotrophs.
- This mode of nutrition is called saprotrophic nutrition.
- For example, Fungi.
- Fungi secrete digestive juices on the dead and decaying matter and convert it into a solution.
- Then they absorb the nutrients from it.
Plants that feed on insects are called Insectivorous plants.
- These plants are green and carry out photosynthesis.
- But, they grow in nitrogen-deficient soils.
- So, in order to get nitrogen, they feed on insects.
- These insectivorous plants have their parts modified for attracting and catching insects.
- For example, The pitcher plant, Venous flytrap