Plants obtain their nutrition by various modes. The mode of nutrition can be autotrophic mode or heterotrophic mode. Plants can be classified into autotrophs and heterotrophs.
- Autotrophic plants can synthesize their own food by the process of photosynthesis.
- Heterotrophic plants can be further classified into parasites, saprophytes and symbiotic plants.
Autotrophic mode of nutrition - Photosynthesis
It is an autotrophic mode of nutrition. Plants absorb carbon dioxide from air and water from the soil which are used as raw materials. The green pigment chlorophyll present in the leaves absorbs energy from sunlight to carry out the synthesis of food. Plants by the process of photosynthesis can produce glucose as food. Oxygen is released as by-product in this process.
Facts about photosynthesis
- Leaves are considered as food factories of a plant.
- Roots absorb water and minerals from the soil.
- Stomata present in the lower epidermis of the leaf take in carbon dioxide from the air.
- Chlorophyll present in the leaf captures energy from sunlight.
- Plants synthesize glucose using carbon dioxide and water in the presence of sunlight.
- Oxygen and water are released as by-products through the stomata during daytime.
- The food synthesized is transported to other parts of the plant.
All chlorophyll-containing plants, including algae, and some plants with red, brown or other dominant pigments, make their food by photosynthesis.
Glucose is a carbohydrate. Glucose synthesized by the process of photosynthesis is then converted into complex compounds like starch and cellulose. Starch is stored in different parts of the plant.
Plants also prepare proteins with the help of nitrogen which is obtained from the soil.
Thus, the minerals dissolved in water are used to convert sugar into carbohydrates, proteins and fats.
The food components stored form the source of energy for other heterotrophic plants and animals.
Heterotrophic mode of nutrition
This type of nutrition can be categorized into parasitic mode, saprophytic mode and symbiotic mode of nutrition. Heterotrophic plants do not possess chlorophyll. Therefore, they cannot produce their food using the process of photosynthesis.
Heterotrophic plants obtain food from other plants by following either a parasitic, saprophytic or symbiotic mode.
In parasitic mode of nutrition, plants depend on other plants or animals for their nourishment. Such plants are called as parasites and the ones on which parasites depend are called as hosts.
The insectivorous mode of nutrition is observed in plants like pitcher plant and the Venus fly trap. They purely depend on other insects and small animals for their nutrition.
Cuscuta is a parasitic plant which develops special roots called haustoria. Haustoria penetrate deep into host plant tissues and just absorb the nutrients from them.
The plants which exhibit saprotrophic mode of nutrition are called as saprotrophs. Saprotrophs are the plants that obtain their nutrition from dead and decaying organic matter. Saprotrophs secrete digestive juices onto dead and decaying matter to dissolve it and then absorb nutrients from it.
In symbiotic mode, plants develop a special relationship with certain organisms to obtain nourishment. Such plants are called as symbionts.
Plants cannot utilize atmospheric nitrogen directly. Hence, leguminous plants establish a symbiotic relationship with bacteria like Rhizobium.
Both the organisms of symbiotic relationship are mutually benefited. Leguminous plant provides shelter and nourishment for the bacteria and in turn bacteria fix atmospheric nitrogen to the plant.