Types of Tropic Movements in Plants with Mechanism and Examples
A biological phenomenon that indicates growth or turning movements in plants due to the influence of the environment is termed tropic movement in plants or tropism in plants.
In English, the word tropism means an action done in a very unthoughtful manner. But here tropism is a very directional process. In general, tropism is described as 3 step process which includes
sensation to a stimulus, as a living being, it becomes a beneficiary factor for the plants.
Signal transduction occurs( in simple words, the environment reaction towards the plant)
And finally, the directional growth response takes place.
These are the following steps that give rise to tropism or what we call "tropic movements in plants".
Tropism is seen not only in plants but also in viruses, pathogens and other biological organisms also. This phenomenon is direction-dependent and reacts according to the direction of the stimulus. Other types of tropism in different organisms are also called host tropism, tissue tropism or cell tropism.
Types of Movements in Plants
In plants, there are five types of tropic movements. These tropic movements can be explained as described below:
Phototropism
sunlight is a major source that helps plants to sustain life. This type of tropism in plants occurs due to the response to lights. In general, the plants will grow in the direction of light. It can be positive if the reaction is towards the light and it can be negative if the reaction is away from light.
Geotropism
When plants show movement in the direction of gravity the roots will grow downwards and hence shows positive geotropism. Similarly, if its shoots will grow upwards, then the process can be defined as negative geotropism.
Chemotropism
Apart from the environmental factors, there are some chemical factors also which involve the tropic movements. The movement in seed plants while transferring pollen grains to the female gamete releases some chemicals; this process leads to positive chemotropism.
Hydrotropism
When the movement of plants occurs due to the stimulus of water then the phenomenon is termed hydrotropism. This process leads to roots growing towards the area where water is present.
Thigmotropism
The movement of reflex of a plant takes place in response to touch gives rise to thigmotropism. A very common example of this kind of tropism occurs in the touch me not plant. As soon as one touches the leaves of this particular plant they droop.
In the case of phototropism or geotropism (also known as gravitropism), directional growth occurs due to the asymmetric distribution of the chemical substance known as "Auxin".
Tropism in plants is a process of growth of the plant shoots and roots in accordance with the natural environment surrounding it.
FAQs on Tropic Movements in Plants and Their Biological Basis
1. What are tropic movements in plants?
Tropic movements in plants are directional growth responses of plant parts toward or away from an external stimulus. These movements occur due to unequal growth on different sides of a plant organ in response to stimuli such as light, gravity, water, or touch.
- They are permanent growth movements.
- The direction of growth depends on the direction of the stimulus.
- They are commonly seen in roots and shoots.
2. What are the main types of tropic movements?
The main types of tropic movements are classified based on the type of stimulus causing the response. The major types 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 in plants?
Phototropism is the growth movement of a plant part in response to light. In most plants, shoots show positive phototropism by bending toward light.
- Light causes redistribution of the hormone auxin.
- Auxin accumulates on the shaded side of the shoot.
- This causes faster cell elongation on that side, bending the shoot toward light.
4. How does geotropism work in roots and shoots?
Geotropism is the growth response of plants to gravity, with roots and shoots responding differently.
- Roots show positive geotropism by growing downward toward gravity.
- Shoots show negative geotropism by growing upward away from gravity.
- This response is regulated by the redistribution of auxin in response to gravitational pull.
5. What is the difference between positive and negative tropism?
The difference between positive and negative tropism lies in the direction of growth relative to the stimulus.
- Positive tropism means growth toward the stimulus (e.g., roots toward gravity).
- Negative tropism means growth away from the stimulus (e.g., shoots away from gravity).
6. What is thigmotropism with an example?
Thigmotropism is the directional growth response of a plant to touch or physical contact. It is commonly observed in climbing plants.
- Tendrils of plants like pea or cucumber coil around a support when they touch it.
- Cells on one side grow faster, causing the tendril to curl.
7. What role does auxin play in tropic movements?
Auxin is a plant growth hormone that regulates tropic movements by causing unequal cell elongation.
- It redistributes to one side of the plant organ in response to a stimulus.
- In shoots, higher auxin concentration promotes cell elongation.
- In roots, high auxin concentration can inhibit elongation.
8. What is hydrotropism in plants?
Hydrotropism is the growth response of plant roots toward water. It ensures that roots grow in the direction of moisture in the soil.
- Roots show positive hydrotropism.
- This response helps plants absorb sufficient water.
- It is especially important in dry soil conditions.
9. How is chemotropism important in flowering plants?
Chemotropism is important because it guides the pollen tube toward the ovule during fertilization.
- Chemical substances secreted by the ovule attract the pollen tube.
- The pollen tube grows toward higher chemical concentration.
- This ensures successful fertilization in flowering plants.
10. What is the difference between tropic movement and nastic movement?
The main difference is that tropic movements are directional growth responses, while nastic movements are non-directional responses.
- Tropic movement depends on the direction of the stimulus and involves growth (e.g., phototropism).
- Nastic movement does not depend on stimulus direction and is often due to turgor changes (e.g., folding of Mimosa leaves).
