WBBSE Class 10 Life Science Solutions Chapter 1A Sensitivity and Response in Plants

Detailed explanations in West Bengal Board Class 10 Life Science Book Solutions Chapter 1A Sensitivity and Response in Plants offer valuable context and analysis.

WBBSE Class 10 Life Science Chapter 1A Question Answer – Sensitivity and Response in Plants

Short Answer Type Questions : 2 Marks

Question 1.
Why is a system of control and co-ordination essential in living organisms?
Answer:
Following are the reasons.

1. Increase the chances of survival by responding to stimuli.
2. Different body parts function as a single unit.
3. To maintain homeostasis.

Question 2.
How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?
Answer:
The movement of leaves of the sensitive plant (e.g. Mimosa pudica or touch me-not) occurs in response to touch or contact stimuli. It is a growth independent movement (nastic movement). The movement of shoot towards light is called phototropism. This type of movement is directional and is growth dependent.

Question 3.
Write differences between nastic and tropic movements.
Answer:

Characters	Nastic movement	Tropic movement
1. Growth	Growth Independent movements	Growth dependent movements
2. Time of Action	Immediate	Slow
3. Response to Stimules	non-directional	directional
4. Response for action	change in turgor	cell division
5. Alternate name	nastics	tropism
6. Examples	folding of leaves of touchme-not (Mimosa), opening and closing of stomata	phototropism, geotropism, hydrotropism, chemotropism

Question 4
What is chemotropism?
Answer:
Directional movement of a plant/or its part in response of chemicals is called chemotropism. e.g. growth of the pollen tube towards the ovule is a chemotropic movement due to which fertilization of flower takes place.

Question 5.
Give examples of geotropism.
Answer:
(i) Roots move in the direction of gravity (positive (+ve) geotropism)
(ii) Shoots move (up) against direction of gravity (negative (-ve) geotropism)

Question 6.
How does phototropism occur in plants?
Answer:
The growth movement in plants in response to light stimulus is known as phototropism. The shoots show positive phototropism and the roots show negative phototropism. This means that the shoots bend towards the source of light whereas the roots bend away from the light source.
For Example : The flower head of sunflower is positively phototropic and hence is moves from east to west along with the sun.

Question 7.
Write the responses of stem and root due to light and gravity.
Answer:

Part of plant	Response to light	Response to gravity
Stem	Positive phototropism (grows towards the light)	Negative geotropism (grows against the force of gravity)
Root	Negative phototropism (grows away from the light)	Positive geotropism (grows in the direction of the force of gravity)

Question 8.
Differentiate between Autonomic and Paratonic movements.
Answer:
The movements induced by some internal causes are called autonomic movement. The movement induced by external stimuli is called Paratonic movement.

Question 9.
What is phototropism? How is it caused?
Answer:
The tropic movement of the part of plant in response to stimulus of light is called phototropism. It is caused due to differential growth of part of plant like root, stem.

Question 10.
What is meant by diaphototropic?
Answer:
Leaves also show response to light. They twist their petioles and plane their faces (upper sides) at right angles to the light. They are diaphototropic or transversely phototropic.

Question 11.
What is Cholodny and Went theory of phototropism?
Answer:
Cholodny and Went theory suggested that the phototropic response occurs due to unequal distribution of auxin (IAA).

Question 12.
What is Cholodny and Went theory of geotropism?
Answer:
This theory suggests that differential growth in geotropism is caused due to unequal distribution of auxin (IAA) in the upper and lower halves of the shoot.

Question 13.
What are Seismonastic movements?
Answer:
The shock movements are called Seismonastic. It occurs in mimosa. When the leaves of mimosa, (touch me not) is touched, the leaflet folds together. This response takes within a few seconds.

Question 14.
What are Haptonastic movements?
Answer:
The nastic movements occur due to stimulus of touch are called Haptonastic movements. Haptonastic movements occur in the leaves of Drosera and Dionaea.

Question 15.
Are the development and growth of plants only influenced by plant hormones?
Answer:
Physical and chemical environmental factors, like intensity and position of light in relation to the plant, gravitational force, temperature, mechanical pressures and chemical composition of the soil and the atmosphere, can also influence the growth and development of plants.

