How do unicellular organisms respond to stimuli? Give examples.

The simplest forms of irritability are characteristic of microorganisms (bacteria, protozoa, unicellular algae and fungi). For example, an ordinary amoeba moves in the direction of food, and green euglena moves to the illuminated part of the reservoir, since. she needs light for photosynthesis. The response motor reactions of unicellular organisms to a directionally acting environmental stimulus are called taxis. Light (phototaxis), temperature (thermotaxis), chemicals (chemotaxis), and food (trophotaxis) can be irritants. Taxis can be positive if the body moves toward the stimulus, and negative if the body moves away from it. An example of negative chemotaxis is the response of ciliates to the salt crystals placed in a drop of water.

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