Definition
noun, plural: tropisms
A movement or growth response of a cell or an organism to a stimulus, which may either be positive or negative depending on the source and kind of stimulation
Supplement
A tropism is generally an involuntary orienting response of an organism to a stimulus. It is often associated with the outcome on growth rather than on the movement of an organism. This makes it different from taxis, which is a behavioral response of an organism to an external stimulus resulting in the movement of an organism either towards or away from the source of stimulation. In the same way, tropism may also be positive or negative. A positive tropism is one in which the movement or growth response of the cell or organism is towards the stimulus and negative if away from the stimulus. Tropisms are usually associated with the growth or movement responses of plants to varying exogenous stimuli. Tropism should not also be confused with kinesis, which is a movement response to a stimulus but the direction of the movement is rather random than directional as in taxis.
Tropism have many forms and they are often named according to the stimulus involved. Below are examples of tropisms:
- chemotropism
- gravitropism
- heliotropism
- hydrotropism
- phototropism
- thermotropism
- thigmotropism
- electrotropism
- ecotropism
- amphotropism
- neurotropism
- photoperiodism
Word origin: Latin tropus, English trope, Ancient Greek trópos , (tropḗ (“turn, solstice, trope”)
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