Question 16.
What are plant tropisms?
Answer:
Tropisms are movements caused by external stimulus. In Botany the studied plant tropisms are : phototropism (tropism in response to light), geotropism (tropism in response to the earth gravity) and thigmotropism (tropism in response to mechanical stimulus).

Question 17.
To which direction does the growth of one side of a stem, branch or root induce the structure to curve?
Answer:
Whenever one side of a stem, branch or root grows more than the other side, the structure curves towards the side that grows less.

Question 18.
What is phototropism?
Answer:
Phototropism is the movement of plant structures in response to light. Phototropism may be positive or negative. Positive phototropism is that in which the plant movement (or growth) is towards the light source and negative phototropism is that in which the movement (or growth) is inverse, away from the light source.

Phototropism relates to auxins since the exposition of one side of the plant to light makes these hormones concentrate in the darker side. This fact makes the auxin action upon the stem to be positive, i.e., the growth of the darker side is more intense and the plant arcs towards the lighter side. In the root (when submitted to light, in general experimentally) the auxin action is negative (over the positive range), the growth of the darker side is inhibited and the root curves towards this side.

Question 19.
What are the types of plant geotropisms? Why do the stem and the root present opposite geotropisms?
Answer:
The type of geotropisms are the positive geotropism, that in which the plant grows in favour of the gravitational force, as for example in roots, and the negative geotropism, that against the gravitational force, for example, in the stem. Root geotropism and stem geotropism are opposed due to different sensitivities to auxin concentration in a horizontal position (parallel to the ground) and naturally auxins concentrate along their bottom part.

Under this condition it is observed that the stem grows upwards and the root grows downwards. This happens because in the stem the high auxin concentration in the bottom makes this side grow (longitudinally) more and the structures arc upwards. In the root the high auxin concentration in the bottom inhibits the growth of this side and the upper side grows more making the root to curve downwards.

Question 20.
What is thigmotropism?
Answer:
Thigmotropism is the movement or growth of the plant in response to mechanical stimuli (touch or physical contact), as when a plant grows around a supporting rod. It occurs for example in grape and passionfruit vines, coiling of tendrils and steams, haustoria in Cuscuta etc.

Question 21.
What will happen if apical bud is removed?
Answer:
Removal of apical bud shows lateral branching. This is because auxins control apical dominance and apex inhibits the growth of axillary buds.

Question 22.
What do mean by paratonic movement?
Answer:
Plants have the capacity of changing their position, in response to external or internal stimuli which are known as plant movements. The movements which occur due to internal stimuli are called autonomic movements and those that occur due to external stimuli are called paratonic movements.
Nepenthes (pitcher plant) is an insectivorous plant. In this, the leaf lamina is modified to form a pitcher and leaf apex froms a coloured lid.

Question 23.
If a tree flowers thrice in a year (Oct., Jan and July) in Northern India, then it is said to be photo and thermo-intensitive. Why?
Answer:
Flower formation is a transitional phase in the life cycle of plant. During flowering, vegetative shoot apex is converted into reproductive shoot apex. The physiological mechanism for flowering is controlled by 2 factors ; photoperiod or light period, i.e., photoperiodism and low temperature, i.e., vernalization.

Question 24.
Explain thigmonastic movement with the example of the ability of the Venus Flytrap to capture insects.
Answer:
Thigmonastic movements are exhibited by some insectivorous plants such as Dionaea, venus Flytrap, Drosera etc. These plants have tentacles, which are sensitive to the stimulus of touch. In the case of the venus flytrap turgor pressure changes, occur in which hydrogen ions are rapidly pumped into the walls to cells on the outside of each leaf in response to the action potentials from the trigger hairs. The protons apparently loosen the cell walls so rapidly that the tissue actually becomes flaccid so that cells quickly absorb water, causing the outside of each leaf to expand and the trap to snap shut.

Question 25.
What do you mean by movement of locomotion and movement of curvature?
Answer:
Movement may be of two types, movement of locomotion and movement of curvature. Movement of curvature is movement of individual parts in relation to other parts. Curvature movement may be growth movements and turgor movements. Growth movements are caused by differential growth in different parts of an organ. Opening of floral buds into flowers is such a type of growth movement. Mostly floral bud opening shows thermonastic movement i.e. opening and closing are controlled by temperature. Sometimes movements are controlled by presence or absence of light, e.g. Oxalis.

