Movements in Plants
Organisms respond to external in addition to internal stimuli. Animals move in response to external stimuli; likewise, plants also show movements.
Animals alter their place in response to the stimulus. Plants are fixed for that reason; they change their growth pattern.
Plant movements include movements toward the light, opening, and closing of flowers, growth of developing roots looking for water and nutrients, etc.
Inflorescence, fruits, and shoots are all efficient in moving by picking up modifications in the environment, therefore changing their position, function, and behaviors accordingly.
Types of Movements
There are 2 types of movements:
- Autonomic movements
- Paratonic movements
1.Autonomic movements
These movements are spontaneous motions due to internal causes. Autonomic movements are of 3 types:
- (i) Tactic movements
- (ii) Turgor movements
- (iii) Growth movements.
(i) Tactic Movements
These are the movements of an entire cell or organism i.e., mobility due to internal stimulus. The tactic movement might be positive if it is towards the stimulus or negative if it is far from the stimulus.
Tactic movements are the movements of locomotion; they are additionally classified on the basis of the nature of the stimulus.
(a) Phototactic movement: It is a movement in response to the stimulus of light. The movement might be towards the source of light (positive) or away from the source of light (negative). The very best example of positive tactic movement is the passive movement of chloroplast due to cyclosis. This movement assists the chloroplast to absorb optimal light for CO2fixation. The light intensity and directions both affect the intracellular circulation of chloroplasts.
(b) Chemotactic movement: The movement in reaction to the stimulus of chemicals is called chemotactic movements. The movement shown by sperms of liver-worts, mosses, ferns towards archegonia in response to the stimulus of nucleic acid released by the ovum is one such example.
(ii) Turgor Movements
Turgor motion is because of differential modifications in turgor and size of cells as a result of gain or loss of water. Rapid movements of leaflets in “touch-me-not” plant and sleep motions of the plants fall under this category of movements,
- Sleep movements:
Bean plants and some members of the bean family lower their leaves in the evening and raise them in the morning. These are referred to as sleep movements. These sleeping movements are because of everyday changes in turgor pressure in the pulvinus. The place of attachment of leaf with the shoot, pulvinus, is a swollen part of the petiole made up of parenchymatous cells with relatively big intercellular spaces and a central strand of vascular tissues. When turgor pressure on the lower side of the pulvinus increases the leaves rise and end up being horizontal.
When turgor pressure reduces on the lower side of the pulvinus, the leaves lower and go to the “sleeping” position.
(b) Rapid movements of leaflets:
When the compound leaf of sensitive plant Mimosa is touched, the leaflets fold together. This action takes a second or two arising from rapid loss of turgor by the cells in pulvinus at the base of each leaflet. The observation has revealed that potassium (K+) ions move first, which triggers water to leave the cell by exosmosis. It takes about ten minutes to gain back the turgor and bring back the internal turgidity of the leaf.
(iii) Growth Movements
Growth movements are due to unequal growth on two sides of plant organs like stem, root, tendrils, buds, and so on. There are three kinds of growth movements.
(a) Epinasty:
It is shown by leaves, petals, etc. The upper surface area of the leaf in the bud condition shows more growth as compared to the lower surface area. This leads to the opening of buds.
(b) Hyponasty:
If development in the lower surface area of the leaf in bud condition is more than that of the upper surface area then the bud will stay closed.
(c) Nutation:
The growing tip of the young stem moves in a zig-zag style due to alternate changes in development on opposite sides of the apex. This mode of development is called nutation.
2.Paratonic Movements
These movements are due to external causes. These are of the following types.
(a) Tropic Movements
The word tropic is originated from the Greek word ‘Tropos’ meaning ‘turn’. It is the movements in the curvature of the whole organ towards or far from stimuli such as light, gravity, and touch. Following prevail tropic movements:
(i) Phototropism: It is the movement of part of the plant, in response to the stimulus of light and is triggered by the differential growth of part of a plant-like stem or root.
(ii) Thigmotropism: It is the movement in response to the stimulus of touch, for instance, climbing vines. When they are available in contact with some solid object, the growth on the opposite side of contact boosts, and the tendril coils around the support.
