Mode of Nutrition

Plants may be able to obtain raw materials and prepare their own organic food or can be dependent on others (dead or living) for the same. They are respectively known as autotrophic (autos = self, trophien = to nourish) and heterotrophic (heteros - other, trophien - to nourish).

Autotrophic Nutrition

Autotrophs synthesize organic materials from inorganic materials. Some organisms derive their energy for this process from sunlight and are called photoautotrophs.

Example: Green plants

Other organisms use chemical energy and are called chemoautotrophs.

Example: Nitrifying bacteria. Photoautotrophs are the primary producers in food chains.

Heterotrophic Nutrition

Heterotrophs eat ready - made complex organic food. From this they obtain energy for metabolism, atoms and molecules to build new protoplasm or repair worn - out parts, and ions, co-enzymes and vitamins vital for chemical processes. There are four types of heterotrophic nutrition - saprophytic, parasitic, symbiotic and insectivorous.

Saprohytic Nutrition (sapros - rotten phyton - plant)

Saprotrophs are decomposers and liberate energy for their own use by breaking down complex organic matter from the dead bodies of other organisms. At the same time this process releases vital chemical elements into the soil which are absorbed by autotrophs. Thus saprotrophs aid the recycling of materials from dead organisms to living ones. Fungal and bacterial saprotrophs are referred to as saprophyte, while animal saprotrophs are called saprozoites.

Mucor hiemalis is a saprophyte and has their branched hyphae, providing a large absorptive surface. These penetrate dead, decaying matter and secrete enzymes into it. the food is digested extracellularly and is subsequently absorbed and transported to other parts of the fungal mycelium.

Parasitic and Insectivorous Plants

Parasites are organisms that live in or on other living organisms (called the host) generally receiving shelter and deriving nutrients from it. The parasites may cause harm to the host plant.

Stem Parasite

Cuscata is a total stem parasite. They absorb food material from host by parasitic root called haustoria.

Semi Parasite - Loranthus, Viscum

Loranthus grows on the branches of mango, fig, acacia, albizzia, etc. Its primary suckers lie outside the host and sends several haustoria into the host for withdrawing water and mineral salts.

Root Parasites

Balanophora is non-green and lives on the roots of forest roots. The aerial shoot is thick and massive monotropa (Indian pipe) aerial shoot arise from adventitious buds. The root system absorbs nourishment from the host.

Semiparasite

Partial root parasite is Santalum, sandal wood tree, an evergreen plant which grows at many places in India. Roots develop haustoria that make contact with roots of Dalbergia, Eucalyptus etc.,

Insectivorous or Carnivorous Plants

Insectivorous plants are autotrophic but obtain organic matter and animal nitrogen from insects, however not bigger than the size of a grasshopper.

There are about 450 species of insectivorous plants.

Drosera or Sundew

Herb with 6 - 12 leaves which are radical and form rosette. They have long petioles. Lamina is spoon shaped with tentacles which have swollen reddish tip. The tip is glandular and secretes a sticky purple juice which shines in the sun like dew drops. Hence the name sundew. When insects are attracted towards the leaves, tentacles bend and completely entrap the insects which get digested. Tentacles now straighten and become ready to catch another insect.

Dionea or Venus Fly Trap

The plant possess a rosette of large radical leaves. Petiole is winged and constricted at the point of union with lamina, tip is notched. The margin is slightly curved and bears 12 - 29 spiny teeth. On upper surface of lobe are present three highly sensitive spines called trigger hairs. Lamina consists of digestive glands.

Dionea or Venus Fly Trap

When an insect happens to alight on the surface of the lamina, the spines are touched and stimulated. The two lobes of lamina snap together. The marginal spines get interlocked and insects is trapped. The digestive glands secrete juice and digest the insects and absorbed. The leaf now opens and remains of insects fall down.

Nepenthes or Pitcher Plant

Leaves are large and alternate. Petiole is tendrillar. The lamina proper is modified into a large pitcher, the leaf apex serving as lid.

Nepenthes or Pitcher Plant

The pitcher attracts insects due to its gaudy colour and nectar. The insects roam into neck of pitcher in search of more nectar. The lid closes and digestive glands digest the insects.

Utricularia or Bladder Wort

It is rootless aquatic plant with segmented leaves. Some leaves are modified into small shortly stalked bladder. At the narrower end is an opening guarded by valve like structure.

Utricularia or Bladder Wort

On the outer surface are bristles and sensitive hair. The external glands secrete digestive juice. When insects alights, valve opens and insect passes in the bladder. It gets digested inside.

Chemosynthesis

Chemoautotrophs are (organisms) bacteria using CO₂ as a carbon source and energy derived from the oxidation of inorganic materials such as iron, sulphur, ammonia and nitrite. Chemosynthesis is thus a process of carbohydrate synthesis, in which organisms use chemical reactions to obtain energy from inorganic compounds. These bacteria are particularly important in nitrogen fixation, nitrification and denitrification.

Nitrogen Fixation

Nitrification