Taxes in animals, Biology tutorial


A taxis (plural taxes) is an innate behavioral response through an organism to a directional stimulus or gradient of the stimulus intensity. Taxis distinct from a tropism (that is, turning response, frequently growth towards or away from a stimulus) in that the organism consists of motility and illustrates guided movements towards or away from the stimulus source. This is at times differentiated from a kinesis, a non-directional change in activity in response to the stimulus.

Illustrations of Taxes in animals:

For illustration, flagellate protozoans of the genus Euglena move in the direction of a light source. Here the directional stimulus is light and the orientation movement is in the direction of light. This reaction or behavior is a positive one to light and particularly named 'positive phototaxis', as phototaxis is a response to a light stimulus and the organism is moving towards the stimulus. When the organism moves away from the stimulus, then the taxis is negative. Most of the kinds of taxis have been recognized and named by using prefixes to specify the stimulus which elicits the response. These comprise aerotaxis (that is, stimulation by oxygen) anemotaxis (or wind), barotaxis (or pressure), chemotaxis (or chemicals), galvanotaxis (or electrical current), geotaxis (or gravity), hydrotaxis (or moisture), magnetotaxis (or magnetic field), phototaxis (or light), rheotaxis (or fluid flow), thermotaxis (or temperature changes) and thigmotaxis (or physical contact).

Based on the kind of sensory organs present, taxes can be categorized as klinotaxes, where an organism constantly samples the environment to find out the direction of a stimulus, tropotaxes, where bilateral sense organs are employed to find out the stimulus direction, and telotaxes that are identical to tropotaxes however where a single organ suffices to establish the orientation movement.


Aerotaxis is the response of an organism to disparity in oxygen concentration and is mostly found in the aerobic bacteria.


Chemotaxis is a migratory response drawing out by chemicals: that is, a response to a chemical concentration gradient. For illustration, chemotaxis in response to a sugar gradient has been viewed in motile bacteria like E. Coli. Chemotaxis as well takes place in the antherozoids of ferns, liverworts and mosses in response to chemicals secreted through the archegonia, as well in higher animals example: Dogs for sexual attraction. 

Unicellular (example: protozoa) or multicellular (example: worms) organisms are targets of the chemotactic substances. A concentration gradient of chemicals build up in a fluid stage guides the vectorial movement of responder cells or organisms. Inducers of locomotion towards rising steps of concentrations are considered as the chemoattractants, whereas chemorepellents outcome moving off the chemical.

Chemotaxis is explained in eukaryotic and prokaryotic cells, however signaling methods (that is, receptors, intracellular signaling) and effectors are a lot different.

Energy taxis:

Energy taxis is the orientation of bacteria in the direction of conditions of optimal metabolic activity through sensing the internal energetic conditions of cell. Thus in contrast to chemotaxis (taxis in the direction or away from a particular extracellular compound), energy taxis responds on an intracellular stimulus (example: proton motive force, activity of NDPH- 1) and needs metabolic activity.


Phototaxis is the movement of an organism in response to light: which is the response to variation in light intensity and direction.

1) Negative phototaxis, or movement away from the light source, is illustrated in several insects, like cockroaches.

2) Positive phototaxis, or movement in the direction of a light source, is beneficial for phototrophic organisms as they can orient themselves most proficiently to get light for photosynthesis. Most of the phytoflagellates, example: Euglena and the chloroplasts of higher plants positively phototactic, moving in the direction of a light source. The two kinds of positive phototaxis are viewed in prokaryotes.

a) Scotophototaxis is visible as the movement of a bacterium out of the area illuminated through a microscope. Entering darkness signals the cell to reverse the direction and reenter the light.

b) A second kind of positive phototaxis is true phototaxis that is a directed movement up a gradient to the rising amount of light.


Thermotaxis is a migration all along a gradient of temperature. A few slime molds and small nematodes can migrate all along amazingly small temperature gradients of less than 0.1C/cm. They in fact make use of this behavior to move to the optimal level in soil.


Geotaxis is a response to the attraction because of the gravity. The planktonic larvae of the king crab Lithodes aequispinus utilize a combination of positive phototaxis (that is, movement in the direction of the light) and negative geotaxis (upward movement). Both negative and positive geotaxes are found in the variety of protozoans.


Rheotaxis is the response to a current in a fluid. Positive rheotaxis is exhibited by fish turning to face against the current. In a flowing stream, this behavior leads them to hold their position in a stream instead of being swept downstream. A few fish will show negative rheotaxis where they will evade currents.


Logically, magnetotaxis is the capability to sense a magnetic field and coordinate movement in response. Though, the word is generally applied to bacteria which comprise magnets and are physically rotated through the force of the Earth's magnetic field. In this situation, the 'behavior' has nothing to do with the sensation and the bacteria are much accurately explained as 'magnetic bacteria'.


Galvanotaxis or electro-taxis are directional movement of the motile cells in response to an electric field. It has been recommended that by detecting and orientating themselves toward the electric fields, cells are capable to direct their movement in the direction of the damages or wounds to repair the defect. It as well is suggested that such a movement might contribute to directional growth of cells and tissues throughout development and regeneration. This concept is based on (i) The existence of measurable electric fields which naturally take place throughout wound healing, growth and regeneration; and (ii) cells in cultures respond to applied electric fields through directional cell migration - electro-taxis or galvanotaxis.


The Phonotaxis is a movement of an organism in response to the sound.

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