Tropism
Overview
 
A tropism is a biological phenomenon
Phenomenon
A phenomenon , plural phenomena, is any observable occurrence. Phenomena are often, but not always, understood as 'appearances' or 'experiences'...

, indicating growth
Growth
Growth refers to an increase in some quantity over time.The quantity can be:*Physical *Abstract ....

 or turning movement of a biological organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

, usually a plant, in response to an environmental stimulus
Stimulus (physiology)
In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....

. 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
Host tropism
Host tropism is the name given a process of tropism that determines which cells can become infected by a given pathogen. Various factors determine the ability of a pathogen to infect a particular cell. Viruses, for example, must bind to specific cell surface receptors to enter a cell...

" 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.
Encyclopedia
A tropism is a biological phenomenon
Phenomenon
A phenomenon , plural phenomena, is any observable occurrence. Phenomena are often, but not always, understood as 'appearances' or 'experiences'...

, indicating growth
Growth
Growth refers to an increase in some quantity over time.The quantity can be:*Physical *Abstract ....

 or turning movement of a biological organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

, usually a plant, in response to an environmental stimulus
Stimulus (physiology)
In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....

. 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
Host tropism
Host tropism is the name given a process of tropism that determines which cells can become infected by a given pathogen. Various factors determine the ability of a pathogen to infect a particular cell. Viruses, for example, must bind to specific cell surface receptors to enter a cell...

" 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. Tropisms are usually named for the stimulus involved (for example, a phototropism
Phototropism
Phototropism is directional growth in which the direction of growth is determined by the direction of the light source. In other words, it is the growth and response to a light stimulus. Phototropism is most often observed in plants, but can also occur in other organisms such as fungi...

is a reaction to light) and may be either positive (towards the stimulus) or negative (away from the stimulus).

Tropisms are typically associated with plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s (although not necessarily restricted to them). Where an organism is capable of directed physical movement (motility
Motility
Motility is a biological term which refers to the ability to move spontaneously and actively, consuming energy in the process. Most animals are motile but the term applies to single-celled and simple multicellular organisms, as well as to some mechanisms of fluid flow in multicellular organs, in...

), movement or activity in response to a specific stimulus is more likely to be regarded by behaviorists as a taxis
Taxis
A taxis is an innate behavioral response by an organism to a directional stimulus or gradient of stimulus intensity. A taxis differs from a tropism in that the organism has motility and demonstrates guided movement towards or away from the stimulus source ...

(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
    Chemotropism
    Chemotropism is growth of organisms such as bacteria and plants, navigated by chemical stimulus from outside of the organism....

    , movement or growth in response to chemicals
  • Geotropism (or gravitropism), movement or growth in response to gravity
  • Heliotropism
    Heliotropism
    Heliotropism is the diurnal motion of plant parts in response to the direction of the sun.It is found in some members of family Malvacea e.g Malva or Lavetara...

    , movement or growth in response to sunlight
    Sunlight
    Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

  • Hydrotropism
    Hydrotropism
    Hydrotropism is a plant's growth response in which the direction of growth is determined by a stimulus or gradient in water concentration...

    , movement or growth in response to water
    Water
    Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

  • Phototropism
    Phototropism
    Phototropism is directional growth in which the direction of growth is determined by the direction of the light source. In other words, it is the growth and response to a light stimulus. Phototropism is most often observed in plants, but can also occur in other organisms such as fungi...

    , movement or growth in response to lights or colors of light  (e.g.- the sunflower
    Sunflower
    Sunflower is an annual plant native to the Americas. It possesses a large inflorescence . The sunflower got its name from its huge, fiery blooms, whose shape and image is often used to depict the sun. The sunflower has a rough, hairy stem, broad, coarsely toothed, rough leaves and circular heads...

    )
  • Thermotropism
    Thermotropism
    Thermotropism or thermotropic movement is the movement of a plant or plant part in response to changes in temperature. A common example is the curling of Rhododendron leaves in response to cold temperatures.-External links:*...

    , movement or growth in response to temperature
    Temperature
    Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

  • Electrotropism
    Electrotropism
    Electrotropism is a kind of Tropism which results in growth or migration of an organism, usually a cell, in response to an exogenous electric field...

    , movement or growth in response to an electric field
    Electric field
    In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...

  • Thigmotropism
    Thigmotropism
    Thigmotropism is a movement in which an organism moves or grows in response to touch or contact stimuli. The prefix thigmo- θιγμος comes from the Greek for "touch". Usually thigmotropism occurs when plants grow around a surface, such as a wall, pot, or trellis. Climbing plants, such as vines,...

    , movement or growth in response to touch or contact
  • Host tropism
    Host tropism
    Host tropism is the name given a process of tropism that determines which cells can become infected by a given pathogen. Various factors determine the ability of a pathogen to infect a particular cell. Viruses, for example, must bind to specific cell surface receptors to enter a cell...

     or cell tropism, the host range of pathogen
    Pathogen
    A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

    s
    • Ecotropism
      Ecotropism
      Ecotropism or ecotropic indicates that a pathogen like a virus or a bacterium has a narrow host range and can infect only one or a small group of species or cell culture lines.- See also :* Tropism, a list of tropisms...

      , limited host range (e.g. infects only one species or cell type)
    • Amphotropism
      Amphotropism
      Amphotropism or amphotropic indicates that a pathogen like a virus or a bacterium has a wide host range and can infect more than one species or cell culture line....

      , wide host range (e.g. infects many of entry into cells used by a given strain of HIV)
    • Neurotropism
      Neurotropic virus
      A neurotropic virus is a virus which is capable of infecting nerve cells, or which does so preferentially. Such viruses thereby largely evade the usual immune response—which acts only within the blood system.- Terminology :...

      , a virus
      Virus
      A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

       that preferentially infects the host's nervous system.
    • Photoperiodism
      Photoperiodism
      Photoperiodism is the physiological reaction of organisms to the length of day or night. It occurs in plants and animals.Photoperiodism can also be defined as the developmental responses of plants to the relative lengths of the light and dark periods...

      , is response to seasons
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK