Tropism Definition Types Mechanism and Plant Examples
Tropism is the natural ability of an organism to transform or change in response to a stimulus. Natural responses are genetically programmed rather than acquired abilities. Tropism causes an organism to spontaneously move towards a stimulus. Individual tropisms can be any signal from the setting, which are also called after the stimulus that triggers the movement. In an optimistic tropism, the animal would transform towards stimulation. In a negative tropism, the animal would move away from the tropism. Since certain stimuli are either beneficial or harmful to an organism, they are genetically ingrained. Tropism triggers the taxis which are said to be in movements.
Tropism in Viruses
Viruses and other pathogens may also cause what is known as "host tropism," "tissue tropism," or "cell tropism," which refers to how various viruses/pathogens have evolved to preferentially target particular host organisms, tissues, or cell types inside those species. Tropisms are named for the stimulus they are reacting to (for example, a phototropism is a reaction to sunlight) and may be positive (towards the stimulus) or negative (against the stimulus) (away from the stimulus).
Different Types of Tropism
Phototropism
Gravitropism
Chemotropism
Thigmotropism
Hydrotropism
Thermotropism
Magnetotropism
Phototropism
In response to light plants generally grow towards or away from the light, this type of tropism is called phototropism. In plants, the stems and leaves show positive phototropism, and roots show negative phototropism.
Gravitropism
In response to gravity, certain plants show some growth in response to gravity, this type of tropism is called Gravitropism. Stems respond negatively to gravitropism and roots respond positively to gravitropism. This is also called geotropism. Among different parts of plants, the roots show positive geotropism when directed towards the center of gravity. The stems show negative geotropic as they grow against the center of gravity.
Chemotropism
The chemical substances in a plant that are responsible to bring a curvature movement in plant organs. When plants start to grow in response to certain chemicals, then it is called chemotropism. A few instances of chemotropic movements are the transformation of the flower into fruit, the tentacles movement in Drosera, etc.
Thigmotropism
The growth or development of movements made through plants in response to a solid object contact is called thigmotropism. These types of movements are common in tendrils and twiners. This movement is known as Haptotropism.
Hydrotropism
In relation to the stimulus of water, the movement or the growth of a plant is called hydrotropic movement is called hydrotropism. In this type of movement, roots respond positively, as they move and grow towards the water.
Thermotropism
In response to the changing atmospheric temperature, tropic movement of plants or a part of the plant is called Thermotropism. For example, the Rhododendron plant.
Magnetotropism
Many animals may be attracted to certain poles by magnetic fields that serve as a source of direction.
Types of Tropism in Virus
Wide Host Range: amphotropic (e.g. infects many species or cell types)
Small Host Selection: ecotropism (e.g. infects only one species or cell type)
HIV tropism refers to how a particular strain of HIV enters cells.
A virus that preferentially infects the nervous system of the host is known as neurotropism.
FAQs on Tropism in Plants and Its Biological Significance
1. What is tropism in plants?
Tropism is the directional growth response of a plant toward or away from an external stimulus. It allows plants to grow in response to environmental factors such as light, gravity, water, and touch. In tropism:
- The response is directional and depends on the direction of the stimulus.
- It involves differential growth on one side of the plant organ.
- It is commonly observed in stems, roots, and tendrils.
2. What are the different types of tropism?
The main types of tropism are classified based on the type of stimulus causing the growth response. These include:
- Phototropism – response to light
- Geotropism (Gravitropism) – response to gravity
- Hydrotropism – response to water
- Thigmotropism – response to touch
- Chemotropism – response to chemicals
3. What is phototropism?
Phototropism is the growth of a plant part in response to light. Shoots usually show positive phototropism by bending toward light, while roots often show negative phototropism by growing away from light. This response occurs due to uneven distribution of the plant hormone auxin, which causes cells on the shaded side to elongate more, leading to bending toward the light source.
4. How does auxin control tropism in plants?
Auxin controls tropism by causing unequal cell elongation on different sides of a plant organ. The process works as follows:
- Auxin redistributes in response to a stimulus like light or gravity.
- It accumulates more on one side of the stem or root.
- Cells on that side elongate more (in stems), causing bending.
5. What is the difference between positive and negative tropism?
Positive tropism is growth toward a stimulus, while negative tropism is growth away from a stimulus. For example:
- Plant shoots show positive phototropism by growing toward light.
- Roots show positive geotropism by growing toward gravity.
- Shoots show negative geotropism by growing away from gravity.
6. What is geotropism (gravitropism)?
Geotropism, also called gravitropism, is the growth response of a plant to gravity. In this process:
- Roots grow downward showing positive geotropism.
- Shoots grow upward showing negative geotropism.
- Specialized cells called statocytes help detect gravity.
7. What is hydrotropism in plants?
Hydrotropism is the growth response of plant roots toward moisture or water. Roots show positive hydrotropism by growing toward areas with higher water concentration. This response:
- Helps plants absorb sufficient water.
- Is especially important in dry soil conditions.
- Works alongside geotropism to guide root growth.
8. What is thigmotropism with example?
Thigmotropism is the directional growth response of a plant to touch or physical contact. A common example is:
- Tendrils of pea plants or grapevines coiling around a support.
9. What is chemotropism in plants?
Chemotropism is the growth response of a plant part to chemical stimuli. A key example is:
- The growth of the pollen tube toward the ovule during fertilization.
10. How is tropism different from nastic movement?
Tropism is a directional growth response to a stimulus, while nastic movement is a non-directional movement that does not depend on the direction of the stimulus. Key differences include:
- Tropism involves growth and is usually slow and permanent.
- Nastic movements are often rapid and reversible.
- Example of tropism: stem bending toward light.
- Example of nastic movement: closing of Mimosa pudica leaves when touched.