Question 26.
What is the cause of leaflet movement in Desmodium?
Answer:
The leaflet of the Desmodium plant automatically goes up and down with the loss and gain of turgidity of the lateral leaflets. As the leaflets go down, they lose turgidity, become light and go up.

Question 27.
What is Clinostat?
Answer:
The geotropic movement demonstrated in the laboratory by an instrument is called Clinostat.

Question 28.
What is seismonasty?
Answer:
The movement which is induced by stimuli like touch, shock, shaking etc is called seismonastic movement or Seismonasty.

Question 29.
What is nastic movement?
Answer:
The movement of a plant organ that has no relation to the direction of stimulus but has a relation with the intensity of stimulus is called nastic movement.

Question 30.
What is geotropic movement?
Answer:
The movement of curvature of plant organ that is induced by force of gravity is called geotropic movement.

Question 31.
What is hydrotropic movement? Give example.
Answer:
The movement of curvature of plant organ in response of water stimulus is called hydrotropic movement. E.g. Root is positively hydrotrophic and stem is negatively hydrotropic.

Question 32.
Write two difference between tropic and nastic movement.
Answer:

Tropic movement	Nastic movement
i. This movement is related to growth.	i. This movement is related to turgor.
ii. The movement bears relation to the direction of stimulus.	ii. The movement bears relation to the intensity of stimulus.

Question 33.
Design an experiment to demonstrate hydrotropism.
Answer:
Take two small beakers and label them as A and B. Fill beaker A with water. Now make a cylindrical-shaped roll from a filter paper and keep it as a bridge between beaker A and beaker B, as shown in the figure. Attach a few germinating seeds in the middle of the filter paper bridge. Now, cover the entire set-up with a transparent plastic container so that the moisture is retained.

Observation : The roots of the germinating seeds will grow towards beaker A. This experiment demonstrates the phenomenon of hydrotropism.

Question 34.
Describe the phototropic movement of plants.
Answer:
Movement of plant parts in response to light stimulus is called phototropic movement.

Question 35.
How could you proof that stems are phototropic?
Answer:
If the stem of a plant grows towards the direction of light, then it is called positively phototropic and if the root position grows away from the direction of light, this is negatively phototropic.

Question 36.
What are stimulus and irritability?
Answer:
Stimulus: The change in environmental conditions which produced appreciable effect in plant is called stimulus.
Irritability : The response to stimuli is called Irritability.

Question 37.
What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
Answer:
Functions of receptors :
They sense the external stimuli such as heat or pain.
They also trigger an impulse in the sensory neuron which sends message to the spinal cord.

When the receptors are damaged, the external stimuli transferring signals to the brain are not felt. For example, in the case of damaged receptors, if we accidentally touch any hot object, then our hands might get burnt as damaged receptors cannot perceive the external stimuli of heat and pain.

Long Answer Type Questions : 5 Marks

Question 1.
List the different movements of plant in a tabular form.
Answer:

Question 2.
What do you mean by spontaneous and induced movement?
Answer:
Spontaneous movement : There are plant movements which take place spontaneously without any external stimuli. These movements are described spontaneous or autonomic movements.
Induced movement : Some plant movements are caused in response to certain stimuli and they are said to be induced or plant movement which take place spontaneously, without any irritability and sensitivity of protoplasm.

Question 3.
What do you mean by movement of locomotion?
Answer:
Movements of the whole plant body or of an organ or of material within the plant cell which occur in responses to inherent factors and are free and spontaneous are said to be movements of locomotion. Examples : cyclosis (streaming of protoplasm), oscillatory movements of Oscilatoria, Motility of zoospores.

Question 4.
What do you mean by growth and curvature movement?
Answer:
These movements are brought about by unequal growth on different sides of an organ.
These are of the following types :
A. Nutation : The side of the supporting organ that is in contact of the support grows at a slower rate than the opposite side. This brings about a curvature which helps the supporting organ is spiralling or twinning around the support.

