The phenomenon, observed in living organisms, of moving toward (positive t.) or away from (negative t.) a focus of light, heat, or other stimulus; usually applied to the movement of a portion of the organism as opposed to taxis, the movement of an entire organism. [G. trope, a turning]
- viral t. the specificity of a virus for a particular host tissue, determined in part by the interaction of viral surface structures with host cell-surface receptors.
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tro·pism 'trō-.piz-əm n involuntary orientation by an organism or one of its parts that involves turning or curving by movement or by differential growth and is a positive or negative response to a source of stimulation also a reflex reaction involving a tropism
tro·pis·tic trō-'pis-tik adj
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tro·pism (troґpiz-əm) [Gr. tropē a turn, turning] the turning, bending, movement, or growth of an organism or part of an organism in response to an external stimulus. Such response may be either positive (toward) or negative (away from) the stimulus. Cf. taxis (def. 1).Medical dictionary. 2011.