The tropism , is the response of a plant or certain animals to a stimulus that does directed more intensely in a direction to another. It is the biological capacity that these organisms possess to move by themselves in response to various forms of external stimuli , be it light, wind, chemicals, touch, temperatures, gravity and others. Although plant hormones have a lot to do with the way a plant responds and moves according to its environment, the topic of tropisms in general is still a very interesting phenomenon among the scientific community.


What is tropism?

It is the displacement that plants or organisms make as a response to stimuli that occur in nature, that is, a series of stimuli that reach them from outside .

  • What is tropism?
  • Types
  • Classification
  • Viral tropism
  • Tropism in psychology
  • Difference between tropism and nastia
  • Examples

What is tropism?

The 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 occur in some types of living organisms such as fungi and viruses . The changes that occur in the direction will always depend on the stimuli.


Contrary to a learned skill, innate reactions are genetically programmed. In this way organisms with tropism will naturally turn to a stimulus. A stimulus can be any signal from the environment, and individual tropisms are often named after the stimulus causing the movement.


There are two types of tropism, negative and positive . When the movement occurs in the direction of the stimulus, it is said to be a positive tropism , otherwise, when the movement occurs against the stimulus, we will then be talking about a negative tropism .


Tropism is classified as follows:

  • Phototropism : Many photosynthetic animals make their food from sunlight. Therefore, the light acts as a stimulus for many organisms causing many of them to move towards the light. For example, many algae, plankton, and small invertebrates have positive phototaxis that takes them to the same area in the ocean, which contains by far the most light. Other organisms may show a negative reaction to light and try to get away from it, such as a beetle when you uncover it from its hiding place. The beetle will seek darkness, as darkness generally means safety.
  • Heliotropism : This is similar to phototropism , but the position of the organism cannot change. This can be seen in many crops , such as sunflowers, corn, and even garden flowers. Following the path of the sun guarantees to receive the maximum amount of light
  • Gravitropism : it is known by the name of geotropism and it is a growth that occurs in response to the acceleration of gravity . The roots then sink into the soil and stem growth increases. It is very important for the correct germination of the seeds.
  • Thigmotropism – happens when, for example, a plant grows on a solid surface . This causes the plants to have developed organs to adhere to and can change the rate at which they grow to control germination.
  • Chemiotropism : it occurs in response to the responses to chemical elements that plants need to obtain different nutrients or to flee from chemical elements that cause them harm.

There are many other tropisms in nature, due to the great variety of stimuli that organisms can perceive. For instance:

  • Thermotropism : a tropism that causes organisms to move towards a specific temperature.
  • Magneto tropism : many animals can use magnetic fields as a source of direction, and be attracted to certain poles

Viral tropism

Viewed from the 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 towards a certain cell in particular. This situation occurs mainly due to the cell surface markers that the virus has. Viruses are capable of developing a specific ability that allows them to attack cells by selecting which one they are going to attack.

Tropism in psychology

In the area of psychology, when talking about tropism, it refers to the ability of individuals to acquire new functions through experiences . These functions are achieved thanks to the learning that individuals have. Depending on the species, this will be the tropism. The psychological tropism is also governed by the reflexes , which are linked to the physical and chemical characteristics that produce the stimuli.

Difference between tropism and nastia

The difference between tropism and nastia is that tropisms are changes produced by a positive or negative stimulus but that are permanent . The nastias produce the same results, but they are temporary changes , this means that the plant will at some point return to its original state.


The no creepers respond to the constant presence of an object sized varying the route of their stems and trying to escape to the outdoors , especially if the object in question restricts them sunlight, water or space growth .

When there are movements of earth that expose the roots of a tree, they will seek the air and will try to penetrate the earth , at any cost, since they will not be able to extract their nutrients from the air.

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