B. Nastic : These movements occur due to differences in the rate of growth on the two opposite surface of a plant organ. When the movement occurs due to faster growth on the upper surface of the organ, it is said to be epinastic movement and when on the lower surface of the growing organ, it is known as hyponastic movement.

Examples : Opening of floral buds and circinately coiled leaves are good examples of nastic movements.

Question 5.
How lateral leaflets move in Indian telegraph plant?
Answer:
These movements occurs due to periodic variations in the turgidity of cells of an organ.
The example is Indian telegraph plant, Desmodium gyrans, where up and down movements of the two lateral leaflets occur in a rhythmic manner.

These leaflets periodically drop down and rise up. This happens due to the presence of large thin walled motor cells at the bases of the leaflets.
When these cells lose water into neighbouring cells, they collapse and the leaflets drop down, and when they regain water, they become turgid and leaflets acquire their upright position.

Question 6.
Describe phototropism with an experiment.
Answer:
These curvature movements occur when a plant is provided with artificial or natural light only from one direction. Stems which generally show a curvature towards the source of light are said to be positively phototropic. Roots which grow away from the source of light are called negatively phototropic.

Question 7.
Describe geotropism with an experiment.
Answer:
Growth movements induced by stimulus of gravity are said to be geotropism. Primary roots always grow downward in the direction of gravity and thus are positively geotropic, whereas the main shoots grow upward away from the gravity and are thus negatively geotropic.

The secondary lateral roots are shoots show a weaker response to gravity and thus take up a position at an angle to the gravitational stimulus and are called diageotropic.
Demostration of geotropism : Geotropism can be demonstrate in the laboratory with the instrument known as Clinostat. It can allow a potted plant fixed on it to rotate at a definite speed.
Two clinostats are taken and a potted plant on each is fixed on a horizontal position.

One clinostat is rotated and the other is kept stationary. Observations made after sometime will show that the shoot of the plant fixed on the stationary clinostat bends upwards showing negative geotropism and the root bends downwards showing positive geotropism. But their is no bending in the root and shoot of the plant fixed on the rotating clinostat. This is due to the fact that gravitational stimulus is not unilateral as it affects the sides of the rotating organs equally.

Negative geotropic response of shoots :

1. Shoots which are negatively geotropic grow vertically and it helps the plant to complete for light and Carbon dioxide.
2. The flowers are brought into an advantageous position for pollination through insects or wind.
3. Seed dispersal may be more effective on long and vertical stem.

Positive geotropic response of roots :

1. It causes roots to grow downwards into the earth where they can anchor the plant firmly in the soil.
2.  It causes them to obtain water and minarals salts.
3. Lateral roots, not positively geotropic grow at right angles or slightly downwards from the main root. This enables a large volume of soil to be exploited and helps to anchor the plants securely.

Question 8.
Explain hydrotropism with an experiment.
Answer:
Growth movements in response to unilateral stimulus of water are known as hydrotropism.
Roots are positively hydrotropic as they bend towards the source of water.

Question 9.
What do mean by phototactic movement?
Answer:
The tactic movements are in response to unidirectional light. Examples : Free swimming algae, zoospores, gametes when swim towards the diffused light are said to be positively phototactic and when they move away from the strong light, they are called negatively phototactic.

Question 10.
What do you mean by nastic movement? Describe different types of nastic movement.
Answer:
The movement can be due to the changes in turgor or changes in growth.
Depending upon the nature of stimuli, these movements are of following types :
(A) Nyctinasty
(B) Chemonasty
(C) Seismonasty
A. Nyctinasty
These movements of plant organs occur in response to day and night and thus are also known as sleep movements.
Photonastic : If this movement when induced by change in light intensity. Examples: Flower of Oxalis, Portulaca, Nicotiana, Oenothera etc.

Thermonastic : This movements is induced by change in temperature intensity. Example : Tulip and Saffron (Crocus)
A temperature rise of only 36 degrees is enough to begin to open a crocus.

B. Chemonasty : This movement occurs in response to some chemical stimulus. eg. Strong chemonasty is exhibited by long peripheral tentacles of sundew leaves(Drosera) which respond to the presence of organic nitrogenous compounds by bending towards the middle of leaf.

