Plant Movements:Movement refers to the act of moving or changing its position. The act of moving from one place to another is known as locomotion, whereas the plants movements are not considered locomotion because they have their roots fixed in one place. However, in plants, we can see different types of movement for their growth, development, and reproduction. Examples of plant movements include roots growing downward, stomata opening and closing, petals opening, etc.
In this article, we have provided detailed information on plant movements. Students can go through this article and find definitions of plant movements, types of movement in plants, seismonastic movement and much more. Continue reading to gain a thorough understanding of plant movements and Make no mistakes on questions about plant movements in the exam.
Plant Movements: Definition
Plants do not have a nervous system, but they respond to various stimuli like light, temperature, touch, water, etc., which can be observed by their different movements called plant movements. As a result of external or internal stimuli, plants move their parts.
Plant movements can be divided into two on the basis of the criteria, which is responsible for the movement to take place:
Fig: Flow Chart Showing Classification of Plant Movements
1. Movements of Locomotion
It refers to the movement of the whole plant body from one place to another. Like that of male gametes of Bryophytes and Pteridophytes. Male gametes here are flagellated and move from one place to another, i.e. from the male reproductive part to the female gamete. This type of movement can be autonomic (spontaneous) or paratonic (induced).
i. Autonomic movements a. Ciliary Movements – This type of movement is seen in some organisms having cilia or flagella. Like movements seen in Chlamydomonas, Volvox, etc. b. Amoeboid Movements – This type of movement is due to the formation of pseudopodia. Like in Amoeba, amoeboid movement is seen to capture food. c. Cyclosis- It refers to the protoplasmic movement of a cell. It can be rotational movement or circular movement. Example- Chara, Hydrilla exhibit rotational movement while trichomes or staminal hairs of Tradescantia (spiderwort) shows protoplasmic movement in a circular manner.
ii. Paratonic (Induced) movement or Tactic movements
It refers to the movement of locomotion which is due to external stimulus. This type of movement is directional. a.Phototactic– Here, the external stimulus is light. Light induces locomotion in certain organisms like Chlamydomonas that have flagellated structures. It swims towards the light. Other examples can be seen in the case of Euglena, which is considered as a link between plants and animals. It has a plant-like structure called the chloroplast. So if the light is there, it moves towards light and can perform photosynthesis. If the light is not there, then it will start eating other organisms like animals. b. Chemotactic– Here, the external stimulus is chemical, i.e. Chemicals are responsible for the movement of the plant. Example- Male gamete of Bryophyte fern moves from antheridium to archegonium due to chemicals secreted by archegonium. Chemical secreted here is sucrose and malic acid produced by archegonium. c.Thermotactic– Here, the external stimulus is temperature. Cells with flagella move towards the warmer temperature because the enzymatic activity is optimum in warmer conditions. Example- This can be seen in Chlamydomonas that will move towards the warmer side called positive thermotaxis while if the temperature is too high, then it will move away from the high temperature and is called negative thermotaxis.
2. Movements of Curvature
The movement of curvature is due to the bending of some plant parts. This is divided into-
a. Autonomic (Spontaneous)- In this, no external stimulus is present. This is further divided into- i. Autonomic movement of curvature due to variation- There occurs bending in plants due to turgor pressure which is due to endo or exosmosis. Like periodic up and down movements of leaflets in a Telegraph plant. This happens due to the gaining and losing of water by the leaflets. When the cells of leaflets lose water, they drop down, but when they gain water due to endosmosis, then they move up. ii. Autonomic movements of curvature due to growth- There occurs bending in plants due to unequal growth of the organs of the plants. It can be of the following types-
1. Nutation– This type of movement is seen in growing tips of vine or tendril. In this, there are differences in the growth of different parts of the plant. When tendril is given support, its side, which is attached to the support, grows at a slower rate than the part or side of the tendril which is away from the support, i.e. part of the tendril which away from the support will grow at a faster rate, which results in bending and twining of the plant around that support.
2. Nastic– There occur differences in the growth of different surfaces of organs of plants. Like if movement occurs due to the fast growth of the upper surface of the organ of a plant, then this type of movement is called epinastic movement. If movement occurs due to the fast growth of the lower surface of the organ of a plant, then this type of movement is called hyponastic movement.
b. Paratonic (Induced)– This type of movement of curvature is caused by external stimuli. It is further divided into the following two types:- i. Tropic (Growth movements) or Tropism- These movements are directional. Movements can be towards or away from the stimulus.
