A life is a sense of balance among the several activities. These activities include growth, nutrition, reproduction, excretion, etc. Both animals and plants are two different forms of living organisms. Therefore the pathway, which they follow for numerous life processes are also different.
For example, animals can run away from their predators but plants cannot do. Plants have their own mechanism to counteract the danger they face.
Nervous system and endocrine system are the two different systems in the animal body which is involved in balancing and controlling different types of the activities. In the case of plants, they are completely devoid of the nervous system and other special organs. However, plants learn to respond to different stimuli by certain movements. This response may be rapid movements like semi monastic movement or slow process like tropism. Sensitive plants show semi monastic movement in response to touch. Thus we can classify the plant movements into two types: Tropic movements and nastic movements.
Let us see different types of tropic movements in plants and how plants control and coordinate in brief.
When a plant shows some growth movement in response to a stimulus, it is known as tropism. Tropism is a direction, which is specific and depends on the direction of the stimulus. Plants may either show a positive or negative movement as a response to a stimulus. If the movement is towards the direction of stimuli, it is known as positive tropism, if the movement is away from the stimuli, it is known as negative tropism. Discussed below are a few types of tropism.
Phototropism: Plants grow towards or away from the light, the type of tropism in the response to light is called phototropism. In general, the stems usually show positive phototropism, while roots show negative phototropism. Leaves also positively respond toward the source of light.
Gravitropism: It is a type of tropism where plants show some growth in response to the gravity. Stems are negative to the gravitropism while roots are positive to the gravitropic. This is also referred to as geotropism. Among different parts of plants, the primary roots and certain other portions of the root system show positively geotropic by growing directly towards the center of gravity. The stems are called as the negatively geotropic as they grow away from the center of gravity. The leaves are transversely geotropic as they select their positions at right angles to the center of gravity.
Chemotropism: There are few chemical substances, which are actively responsible for bringing a curvature movement in plant organs. When plants grow in response to certain chemicals, this type of response is known as chemotropism. Few examples of chemotropism movements are the conversion of a flower into fruit, the growth of a pollen tube down the style during fertilization movement of tentacles in Drosera, etc.
Thigmotropism: The growing or developing movements made through plants in response to contact with a solid object are called thigmotropism. These type of movements are usually seen in tendrils and twiners. This movement is also referred to as Haptotropism.
Hydrotropism: The movement or the growth of a plant in relation to the stimulus of water are called hydrotropic movements and the equivalent response to the stimulus of water is called hydrotropism. In this type of movement, roots show the positive hydrotropic response, as they move and grow towards the water.
Thermotropism: It is the form of a tropic movement in which a plant or a part of the plant respond to the changing atmospheric temperature. For example, this type of movement is usually seen in the plants of Rhododendron. Here leaves starts twisting or bending in response to cold temperatures.
These are the six different types of tropisms which help plants to be more adaptive and help in their survival. The positive response of stems towards light helps plants in photosynthesis and the positive response of roots towards the gravity helps in the absorption of minerals and water from the soil.
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