C. Seismonasty :
These movements are in response to shock by a touch stimulus. Example : Neptunia, Biophylum, Mimosa pudica, Begonia, Mytinia etc.

Question 11.
Give a brief account of turgor movement shown by Mimosa pudica.
Answer:

• These base of the petiole is swollen (Pulvinus) and similar but smaller pulvinus are present at the base of each leaflet.
• Lower half thin walled and upper half thick walled.
• If the terminal pinnule is struck a blow or touched, the stimulus is conducted to its base and then other pinnules.
• This stimulus causes fall in turgor of lower cells due to loss of water.
• Upper half retains turgidity.
• Turgid half presses flaccid lower half/leaf droops.
• When the touch stimulus is removed regains turgidity.

Question 12.
Difference between nastic and tropic movement?
Answer:
Nastic Movement : Nastic movements are non-directional responses to stimuli (e.g. temperature, Humidity, light, irradiance). The movement can be due to changes in turgor or changes in growth. Nastic movements differ from tropic movements in that the direction of tropic responses depends on the direction of the stimulus, whereas the direction of nastic movement is independent of the stimulus. The rate or frequency of these responses increases as intensity of the stimulus increases. An example of such a response is the opening and closing of flowers (photonastic response). Nastic responses are usually associated with plants.’

Tropism Movement : ‘A tropism (from Greek, tropos, to turn) is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus’. In tropisms, this response is dependent on the direction of the stimulus’ (as opposed to nastic movements which are non-directional responses). Viruses and other pathogens also affect what is called ‘host tropism’ or ‘cell tropism’, in which case tropism refers to species, or specific cell types within those species. The word tropism comes from the Greek trope (‘to turn’ or ‘to change’). Tropisms are usually named for the stimulus involved (for example, a phototropism is a reaction to light) and may be either positive (towards the stimulus) or negative (away from the stimulus).

Multiple Choice Questions : 1 Mark

Question 1.
Tropic movements are
(a) In response to light
(b) In response of gravity
(c) Uni-directional
(d) Non-directional
Answer:
(c) Uni-directional

Question 2.
Stimulus is
(a) A physical force
(b) Energy
(c) Changed environment
(d) None of these
Answer:
(c) Changed environment

Question 3.
Irritability is
(a) Respond to stimulus
(b) Non respond to stimulus
(c) Changes within body
(d) None of these
Answer:
(a) Respond to stimulus

Question 4.
Respond to stimuli in plants is taken by
(a) Nervous system
(b) Growth movement
(c) Hormonal movement
(d) Turgor pressure.
Answer:
(b) Growth movement

Question 5.
Movement of whole plant in response to external stimuli is called
(a) Tropic movement
(b) Tactic movement
(c) Nastism
(d) Hyprotropism
Answer:
(b) Tactic movement

Question 6.
Root always
(a) Moves towards light
(b) Moves towards soil
(c) Moves towards surface of the soil
(d) Showing geotropism
Answer:
(d) Showing geotropism

Question 7.
Stems are always
(a) Geotropic
(b) Phototropic
(c) Hydrotropic
(d) Chemotropic
Answer:
(b) Phototropic

Question 8.
Roots response towards the force of gravity is the display of
(a) Positive geotropism
(b) Negative geotropism
(c) Both of them
(d) None of above
Answer:
(a) Positive geotropism

Question 9.
In hyponasty the bud will remain
(a) Close
(b) Open
(c) Semi-open
(d) Wilt
Answer:
(a) Close

Question 10.
The leaves and petals follow the growth pattern with respect to movement is
(a) Epinasty
(b) Hyponasty
(c) Nutation
(d) None of these
Answer:
(a) Epinasty

Question 11.
If the movement is towards the stimulus the response is
(a) Positive
(b) Negative
(c) No response
(d) None of these
Answer:
(a) Positive

Question 12.
The leaves of mimosa require a specific time to regain its turgidity i.e.
(a) 5 minutes
(b) 10 minutes
(c) 8 minutes
(d) 12 minutes
Answer:
(b) 10 minutes

