The only phytohormone which is a gas at ordinary temperature:
- Ethane
- Ethyl alcohol
- Ethylene
- Ethyne
Answer
Ethylene
Reason — Ethylene is the only hormone which is gas at ordinary temperature.
The hormone which promotes the ripening of fruits is:
- Auxins
- Gibberellins
- Cytokinins
- Ethylene
Answer
Ethylene
Reason — Ethylene helps in natural as well as artificial ripening of fruits.
A growth inhibiting hormone in plants:
- Gibberellins
- Indole-3 acetic acid
- Abscisic Acid
- Cytokinins
Answer
Abscisic Acid
Reason — Abscisic Acid acts as growth inhibitor by slowing down plant metabolism.
The hormone which stimulates cell division:
- Auxins
- Cytokinins
- Gibberellins
- Abscisic acid
Answer
Cytokinins
Reason — Cytokinins stimulate plant growth by promoting cell division. They are present in large amount in germinating seeds and developing fruits.
Development of fruits without fertilization is called:
- Parthenogenesis
- Parthenon
- Parthenocarpy
- Dormancy
Answer
Parthenocarpy
Reason — Development of fruits without fertilization is called Parthenocarpy. It can be induced by auxins.
The response by parts of the plant towards stimulus is called as:
- Nastic movement
- Tropism
- Tactic movement
- Senescence
Answer
Tropism
Reason — Growth movements occurring in response to unidirectional external stimuli in a plant part is called tropic movements.
Apical dominance is influenced by :
- Gibberellins
- Ethylene
- Cytokinins
- Auxins
Answer
Auxins
Reason — The phenomenon of the suppression of growth of lateral buds by apical buds is called apical dominance and it is seen due to presence of auxin in apex region of plant.
The growth movement of plant parts which occurs due to touch stimulus is called:
- Heliotropism
- Chemotropism
- Hydrotropism
- Thigmotropism
Answer
Thigmotropism
Reason — The growth movement of plant parts which occurs due to touch stimulus is called thigmotropism. For example, coiling of tendrils to their support.
The instrument which can be used to demonstrate geotropism is:
- Manometer
- Thermostat
- Clinostat
- Barometer
Answer
Clinostat
Reason — Geotropism can be demonstrated in laboratory by using Clinostat. It has two set-ups with planted pots. One is static while the other rotates.
The hormone which accelerates senescence (ageing) and abscission of leaves is :
- IAA
- GA3
- ABA
- GA1
Answer
ABA
Reason — Abscisic Acid (ABA) is the hormone which accelerates senescence (ageing) and abscission of leaves. It is a growth inhibitor.
Match the items in column A with those of column B.
| Column A | Column B |
|---|---|
| (a) Auxin | (i) apical dominance |
| (b) Gibberellin | (ii) cell-division |
| (c) Cytokinin | (iii) fruit ripening |
| (d) Ethylene | (iv) internodal elongation |
Answer
| Column A | Column B |
|---|---|
| (a) Auxin | (i) apical dominance |
| (b) Gibberellin | (iv) internodal elongation |
| (c) Cytokinin | (ii) cell division |
| (d) Ethylene | (iii) fruit ripening |
Complete the following sentences:
(a) Growth of root towards water is ............... .
(b) ............... hormone inhibits apical dominance.
(c) ............... and ............... induce chemotropism of angiosperms and gymnosperms.
(d) ............... of sweet peas exhibit thigmotropism.
(e) ............... is also called as "stress hormone".
Answer
(a) Growth of root towards water is hydrotropism .
(b) Cytokinins hormone inhibits apical dominance.
(c) Sugars and peptones induce chemotropism of angiosperms and gymnosperms.
(d) Tendrils of sweet peas exhibit thigmotropism.
(e) Abscisic acid is also called as "stress hormone".
How is movement in plants different from that in animals?
