The plants are grouped into two major categories based on their ability to prepare or obtain food.
Autotrophic plants include green plants which can prepare their own food and can live independently. From inorganic raw materials, like carbon dioxide and water they can photosynthesize with the help of chlorophyll pigments in the presence of sunlight.
Heterotrophic plants are those plants which cannot produce their own food but obtain their nutrition from other sources. These plants are of the following types: (1) parasites, (2) saprophytes, (3) symbionts, (4) epiphytes, and (5) insectivorous plants.
1. Adaptation in Plant Parasites
Dodder, a parasitic plant, has no leaves. The stem is weak, cylindrical and yellow. It coils around the host and forms suckers. From these suckers, thread-like cells grow into the host stem and are connected with the vascular bundles of the host. They get water and nutritive materials through these connections. As the plant is completely dependent on its host, it is called a total parasite.
2. Adaptation in Saprophytes
Saprophytes are those plants which do not have chlorophyll. They derive their nutrition from dead, decaying matter like bacteria and fungi. With the help of some enzymes, these plants convert organic food materials into simpler forms and absorb them.
3. Adaptation in Symbionts.
Algal partner (phycobiont) prepares food by autotrophic mode while the fungal partner (mycobiont) absorbs water and minerals which are made available to the green algae. These lichens grow in green patches over tree trunks. If one partner is separated, the other would die.
4. Adaptation in Epiphytes
Epiphytes grow on other plants. They are not dependent upon other plants for nutrition. They have two types of roots. Through clinging root it clings to the plant and absorbs nutrients from the humus (decomposed organic matter) that accumulates in the crevices of the tree. Other roots called aerial roots absorb moisture from the atmosphere.
5. Adaptation in insectivorous Plant
The pitcher plant (Nepenthese) bladderwort and Venus flytrap have insectivorous mode of nutrition. In pitcher plant the end of petiole is modified into a pitcher with a lid formed by the lamina of leaf. Because of the presence of downward pointing hooks, insects are trapped in the pitcher. The enzymes secreted at the base of pitcher slowly and gradually digest the insects.
In the aquatic plant, bladderwort, leaves are changed into bladder-like structures. These have a trapdoor and sensitive hairs. If some insects touch the sensitive hairs the trapdoor opens and water carrying the insect’s rushes inside where digestion takes place.
In venus flytrap, the leaf works as a trap in the centre the leaf works as a trap. In the centre of each half of the leaf, three sensitive hairs are found. The edges of leaves are covered with long spines. Nectar secreted by the plant attracts files to the leaf. The leaf closes immediately when the sensory hairs are touched by the flies.