(iii) Chemotropism: The movement in response to some chemicals is called chemotropism. The hyphae of fungi are chemotropic.
(iv) Hydrotropism: The movement of plant parts in response to the stimulus of water is called hydrotropism. The growth of roots towards water is because of positive hydrotropism and growth of shoot away from water is negative hydrotropism.
(v) Geotropism: It is the response to gravity. Roots display positive geotropism and shoots show negative geotropism.
(b) Nastic Movements
These are the non-directional movements of parts of the plant in response to external stimuli. These are of two types:
- Nyctinasty:
The nyctinasty movements are shown by the organs in response to external stimuli resulting in differential growth. These are because of turgor and growth changes. It might be of two types:
(a) Photonasty: The principal stimulus is the photoperiod. The lowers open and close due to light intensity.
(b) Thermonasty: It is because of temperature. The lowers tulip close during the night because of rapid development in the lower side by upward and inward bending of the petals.
(ii) Haptonastic movements: take place in action to contact. Examples include the action of the Venus flytrap.
Role of Plant Growth Substances in Plant Movements
Plants do not move from one place to another like animals. However, their organs show movements, which are controlled by hormonal agents. Auxins play a significant role in phototropism. It is thought that unequal distribution of auxin indole acetic acid (IAA) in the coleoptile’s stumps, produces unequal cell augmentation, triggering a bend in the organ towards the source of light. Auxins are also responsible for positive gravitropism of roots and negative geotropism of stems.
Auxins prevent the development of root cells. The cells of the upper surface area, for that reason, elongate, and the root curves downward. Auxins, on the other hand, promote the growth of the stem cells. The cells of the lower surface area, extend and the stem curves up. Nastic movements are because of some balance or ratio between growth inhibitors (abscisins) and growth stimulators (gibberellins). Nevertheless, it has actually been observed that epinasty is because of auxins and hyponasty due to gibberellins.
MCQs on Movements in Plants
- What is the primary characteristic of Autonomic Movements in plants?
- a) Stimulus-driven
- b) External causes
- c) Spontaneous motions
- d) Growth-related
Answer: c) Spontaneous motions
- Which type of Autonomic Movement involves the movement of an entire cell or organism?
- a) Turgor Movements
- b) Growth Movements
- c) Tactic Movements
- d) Phototactic Movement
Answer: c) Tactic Movements
- What is the primary stimulus for Phototactic Movement?
- a) Temperature
- b) Light
- c) Gravity
- d) Chemicals
Answer: b) Light
- Which Autonomic Movement is characterized by the rapid movements of leaflets upon touch?
- a) Sleep movements
- b) Tactic Movements
- c) Rapid movements of leaflets
- d) Epinasty
Answer: c) Rapid movements of leaflets
- What causes the “sleeping” position in plants with sleep movements?
- a) Changes in turgor pressure
- b) Exposure to light
- c) Water absorption
- d) Growth inhibitors
Answer: a) Changes in turgor pressure
- Which Paratonic Movement is in response to touch stimuli, such as climbing vines?
- a) Thigmotropism
- b) Phototropism
- c) Hydrotropism
- d) Chemotropism
Answer: a) Thigmotropism
- What is the primary characteristic of Nastic Movements?
- a) Directional movements
- b) Non-directional movements
- c) Stimulus-driven
- d) Spontaneous motions
Answer: b) Non-directional movements
- What type of Nastic Movement is exhibited by flowers in response to light intensity?
- a) Nyctinasty
- b) Photonasty
- c) Thermonasty
- d) Haptonastic movements
Answer: b) Photonasty
- Which plant growth substance plays a significant role in phototropism?
- a) Gibberellins
- b) Abscisic Acid
- c) Auxins
- d) Cytokinins
Answer: c) Auxins
- What is the role of Auxins in gravitropism?
- a) Inhibit root cell development
- b) Promote stem cell growth
- c) Promote root cell growth
- d) Inhibit stem cell development
Answer: c) Promote root cell growth
- Which type of Autonomic Movement is due to differential changes in turgor and cell size caused by water gain or loss?
- a) Rapid movements of leaflets
- b) Growth Movements
- c) Tactic Movements
- d) Turgor Movements
Answer: d) Turgor Movements
- What is the primary stimulus for Thigmotropism?
