Tropism

Tropism

A tropism (from Greek, "tropos", to turn) 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" or "cell tropism" in which case tropism refers to the way in which different viruses/pathogens have evolved to preferentially target specific host species, or specific cell types within those species. The word tropism comes from the Greek "trope" ("to turn" or "to change"). Tropisms are usually named for the stimulus involved (for example, a "phototropism" is a reaction to light) 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 in sometimes derisive way 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.

Types of tropisms

*Chemotropism, movement or growth in response to chemicals
*Gravitropism (or geotropism), movement or growth in response to gravity
*Hydrotropism, movement or growth in response to moisture or water
*Heliotropism, movement or growth in response to sunlight
*Phototropism, movement or growth in response to lights or colors of light
*Thermotropism, movement or growth in response to temperature
*Thigmotropism, movement or growth in response to touch or
*Host tropism or cell tropism, the host range of pathogens
**Ecotropism, limited host range (e.g. infects only one species or cell type)
**Amphotropism, wide host range (e.g. infects many species or cell types)
**HIV tropism, the means of entry into cells used by a given strain of HIV
** Neurotropism, a virus that preferentially infects the host's nervous system.

ee also

*Rapid plant movement


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  • tropism — TROPÍSM, tropisme, s.n. Tendinţă de acomodare şi de orientare a unui organism vegetal fixat de pământ, într o anumită direcţie, sub influenţa unei excitaţii exterioare ca lumina, căldura, gravitaţia, umiditatea etc. – Din fr. tropisme. Trimis de… …   Dicționar Român

  • -tropism — [trə piz΄əm] [< TROP(E) + ISM] combining form forming nouns tropism [heliotropism] …   English World dictionary

  • tropism — [trō′piz΄əm] n. [< TROPISM] the positive, or negative, attraction of a plant or sessile animal toward, or away from, a stimulus, as in the turning of a sunflower toward the light tropistic adj …   English World 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… …   The Collaborative International Dictionary of English

  • tropism — 1899, tendency of an animal or plant to turn or move in response to a stimulus, abstracted from geotropism, ult. from Gk. tropos (see TROPE (Cf. trope)) …   Etymology dictionary

  • tropism — ► NOUN Biology ▪ the turning of all or part of an organism in response to an external stimulus. ORIGIN from Greek tropos turning …   English terms dictionary

  • tropism — noun Etymology: International Scientific Vocabulary tropism Date: 1899 1. a. 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… …   New Collegiate Dictionary

  • tropism — n. [Gr. tropos, turn] A movement, orientation or locomotion of a motile organism in response to a stimulus. a. Positive tropism: toward the stimulus. b. Negative tropism: away from the stimulus; see taxis …   Dictionary of invertebrate zoology

  • tropism — tropismatic /troh piz mat ik/, adj. tropistic /troh pis tik/, adj. /troh piz euhm/, n. Biol. an orientation of an organism to an external stimulus, as light, esp. by growth rather than by movement. [1895 1900; independent use of TROPISM] * * * ▪… …   Universalium

  • -tropism — trəˌpizəm, in some words .ˌtrōˌpizəm noun combining form ( s) Etymology: International Scientific Vocabulary, from trope (I) + ism : tendency to turn toward : affinity for : tropism …   Useful english dictionary

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