Tropism is the response of a plant or certain animals to a stimulus that makes them orientate themselves with greater intensity from one direction to another. It is the biological ability of these organisms to move by themselves in response to various forms of external stimuli, whether light, wind, chemicals, touch, temperature, gravity and others. Although plant hormones have a lot to do with how a plant responds and moves according to its environment, the subject of tropisms in general is still a very interesting phenomenon among the scientific community.
It is the displacement carried out by plants or organisms as a response to stimuli presented in nature, that is, a series of stimuli that come to them from outside.
Tropism consists of a series of movements that produce a change in the direction of growth and that occur due to a series of stimuli or external factors. It is a very common movement system, especially in plants, although it can happen in some types of living organisms such as fungi and viruses. Changes in direction will always depend on stimuli.
Contrary to a learned skill, innate reactions are genetically programmed. In this way tropic organisms will naturally turn to a stimulus. A stimulus can be any signal from the environment, and individual tropisms are often named after the stimulus that causes the movement.
There are two types of tropism, the negative and the positive. When the movement is given in the direction of the stimulus, it is said that it is a positive tropism, otherwise, when the movement is given against the stimulus, then we are talking about a negative tropism.
Tropism is classified as follows:
There are many other tropisms in nature, due to the great variety of stimuli that organisms can perceive. For example:
Seen from a cellular and biological point of view, we also find a type of tropism called “viral tropism”. This occurs when a type of virus has a highly specific attraction to a particular cell. Viruses are able to develop a specific ability that allows them to attack the cells by selecting which one to attack.
In the area of psychology, tropism refers to the ability of individuals to acquire new functions through experience. These functions are gained thanks to the learning that the individuals have. Depending on the species, it will be tropism. Psychological tropism is also governed by reflexes, which are linked to the physical and chemical characteristics produced by stimuli.
The difference between tropism and nastia is that tropisms are changes produced by a positive or negative stimulus but that occur permanently. The nastias produce the same results, but they are temporary changes, this means that the plant at some point will return to its original state.
Non-climbing plants will respond to the constant presence of a good sized object by varying the route of its stems and trying to escape into the open air, especially if the object in question restricts their sunlight, water or growth space.
When there are earth movements that leave exposed the roots of a tree, these will look for the air and, they will try to get into the ground, whatever the cost, since they will not be able to extract their nutrients from the air.
Briceño V., Gabriela. (2019). Tropism. Recovered on 7 October, 2021, de Euston96: https://www.euston96.com/en/tropism/