Living organisms react differently to the stimulus present in the environment.
Living organisms react differently to the stimulus present in the environment. In this article, you will find out how plants, especially their roots and shoot, react to directional stimuli. Though plants lack a nervous system, sense organs and muscles, they respond to environmental stimuli – touch, light, water, gravity, etc. That being said, let’s find out more about tropic movement in plants and its different types in detail. What are Tropic Movements in Plants? One can define tropic movement or tropism as the directional movement of particular parts of a plant in response to environmental stimuli. Notably, the movements are slow and are either towards the stimulus or away from it. Generally, a stimulus can either be positive or negative. To elaborate, a stimulus would be positive if a plant moves towards it. On the other hand, if the plant moves away from it, the stimulus would be considered negative. Types of Movements in Plants There are six types of tropic movement in plants; they are the following –
This directional movement occurs in response to light. Notably, not all parts of the plant show uniformity in their reaction towards the light. For instance, the stem and shoot move towards the source of light, showing positive phototropism. Alternatively, roots tend to move away from the light source, indicating negative phototropism. Check the image below to understand positive phototropism better. [Image will be Uploaded Soon]
This tropism occurs in reaction to chemical stimuli. It is a common occurrence in flowering plants. These following are some examples of chemotropism in flowering plants –
In geotropism, plants’ movement is in response to gravity. In such a setup, roots grow downwards indicating a positive geotropism. Conversely, the stem grows in the upward direction signifying a negative geotropism. Notably, in prostrate plants stems lose their negative geotropism and may develop into tubers or rootstock. Also, you may have often noticed the right-angled position of leaves against the centre of gravity. It signifies that leaves of a plant are transversely geotropic. [Image will be Uploaded Soon]
It is essentially a movement in reaction to the presence of water. The resulting motion is known as a hydrotropic movement. Take a look at the figure below. You will notice that plant roots incline towards the direction of the water. Thus, indicating a positive reaction. [Image will be Uploaded Soon]
Typically, the growth or movement is in response to a contact established with a solid surface or object. Thigmotropism is quite common in climbers like money plants, green peas, etc. The phenomenon is quite noticeable in their tendrils and twiner. DIY: Draw a diagram of climbers showing thigmotropism and label it.
A response towards a change in atmospheric temperature is known as thermotropism. Two examples of this tropic movement in plants are – the curling of leaves in Rhododendron and Mimosa pudica leaves. Test Your Knowledge: Which of these does not act as a stimulus for plants?
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Ans. 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.
Ans. 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.
Ans. 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.