THE PROPERTIES AND FUNCTIONS OF THE CELL

CONTENT

1. The Cell’s Reactions to its Environment
2. Movement
3. Reproduction

The Cell’s Reactions to its Environment

The protoplasm of plant and animal cells is irritable. It can detect and respond to the changes in their environment. Any change in conditions which is enough to produce a change in the activities of an organism or its part is called a stimulus.

Types of Responses

The three responses of the cell to its environment are tactic, nastic and tropic responses.

A. Tactic Responses (Taxism)

It is a response made by a whole organism or its freely locomotive parts in response to an external stimulus. Types of tactic responses are:

(i) Phototactic (Phototaxis): response to variation and intensity of light e.g. in free swimming Euglena, Chlamydomonas etc.

(ii) Chemotactic (Chemotaxis): response to the presence of chemical substances e.g. chemotactic movement of Amoeba away from an acidic environment.

(iii) Aerotactic (Aerotaxis): response to the source of oxygen

(iv) Osmotactic (Osmotaxis): response to variation in osmotic concentration

B.