- a) Light
- b) Touch
- c) Gravity
- d) Chemicals
Answer: b) Touch
- What is the primary stimulus for Chemotactic Movement?
- a) Light
- b) Touch
- c) Chemicals
- d) Gravity
Answer: c) Chemicals
- What type of Paratonic Movement is due to the curvature of the entire organ toward or away from stimuli like light, gravity, and touch?
- a) Tropic Movements
- b) Nastic Movements
- c) Thigmotropism
- d) Chemotropism
Answer: a) Tropic Movements
- What is the primary stimulus for Geotropism?
- a) Light
- b) Gravity
- c) Touch
- d) Chemicals
Answer: b) Gravity
- Which type of Nastic Movement is due to temperature changes?
- a) Photonasty
- b) Nyctinasty
- c) Thermonasty
- d) Haptonastic movements
Answer: c) Thermonasty
- Which Autonomic Movement is associated with the upward and inward bending of petals due to rapid development?
- a) Nyctinasty
- b) Photonasty
- c) Epinasty
- d) Haptonastic movements
Answer: c) Epinasty
- What causes the zig-zag movement of the growing tip of a young stem in nutation?
- a) Gravity
- b) Touch
- c) Differential growth
- d) Light
Answer: c) Differential growth
- What is the primary role of gibberellins in Nastic Movements?
- a) Inhibit growth
- b) Promote growth
- c) Induce sleep movements
- d) Cause rapid leaflet movements
Answer: b) Promote growth
- Which Autonomic Movement involves movements of an entire cell or organism due to internal causes?
- a) Tactic Movements
- b) Turgor Movements
- c) Growth Movements
- d) Epinasty
Answer: a) Tactic Movements
- What is the primary role of Abscisic Acid in Nastic Movements?
- a) Promote growth
- b) Inhibit growth
- c) Induce sleep movements
- d) Cause rapid leaflet movements
Answer: b) Inhibit growth
Frequently Asked Questions (FAQs):
Q1: Why do plants exhibit movements?
- A: Plants exhibit movements in response to both external and internal stimuli. While they are fixed in place, they can change their growth pattern, position, and behaviors to adapt to changes in their environment.
Q2: How many types of movements do plants have?
- A: Plants have two main types of movements: Autonomic movements and Paratonic movements.
Q3: What are Autonomic movements, and how many types are there?
- A: Autonomic movements are spontaneous motions due to internal causes. There are three types of Autonomic movements: Tactic movements, Turgor movements, and Growth movements.
Q4: What is the significance of Tactic movements?
- A: Tactic movements involve the mobility of an entire cell or organism in response to internal stimuli. They can be positive (towards the stimulus) or negative (away from the stimulus).
Q5: How do plants respond to light stimuli?
- A: Phototactic movements are plant movements in response to the stimulus of light. They can be positive (towards the light source) or negative (away from the light source).
Q6: What is the role of Auxins in plant movements?
- A: Auxins play a significant role in plant movements, including phototropism (movement towards light) and gravitropism (response to gravity). They influence cell growth and contribute to bending of organs towards light sources.
Q7: What are Turgor movements, and can you provide examples?
- A: Turgor movements result from differential changes in turgor and cell size due to water gain or loss. Examples include sleep movements in plants like the touch-me-not, where leaves raise and lower in response to daily changes in turgor pressure.
Q8: Explain the concept of Nastic Movements.
- A: Nastic movements are non-directional movements of plant parts in response to external stimuli. Examples include nyctinasty, where flowers open and close in response to light intensity, and haptonastic movements, such as those observed in the Venus flytrap in response to contact.
Q9: How do plants respond to touch stimuli?
- A: Thigmotropism is the movement in response to touch stimuli. Climbing vines, for instance, exhibit thigmotropism by coiling around a support when in contact with a solid object.
Q10: What is the role of gibberellins in plant movements?
- A: Gibberellins are involved in Nastic Movements, influencing the balance between growth inhibitors and stimulators. For example, gibberellins are associated with hyponasty in plants.
Q11: How do hormones control plant movements?
- A: Plant movements are controlled by hormones, with auxins playing a key role in phototropism and gibberellins influencing Nastic Movements. Hormones regulate cell growth and response to external stimuli.
