A tropism (from Greek τρόπος, tropos, "a turning") is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. In tropisms, this response is dependent on the direction of the stimulus (as opposed to nastic movements which are non-directional responses). Viruses and other pathogens also affect what is called " host tropism", " tissue tropism", or "cell tropism", or in which case tropism refers to the way in which different viruses/pathogens have evolved to preferentially target specific host species, specific tissue, or specific cell types within those species. Tropisms are usually named for the stimulus involved (for example, a phototropism is a reaction to sunlight) and may be either positive (towards the stimulus) or negative (away from the stimulus).
Tropisms are typically associated with plants (although not necessarily restricted to them). Where an organism is capable of directed physical movement ( motility), movement or activity in response to a specific stimulus is more likely to be regarded by behaviorists as a taxis (directional response) or a kinesis (non-directional response).
In English, the word tropism is used to indicate an action done without cognitive thought: However, "tropism" in this sense has a proper, although non-scientific, meaning as an innate tendency, natural inclination, or propensity to act in a certain manner.
In botany, the Cholodny–Went model, proposed in 1927, is an early model describing tropism in emerging shoots of monocotyledons, including the tendencies for the stalk to grow towards light ( phototropism) and the roots to grow downward ( gravitropism). In both cases the directional growth is considered to be due to asymmetrical distribution of auxin, a plant growth hormone.
The Collaborative International Dictionary
Tropism \Tro"pism\ (tr[=o]"p[i^]z'm), n. [Gr. troph` a turning, tre`pein to turn + -ism.] (Physiol.) Modification of the direction of growth, caused by some external influence, such as light; -- sometimes used for motion of an organism toward or away from an external stimulus, more properly called taxis.
Douglas Harper's Etymology Dictionary
n. 1 (context biology English) the turning of an organism in response to a stimulus, either towards or away from the stimulus 2 (context virology English) viral tropism, or which type of tissue supports a certain virus
n. an involuntary orienting response; positive or negative reaction to a stimulus source
Usage examples of "tropism".
Perhaps an advanced tropism of some sort, although that does tend to suggest organic intelligence, hmmm?
This may be their basic tropism, the inherent behavioral pattern of their race .
For one thing, a tropism involves the movement of only a portion of an organism such as the root or the stem whereas an animal is likely to move as a whole.
Already he had acquired the strange tropism that attracted him to metals and repelled him from daylight.
The tropism guided him, but he was terrified lest he reach a dead end.
MBL has grown slowly but steadily from the outset, sprouting new buildings from time to time, taking on new functions, expanding, drawing to itself by a sort of tropism greater numbers of biological scientists each summer, attracting students from all parts of the world.
She found herself drifting, realized she was being drawn by some journalist tropism toward Cluster 3, the function rooms clumped beyond the circular escalator well.
He saw the huge lumbering bird twitch toward him as by a tropism, then come speeding.
Had he truly been that adolescent, crouched breathless in an alley behind a dumpster, acknowledging for the first time the undeniable tropism of sexuality?
They take to such things by the same simple tropism that makes plants strain toward the sun or attracts bees to bright colors.
Perhaps their more human half had also played a role, giving them a tropism for dancing flames, for a circle of illumination to bar the surrounding dark.
Nevertheless, the responses of even very simple animals are generally more complicated than those of plants, and to call those responses tropisms would be wrong.
The tropisms of plants and the taxis of simple animals are generalized responses of an entire organism or of a major portion of one to a very generalized stimulus.
The various reflexes I have been talking about are, like the tropisms of plants and the taxis of simple animals, examples of innate behavior behavior that is inborn and does not have to be learned.
After he has arrived at that point, all his mental processes are suspended except those elementary ones, not much more than tropisms, that are concerned with the mechanics of the carnal act itself.