Plant prepares their food themselves with the help of water, carbon dioxide and minerals. Nutrients are necessary for growth, help in repairing damaged parts and provide energy to the body.
Nutrition is the mode of taking food by an organism and its utilization by the body. There are two type of mode of nutrition, autotrophic and heterotrophic. Autotrophic organisms prepare their food themselves from simple substances like plants, while animals and other organism, which depend on readymade food prepared by the plants are called heterotrophs.
Photosynthesis is the process by which plants make food. In this process, the conversion of light energy into chemical energy take place.
In photosynthesis, carbon dioxide and water combine in the presence of light to form sugar.
Carbon dioxide from air is taken in through the tiny pores present on the surface of the leaves. These pores are known as stomata. Xylem in the vein carries water to the food-making cells. The water comes from the roots and the root hairs, which are in the ground.
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.
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.
Some plants depend on the food produced by other plants because they do not have chlorophyll.
Cuscuta (Amarbel) is a small parasitic plant which contains no chlorophyll. They climb on other plants, which act as a host, and they take readymade food from that plant.
There are few plants, which are insectivorous and can trap insects and digest them. E.g., Pitcher plant.
When an insect lands in the pitcher, it gets trapped insect inside the plant. The insect is digested by the digestive juices secreted in the pitcher.
A saprotroph is an organism that obtains its nutrients from dead and decaying matter. E.g., fungi.
The fungi secrete digestive juices on the dead and decaying matter and convert it into a solution. Then they absorb the nutrients from it.
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.
Lichen is an association of an alga and a fungus.
Nutrients can be replenished by adding fertilizers or by other ways. Fertilizers and other manures which are rich in nutrients are added by farmers to enrich the soil and to fulfill the nutrient requirement of plants.
After harvesting soil becomes deficient in nitrogen. This gas is present in air but plants require it in soluble form. Nitrogen fixation is the process by which nitrogen is taken from its natural, relatively inert molecular form (N2) in the atmosphere and converted into nitrogen compounds (such as ammonia, nitrate and nitrogen dioxide).
The bacterium called Rhizobium can take atmospheric nitrogen and convert it into a soluble form.