Form 1:
Nutrition in Plants and Animals

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Modes of Heterotrophism

There are four main heterotrophic modes on nutrition:

Holozoic- Where organisms ingest, digest and assimilate solid complex food substances.

Saprophytism – Where organisms feed on dead decaying matter causing decomposition.

Parasitism- a feeding association in which one organism (parasite) feeds on or obtain nutrients on another organism, the host.

Symbiosis/Mutualism- An association where two organisms live together and mutually benefit from each other.

a) Parasitism

There are two main types of parasites:

Endo parasites- Live inside the host.

Ecto-parasites- Found on the external surface of the host.

The parasite benefits but the host does not. Some of the parasites cause diseases to the hosts and damage their tissues thereby weakening them.


Image:tsetse fly

b) Symbiosis

In saprophytism, both organisms benefit:

Symbiotic relationships include:

• Rhizobium and leguminous plants: rhizobium fixes nitrogen for the legume while the bacteria obtains manufactured food from the legumes.

• Lichen: association of fungi (absorbing water and nutrients) and algae (manufacturing food for the association)

• Catalase digesting bacteria and ruminants.

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