Nastic movements are rapid, reversible responses to non-directional stimuli (eg. Temperature, Humidity, Light irradiance). Nastic movement is caused by turgor pressure change due to movement of water in cells as opposed to tropic movement which is actual growth and therefore irreversible. The rate or frequency of these responses increases as intensity of the stimuli increases. An example of such a response is the opening and closing of flowers (photonastic response). Nastic responses are usually associated with plants. They are named with the suffix "-nasty" and have prefixes that depend on the stimuli:

• Photo- response to light
• Chemo- response to chemicals or nutrients
• Hydro- response to water
• Thermo- response to temperature
• Geo-/Gravi- response to gravity
• Thigmo-/Hapto- response to touch

Also see Taxis, Kinesis and Tropism for other types of movement.

Biology