Q12: Do all plants exhibit the same types of movements?
- A: No, different plants may exhibit various types of movements based on their species and environmental conditions. The types of movements can vary, including phototropism, thigmotropism, and other responses.
Q13: Can you explain the role of Abscisic Acid in plant movements?
- A: Abscisic Acid (ABA) inhibits growth and is involved in the regulation of Nastic Movements. It plays a role in maintaining a balance between growth inhibitors and stimulators in plants.
Q14: Why do plant organs show movements?
- A: Plant organs show movements to adapt to changes in the environment, optimize exposure to light, respond to touch or other stimuli, and enhance functions like reproduction and nutrient absorption.
Q15: How do plants respond to water stimuli?
- A: Hydrotropism is the movement of plant parts in response to the stimulus of water. Roots, for example, exhibit positive hydrotropism by growing towards water sources.
Q16: Are all plant movements visible to the naked eye?
- A: No, not all plant movements are easily visible. Some movements, like changes in turgor pressure or hormonal responses, may occur at a cellular or molecular level and may not be apparent without specialized tools.
Q17: Can plant movements be influenced by external factors?
- A: Yes, Paratonic movements, such as tropic and nastic movements, are influenced by external stimuli like light, gravity, touch, and chemicals. These movements are responses to external factors.
Q18: Are plant movements essential for their survival?
- A: Plant movements contribute to the adaptation and survival of plants by enabling them to respond to changing environmental conditions, optimize resource uptake, and enhance reproductive processes.
Q19: Do all parts of a plant exhibit the same type of movement?
- A: No, different parts of a plant may exhibit different types of movements depending on their functions and responses to stimuli. For instance, leaves, flowers, and roots may show distinct types of movements.
Summary: Movements in Plants – Autonomic & Paratonic Movements
The tutorial on “Movements in Plants – Autonomic & Paratonic Movements” provides a comprehensive exploration of how plants respond to external and internal stimuli. Divided into sections, the tutorial covers the two main types of movements observed in plants: Autonomic movements and Paratonic movements.
Key Points:
- Introduction:
- Plants, unlike animals, exhibit fixed positions but demonstrate various movements, including responses to light, gravity, touch, and more.
- Movements in plants are vital for adapting to environmental changes, optimizing growth patterns, and fulfilling essential functions such as reproduction and nutrient absorption.
- Types of Movements:
- Autonomic Movements:
- Spontaneous motions resulting from internal causes.
- Subtypes include Tactic movements, Turgor movements, and Growth movements.
- Paratonic Movements:
- Movements in response to external causes.
- Includes Tropic Movements and Nastic Movements.
- Autonomic Movements:
- Autonomic Movements:
- Tactic Movements:
- Mobility of entire cells or organisms in response to internal stimuli.
- Examples include Phototactic movement (response to light) and Chemotactic movement (response to chemicals).
- Turgor Movements:
- Result from changes in turgor pressure due to water gain or loss.
- Sleep movements and rapid leaflet movements are discussed.
- Tactic Movements:
- Growth Movements:
- Unequal growth on different sides of plant organs, leading to movements.
- Examples include Epinasty, Hyponasty, and Nutation.
- Paratonic Movements:
- Tropic Movements:
- Movements in response to stimuli like light, gravity, and touch.
- Includes Phototropism, Thigmotropism, Chemotropism, Hydrotropism, and Geotropism.
- Nastic Movements:
- Non-directional movements in response to external stimuli.
- Nyctinasty and Haptonastic movements are discussed.
- Tropic Movements:
- Role of Plant Growth Substances:
- Hormones, such as Auxins, play a crucial role in plant movements.
- Auxins contribute to phototropism, gravitropism, and overall growth regulation.
- The balance between growth inhibitors (abscisins) and stimulators (gibberellins) influences Nastic Movements.
- Conclusion:
- Plants, while rooted, exhibit a remarkable array of movements crucial for survival and adaptation.
- Understanding these movements and the role of plant growth substances can have practical applications in agriculture, horticulture, and environmental science.
This tutorial serves as a valuable resource for those seeking insights into the diverse movements displayed by plants and the underlying mechanisms governing these responses.