1. Geotropic– It refers to the tropic movement which occurs in response to gravity. Here gravity acts as an external stimulus. These types of movements are called geotropic movements, and the phenomenon is called geotropism. It can be positive or negative geotropism. Like we can take the example of the growth of roots. This movement is taking place towards the gravity so-called positive geotropism. In contrast, the growth of the stem is away from gravity, so it shows negative geotropism.
Fig: Positive and Negative Geotropism
2. Phototropic– It refers to the tropic movement which occurs in response to light. Here light acts as an external stimulus. These types of movements are called phototropic movements, and the phenomenon is called phototropism. Like bending the stem of a growing plant towards the light source.
3. Thigmotropic– It refers to the movement of plants in response to touch. This movement is directional, and the movement is called thigmotropic movement, the phenomenon is called thigmotropism. Curling movement of tendrils of Passiflora around support are examples of thigmotropic plants.
Fig: Response of ‘Tendril’ to Touch
4. Chemotropic– Movement in response to the chemicals are called chemotropic movement and the phenomenon is called chemotropism. E.g. growth of pollen tubes. 5. Hydrotropic– Growth movements in response to the water or movement of water in plants are called hydrotropic movements and the phenomenon is called hydrotropism. Growth of roots towards the source of water shows hydrotropism. 6. Thermotropic – If the tropic movement occurs due to the stimulus temperature, then that type of movement is called thermotropic movement. 7. Aerotropic– If air is the stimulus and growth is due to this stimulus, then it is called aerotropic movement, and the phenomenon is called aerotropism. ii. Nastic (Variation movements)- These movements are not unidirectional.
1. Photonasticmovement– Here, the stimulus is a change in light intensity. This movement is seen in the noon flowers, in which flowers open up in sunlight and then close when the intensity of light decreases. 2. Nyctinastic movement – It refers to the rhythmic nastic movements which occur day and night. Some of the legumes close their leaves at night and open up during daylight. This is called sleep movement in plants. 3. Thermonasticmovement – It refers to the non-directional movement of plants in response to temperature. Flowers open up as the temperature increases. E.g. The leaves of Oxalis triangularis fold up as temperature decreases. 4. Thigmonastic or seismonasticmovement – This type of movement occurs in response to touch. Like in “Touch me not” plant.
As soon as we touch the leaves of this plant, a chemical is released, which is transported through the xylem and phloem to the pulvinus (swollen base of the leaves). Once the chemical reaches the pulvinus, the inner cells actively loose K+ ions to the outer cells. As a result of which the inner cells will become hypotonic, and outer cells become hypertonic. As water moves from hypotonic to hypertonic medium, water molecules from inner cells move out. Due to which inner cells become loose, and outer cells become turgid. Due to which both the sides of the leaves will come closer to each other or bend towards the central axis. Then again, after some time, the inner cell becomes turgid, and levees will open up again. This thigmonastic in Mimosa pudica was explained by Snow and Bose.
Fig: Bending of Leaves of Mimosa pudica
Fig: The Leaves of Sensitive Plant Fold due to the Loss of Water from pulvinus at their Base
Plant movement refers to the movements of the organs of the plants in response to external or internal stimuli. It can be spontaneous or induced. Plants respond to light, gravity, temperature, chemical, air, touch, and water to move. All of these are stimuli for the plants. In some of the plants like Chlamydomonas, Volvox, Amoeba, etc., locomotion is observed in response to light or food, etc.
Frequently Asked Questions (FAQs) on Plant Movements
Here are some of the common questions which students may have in mind regarding Plant Movements:
Q.1. What is the major function of Plant Movements? Ans:Plant movement is important for the growth, development and survival of the plants.
Q.2. Explain Plant Movements with examples? Ans: Plant movements refer to the movement of the plant organs in response to internal or external stimuli. Like the growth of the stem of the plants towards light is called phototropic movement. The growth of roots towards gravity is called geotropic movement. If growth occurs towards any chemical released, then it is called a chemotropic movement, like the growth of a pollen tube.
Q.3. What are the different types of plant movement? Ans: a. Geotropic movement b. Phototropic movement c. Thigmotropic movement e. Chemotropic movement f. Hydrotropic movement g. Thermotropic movement h. Aerotropic movement
Q.4. Why is movement in plants important? Ans: Plant movement is important for growth, survival and reproduction in plants.
Q.5. What are growth movements? Ans:Growing plants move their organs in response to external stimuli in order to grow and survive. As an example, phototropism refers to the tendency of a stem to move towards the light in order to grow and survive.