An Introduction
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 Movement in Plants (Tropism)
1. What is Tropic Movement? Explain with an example.
Tropic movement in plants is the directional response to the presence of external stimuli. Such movements usually occur in the presence of external factors like – light, temperature, gravity, water, etc.
2. What Different Types of Movements can be Observed in Plants?
Typically, there are six types of tropism – i. Phototropism, ii. Geotropism, iii. Hydrotropism, iv. Chemotropism, v. Thigmotropism and vi. Thermotropism. Each of the directional movements manifests in response to different environmental stimuli.
3. Explain any Three Directional Movements in Plants.
Phototropism is a directional movement that is a reaction to light. In geotropism, movement manifests as a reaction to gravity. Similarly, thermotropism is a reaction to the change in temperature.
4. Why do plants show tropic movement?
Tropic movements can be best explained as a movement in plants that helps them to survive in a particular environmental condition. For a long period of time evolution has been a matter of discussion. As evolution is just a result of changing environmental conditions, tropism can be the best example to sustain and survive with the ever-changing climatic condition.
5. What is the difference between a tactic and tropic movement?
Tactic movements are directionless. These are fully independent and are the types of locomotion movements. These are not at all affected by stimuli from outside. The tropic movements follow all the criteria which are opposing the mentioned criteria of a tactical movement.
6. How tropic movements are affected by auxin?
Oxygen is a chemical released by plants. The function of this chemical is that it moves to the target side of the plant. Due to this reason, the cells there grow larger than their corresponding cells which are present on the lighter side. This in return forms a curving of the plant stem tip toward the light, giving rise to the process which we know as phototropism.
7. How are curved shoots of seedlings measured?
The process with which the curved shoots of seedlings are measured is a very simple way. To quantify the curvature, this is simply very necessary to measure R, the radius of curvature. Place the circle accurately under the region of examination, to fit the curve at a given point. The measured radius will be the radius of curvature. This is how the measurement of curved shoots of seedlings is done.
8. Why do seedlings grow taller in the dark?
Seedlings mostly grow taller in the dark. This phenomenon occurs due to the presence of extra energy that has been stored up throughout the day by the plant which gets used up. So, they will not require light until this is depleted. But the plants should not be left in the dark for a long time. It can harm the growth as well as the life of a plant.
