Plant movement: Taxes

A taxis is the movement of an entire cell or organ in response to and directed by an external stimulus. That is, a taxis is a change in direction of locomotion in a motile micro-organism or cell, made in response to certain types of external stimulus.

Taxic responses are restricted to cells that possess cilia, flagella, or some other means of locomotion. The term is usually not applied to the movements of higher animals.

Just like tropic movements, tatic movements are either postive or negative.

Types of taxes or tactic movement

Phototaxis

A movement of an entire palnt cell or organ in responsve to light. Euglena, chlorplast, fruits, etc move towards light and are said to be postively phototactic.

Chemotaxis

This type of tactic movement has as stimulus external chemical substances. Chemotaxis is the movement of an organism in response to a chemical stimulus. Somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment.

For example, sperm cells of Liverworth move towards substances released by the ovum during fertilisation (postively chemotactic).

Geotaxis

Geotaxis, also known as gravitaxis, is movement of an organism, organ or a cell in response to gravity. Moving in the direction of gravity is positive geotaxis, while movement in the opposite direction is negative geotaxis.

Magnetotaxis and Reotaxis

Magnetotaxis is a plant movement where an organ or cell move in response to magnetic fields. This type of movement is common among motile bacteria.

Reotaxis involves movement with response to resistance. Rheotaxis is a form of taxis seen in many aquatic organisms like afish whereby they will turn to face into an oncoming current.

In a flowing stream, this behaviour leads them to hold their position rather than being swept downstream by the current.