One of the main properties of a living organism is its movement or response to an irritating factor. In developed organisms, the movement is called a muscle act, the implementation of which is achieved due to the influence of a nerve impulse on the muscle. However, in elementary organisms, movement and response to irritation take on a slightly different form. In general, these phenomena are combined in the concept of "taxis". This is a motor reaction of an organism, its part or an individual organelle in the direction of an irritant or away from it. In plants, the term "tropism" has a similar interpretation. Taxis and tropisms can be positive and negative.
Sources of irritation
Sources of irritation that can provoke taxis are factors of animate and inanimate nature. Any physical phenomena, biological factors, or chemicals can cause the body to move if its vital activity depends on them. For example, chemotaxis is a directed movement to the location of a chemical. If a cell moves to that molecule that has value as a metabolic substrate, then such chemotaxis is positive. Negative chemotaxis is a deliberate increase in the distance between a chemical and a cell. An example of positive chemotaxis is the movement of a white blood cell to the site of inflammation.
Negative chemical taxis are an active flight of cells or an attempt to delimit them, if substances can lead to their death. Also, the source of irritation is electromagnetic radiation with various wavelengths, liquid, soil and other factors. In each case, taxis can be positive, that is, the body, its part or its individual organoid, approaches the stimulus, or negative. Negative taxis are a deliberate increase in the distance between the body and the irritating factor.
Tropism and Taxis
Tropism is a particular example of taxis in plants. They have many landmarks with respect to which they move during life or daily cycles. For example, the tops of almost all photosynthetic plants have negative geotropism and positive heliotropism. This means that they strive to reach the sun in order to increase the efficiency of photosynthesis. Plants also have positive hydrotropism, negative thermotropism.
Specific tropisms and taxis
Having understood what taxis is in biology, the definition of specific stimuli for some organisms allows us to understand the features of their metabolism. In particular, organisms whose metabolism must proceed at high temperatures possess positive thermotropism. There is also magnetotaxis, anemotaxis (movement in the direction of the air), barotaxis, cytotaxis, rheotaxis (depending on the current in water bodies), galvanotaxis (with respect to electric current). In this case, taxis is a fundamental type of behavior of unicellular or multicellular organisms. Only in relation to the reference point, which is any of the above factors, can organisms move in living nature.