Types of Responses

5.1

Types of Responses

	Tropism
Definition	A response of plant in which the direction of response is determined by the external stimulus
Reason of action	Is controlled by phtohormones
Time of action	Slow and not apparent
Direction	Positive tropism: growth towards direction of stimulus Negative tropism: growth away from stimulus
Examples	Geotropism: plant response to gravity Phototropism: plant response to light chemotropism: plant response to chemical Hydrotropism: plant respose to water Thigmotropism:plant response to touch

	Nastic
Definition	A response of plant toward a stimulus but the direction of response is determined by itself,not the stimulus direction
Reason of action	Is controlled by changes of turgal pressure and some nastic responses are intended for survival
Time of action	Rapid and apparent
Examples	Photonasty: plant response to light Seismonasty: plant response to mechanical stimulus Thermonasty: plant response to changes in temperature Thigmonasty: plant response to vibration Nyctinasty: a circadian rhythm that responds towards the onset of darkness