How do unicellulars orient themselves in the environment?

Unicellular organisms can perceive various stimuli (reference points) from the external environment and respond to them. As a rule, the response to irritation consists in the spatial movement (movement) of individuals. This type of irritation in unicellular is called taxis. Light, temperature, moisture, chemicals, food, etc. can be a source of irritation.
An active reaction to light is called phototaxis, to chemical compounds – chemotaxis, to temperature – thermotaxis, to earth attraction – geotaxis, etc. Taxis can be positive and negative. So, when green euglena tends to swim to a lighted place in a reservoir – this is a positive phototaxis, and when it floats away from a grain of salt thrown into the water – this is negative chemotaxis.

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