Question

Write short notes on the following:
(i) Commensalism
(ii) Mutualism

Answer 1

(i) Commensalism:

It is an association or relationship between two different organisms in which one is always benefitted, while the other is neither benefitted nor harmed. A commensal may live permanently attached to its host or may live within its body. All commensalistic unions are facultative. For example, suckerfish attaches itself to the under the surface of a shark with the help of its dorsal fin, which is modified into holdfast. Suckerfish gets a free ride and remnants of food which shark eats. The shark neither benefits nor suffers in any respect.

Other examples are:

1. An orchid growing as an epiphyte on mango branch.

2. Barnacles growing on the back of a whale.

3. The sea anemone and clown fish.

(ii) Mutualism:

It is a relationship between two or more individuals of different species in which all are benefitted by one another. Mutualism may be facultative when the individuals involved in the association are capable of existing independently. It is obligatory when the relationship is imperative to the existence of one or both species.

1. Mutualism between two animal species:

A mutualistic association occurs between tickbird and the rhinoceros. The bird feeds on the skin parasites of the rhinoceros and in return the rhinoceros is relieved of irritation and obtains warning of danger when the sharp-eyed bird flies away temporarily to some nearest tree.

2. Mutualism between two plant species:

This is shown by lichen. It is an association formed jointly by algae and a fungus. The main body of a lichen is formed of fungus. The fungus provides fixation, water, minerals and shelter to the algae. The algae manufacture food not only for itself but also for the fungus.

3. Mycorrhiza: It is a mutualistic association of a fungus and the roots of the higher plants. It is mainly used in the retrieval of critical elements from organic compounds, absorption of water and protection from the soil-borne pathogenic fungi.