Heterotrophic Nutrition in plants I Chapter 12 I Nutrition I class 11 I First year I Lec# 03

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METHODS OF PLANT NUTRITION
The plants generally obtain their food from the air or the water in which
they grow. There are, however, some special method s of nutrition, which are
described below.
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Saprophytic Nutrition
Definition.
Feeding on dead and decaying matter such as dead leaves in the soil or
rotting tree trunks is called saprophytic nutrition and derives its nutrients
from host plants.
Mode of nutrition.
They produce extracellular enzymes, which digest the decaying matter and
then absorb the soluble products back into their cells.
Some bacteria break down the proteins of dead plants and animals and
release nitrates which are taken up by the plant roots and then built into
new amino acids and proteins, thus helping in nitrogen cycle.
Parasitic Nutrition
Definition.
Feeding by living in or on other organism (host) belonging to different species
is called parasitic nutrition. Parasites attach themselves to living things or
their host, for nourishment.
Mode of nutrition.
For obtaining nourishment from higher plant the parasite penetrates its
suckers in the conducting tissue of the host.
Examples.
Puccinia is a parasitic fungus that destroys the wheat plant. Dodder
(Cuscuta) is a leafless plant that lives as a twining parasite.
Symbiotic Nutrition
Definition.
It is a mutual nutrition between organisms living in association with one
another. These organisms belong to two different species. Some important
examples are lichens, mycorrhiza and root nodules with nitrogen fixing
bacteria.

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Lichen
It is made up of a fungus and alga cells. The alga makes food by
photosynthesis, while the fungus supplies water and minerals and also
protection against desiccation.
Mycorrhiza.
It is s an association between a fungus and roots of higher plants. The fungus
depends upon the photosynthate of the plant.
Benefits
The benefit derived by mycorrhiza plant is not properly understood.
Possibly the Mycorrhizal fungus benefits the plant by decomposing organic
material in the soil and providing water and minerals such as phosphorous to
plant.
However, it is known that the plants with mycorrhiza association show better
growth than those without fungal partner.
Root Nodules.
Leguminous plants have nodules on their roots, which contain nitrogen fixing
bacteria .The bacteria live on the plant material and fix nitrogen, converting
it into nitrates, which the plant uses.