Food is a basic necessity for all living things. Plants make their own food by photosynthesis but animals cannot. Some animals directly eat plants and some eat other animals that eat plants which means that directly or indirectly, we all depend on plants for food.
MODE OF NUTRITION IN PLANTS
Plants come under the category of ‘Autotrophs’. Autotroph is made up of ‘Auto’ which means ‘self’ and ‘trophos’ which means ‘nourishment’. Animals that obtain their food from plants are called ‘Heterotrophs’. Heterotroph is made up ‘Heteros’ which means ‘other’ and ‘trophos’ which means ‘nourishment’.
Photosynthesis occurs in the leaves of the plant. The raw materials required for photosynthesis, therefore, are transported to the leaves.
The roots absorb water and minerals from the soil and transport it to the leaves through the vessels which run throughout the roots, stem, branches and the leaves.
Carbon dioxide is taken in from the atmosphere. On the surface of the leaves, there are tiny pores (called ‘stomata’) surrounded by guard cells.
The leaves also contain a green pigment called ‘chlorophyll’ which helps absorb the energy of the sunlight.
The chemical reaction of photosynthesis can be represented as:
Carbon Dioxide + Water (In Presence if Sunlight & Chlorophyll) → Carbohydrate + Oxygen
The chlorophyll containing cells use the sunlight, water and carbon dioxide to produce carbohydrates and give out oxygen. The carbohydrates get stored as starch.
Plants which do not have chlorophyll depend on other plants for their food.
There are various insect eating plants such as the Pitcher plant. Such plants are called insectivorous plants. The leaf is modified into a pitcher which has hair directed downwards. The insect gets trapped in the hair and is then digested by the digestive juice released in the pitcher.
The organisms which obtain their nutrition from dead and decaying matter are called saprotrophs. For e.g. Fungus
In a symbiotic relationship, organisms provide nutrition to each other. When crops require nitrogen to make proteins, they cannot absorb nitrogen from the air. A bacterium called Rhizobium can covert the atmospheric nitrogen into soluble form. Plants provide food and shelter to the bacteria and the bacteria in return convert nitrogen into a soluble form for the plants. These plants are generally the leguminous plants.