Question 13.
Movement of leaves of sensitive plant, Mimosa pudica are due to
(a) Thermonasty
(b) Seismonasty
(c) Hydrotropism
(d) Chemonasty
Answer:
(b) Seismonasty

Question 14.
Twinning of tendrils is due to
(a) Thigmotropism
(b) Seismonasty
(c) Heliotropism
(d) Diageotropism
Answer:
(a) Thigmotropism

Question 15.
Removal of apical bud results in
(a) formation of new apical bud
(b) elongation of main stem
(c) death of plant
(d) formation of lateral branching
Answer:
(d) formation of lateral branching

Question 16.
The closure of lid of pitcher in pitcher plant, is due to
(a) parotomic movement
(b) autonomous movement
(c) turgor movement
(d) tropic movement
Answer:
(a) parotomic movement

Question 17.
The twinning of tendrils around a support is a good example of
(a) phototropism
(b) chemotropism
(c) nastic movements
(d) thigmotropism
Answer:
(d) thigmotropism

Question 18.
If a tree flowers thrice in a year (Oct., Jan. and July) in Northern India, it is said to be
(a) photo and thermo-insensitive
(b) photo and thermo-sensitive
(c) photosensitive but thermo-insensitive
(d) thermosensitive but photo-insensitive
Answer:
(a) photo and thermo-insensitive

Question 19.
The closing and opening of the leaves of Mimosa pudica is due to
(a) seismonastic movement
(b) chemonastic movement
(c) thermonastic movement
(d) hydrotropic movement
Answer:
(a) seismonastic movement

Question 20.
The ability of the Venus Flytrap to capture insects is due to
(a) Specialized “muscle-like” cells
(b) Chemical stimulation by the prey
(c) a passive process requiring no special ability on the part of the plant
(d) rapid turgor pressure changes.
Answer:
(d) rapid turgor pressure changes.

Question 21.
Opening of floral buds into flowers is a type of
(a) autonomic movement of variation
(b) paratonic movement of growth
(c) autonomic movement of growth
(d) autonomic movement of locomotion.
Answer:
(c) autonomic movement of growth

Very Short Answer Type Questions : 1 Mark

Question 1.
Stimulus is __________.
Answer:
Energy.

Question 2.
Irritability is __________.
Answer:
Respond to stimulus

Question 3.
Respond to stimuli in plants is taken by __________.
Answer:
Growth movement

Question 4.
Movement of whole plant in response to external stimuli is called __________.
Answer:
Tactic Movement

Question 5.
Root always __________.
Answer:
Showing Geotropism

Question 6.
Stems are always __________.
Answer:
Geotropic

Question 7.
Give one eg. of seismonastic movement in Plant.
Answer:
Mimosa pudica

Question 8.
Name the secondary plant organs where transversely geotropic movement is found.
Answer:
Rhizomes

Question 9.
Write the types of tropic movement.
Answer:

• Phototropic movement
• Geotropic movement
• Hydrotropic movement

Question 10.
Flowers of Tulip shows what type of nastic movement?
Answer:
Thermonastic movement.

Question 11.
The Plant movement away from light is also called __________.
Answer:
Geotropism.

Question 12.
The ‘Touch me not’ plant exhibits __________.
Answer:
Seismonastic movement.

Question 13.
A free swimming alga.
Answer:
Chlamydomonas.

Question 14.
Clinostat demonstrates __________.
Answer:
Geotropism

Question 15.
Stem bends towards light, what type of movement it is ?
Answer:
Phototropic movement.

Question 16.
When a sensitive plant is touched, it drops its leaves. What type of movement it is?
Answer:
Seismonastic movement.

Question 17.
Who discovered the sensitivity of plant?
Answer:
J.C. Bose.

Question 18.
Which type of movement show in volvox?
Answer:
Phototropic.

Question 19.
Chemonastic movement is found in __________.
Answer:
Desmodium

Question 20.
Which type of movement found in Tulip?
Answer:
Thermonastic.

Question 21.
What is the name of Indian Telegraph plant?
Answer:
Desmodium.

Question 22.
Which movement is exhibited by Mimosa pudica?
Answer:
Seismonastic movement.

Question 23.
What is response to a stimuli?
Answer:
Responding to a stimulus is the faculty of sensitivity.