Mode of Nutrition in Plants
Autotrophic Nutrition: is the type of nutrition in which organic compounds are manufactured from available inorganic raw material taking from surroundings. Sometimes organic molecules are manufactured from single inorganic molecules by using energy produced by the oxidation of certain inorganic substances such as ammonia, nitrates, nitrites, ferrous ions, H2S and etc. This type of nutrition is called chemotrophic nutrition and process of manufacturing food is called chemosynthesis. Green plants obtain energy from sunlight and therefore are called photoautotrophs. The process of synthesizing food in plant is called photosynthesis.
Heterotrophic Nutrition: Certain non-green plants, such as fungi, bacteria and certain angiospermic flowering plants fail to synthesize their own organic food. These plants are dependent on some other external source of their nutrition. Such plants which are dependent on some other sources of their nutritional requirement are called heterotrophic plants. The heterotrophic plants are categorized into 4 main groups as follow:
Saprophytic Plants: Those plants which grow and live on dead and decaying organic matter of animals and plants are called saprophytic plants, e.g. many fungi and bacteria, Neottia (Bird’s nest orchid), grow on humus rich soil and Monotropa (Indian pine), grows on humus rich soil of pine forests.
Parasitic Plants: The parasitic plants grow and obtain their organic food from other living organisms. The living organism from which the parasite obtains its organic food, water and minerals is called host. Haustorium (any part of the body of parasite is modified into a special organ known as haustorium) enters into the cells of host and absorbs food, water and minerals from the host, e.g. Cuscuta is a rootless, yellow coloured, slender stem with small scale leaves, which twins around the host. The parasite develops small adventitious sucking roots (haustoria) which enter the host plant and absorbs readymade food from the host.
Symbiotic Plants: refers to a partnership of two dissimilar organisms in which both are mutually benefitted. Each partner in a symbiotic association is called a symbiont, e.g. mycorrhiza (fungus-root) means a symbiotic association of fungus with the roots of higher plants in the soil.
Insectivorous Plants: Most of the green plants derive their nitrogen from the soil as solutes conducted through the root system. However, some of them get nitrogen from captured animal prey. Such plants which obtain their nitrogen from animals (insects) are called insectivorous or carnivorous plants, which usually grow in waterlogged and swampy soils deficient in nitrogenous compounds, e.g. Pitcher plant (Nepenthes), Sundew (Drosera), Venus flytrap (Dionaea) and Bladderwort (Utricularia). Nepenthes (pitcher plant), usually climbers or epiphytes and leaves are modified into pitchers. The leaf apex is modified into a small lid which covers the opening of pitcher. The mouth of pitcher is called rim which is ribbed and bears nectar secreting glands. The insects attracted towards the coloured lid and nectaries, stride along the rim of pitcher and usually result in downfall. A group of digestive and absorptive gland is situated below the waxy zone inside the upper half of the pitcher. The juices secreted by these glands help in the digestion of the drawn insects. The insect proteins are broken down to amino acids by the enzymes present in the digestive juices which are then absorbed by the plant.