Chemotaxis is the directed movement of cells or organisms towards or away from a chemical stimulus, playing a crucial role in processes like immune response, development, and bacterial behavior. 

Thermotaxis is the directional movement of an organism in response to a temperature gradient. 

Positive thermotaxis refers to the movement of an organism towards a warmer temperature or heat source. Conversely, negative thermotaxis is the movement away from warmer areas or heat sources. Thermotaxis can be crucial for survival and reproduction in various organisms, helping them find optimal temperature conditions or respond to environmental cues. 

phototaxis refers to the directional movement of an organism, or part of an organism, in response to light, either toward (positive phototaxis) or away from (negative phototaxis) a light source.