Answer
Differences between movement in plants and movement in animals are as follows —
| Movement in plants | Movement in animals |
|---|---|
| Plant movements are often related to growth. | Animal movements are not related to growth. |
| Plant movements are confined to only some plant parts. | Animal movements involve movement of the entire body. |
| No muscles are involved in plant movements. | Muscles are involved in animal movements. |
| It involves bending, twisting and elongation of plant parts. | It involves displacement from one place to another. |
| Movement is said to be non-locomotory. | Movement is said to be locomotory. |
| Plants generally move to secure support, capture food or to find water or soil nutrients. | Animals generally move to find mates, for protection from environmental changes and to capture food. |
Name the stimulus which causes the following movements in plants: phototropism, thigmotropism, hydrotropism and geotropism.
Answer
- Phototropism → Light
- Thigmotropism → Touch
- Hydrotropism → Water
- Geotropism → Gravity
Name the following.
(a) A hormone that stimulates growth by cell division.
(b) A growth-retarding hormone in plants.
(c) The main auxin found in most plants.
Answer
(a) Cytokinin
(b) Abscisic acid
(c) Indole 3-acetic acid (IAA)
Define the following terms:
(a) Phytohormones
(b) Tropism
(c) Clinostat
(d) Apical dominance
(e) Parthenocarpy
(f) Abscission
(g) Heliotropism
Answer
(a) Phytohormones — Phytohormones or plant hormones are naturally occurring small organic molecules.
(b) Tropism — Response or orientation of a plant to certain stimulus that acts with greater intensity from one direction to another is called tropism.
(c) Clinostat — Clinostat is a mechanical device that rotates at a slow speed to demonstrate geotropism.
(d) Apical dominance — The phenomenon of the suppression of growth of lateral buds by apical buds is called apical dominance.
(e) Parthenocarpy — Development of fruits without fertilisation is called parthenocarpy.
(f) Abscission — Abscission is the shedding of various parts of a plant such as leaves, buds, flowers and fruits.
(g) Heliotropism — The phenomenon in which the young flower heads follow the sun across the sky as it moves from east to west direction is called heliotropism.
List five plant growth hormones and mention one important role of each.
Answer
- Auxins — Auxins promote the growth of stem, roots and fruits by cell elongation.
- Gibberellins — Gibberellins promote the growth of internodes by cell elongation.
- Cytokinins — Cytokinins stimulate cell division.
- Ethylene — Ethylene helps in ripening of fruits.
- Abscisic acid — Abscisic acid induces dormancy of buds and seeds.
Differentiate between:
(a) Thigmotropism and geotropism
(b) Positive and negative tropism
(c) Stimulus and response
(d) Phototropism and chemotropism
Answer
(a) Difference between thigmotropism and geotropism
| Thigmotropism | Geotropism |
|---|---|
| Directional growth movement of a plant part in response to the touch of an object. | Directional growth movement of a plant part in response to gravity. |
| Example — Plants such as sweet peas, Cuscuta and vines have tendrils which coil around other plants in response to one sided contact or touch. | Example — Growth of roots of plants in downward direction. |
(b) Difference between positive and negative tropism
| Positive tropism | Negative tropism |
|---|---|
| Movement of plant part towards the direction of the stimulus is called positive tropism. | Movement of plant part against the direction of the stimulus is called negative tropism. |
| Example — Shoots show positive phototropism and grow in the direction of sunlight. | Example — Roots show negative phototropism and grow against the direction of sunlight. |
(c) Difference between stimulus and response
| Stimulus | Response |
|---|---|
| Change in the internal or external environment of an organism is called a stimulus. | Resulting action or movement caused by the stimulus is called a response. |
| Example — In phototropism, sunlight is the stimulus. | Example — In phototropism, the bending of the shoot is the response to the stimulus of sunlight. |
(d) Difference between phototropism and chemotropism
| Phototropism | Chemotropism |
|---|---|
| It means the movement in response to the stimulus of light. | It is the phenomenon of growth or movement of a plant part towards the source of nutrients or chemicals. |
| Example — Growth of shoots of plants in upward direction. | Example — Growth of pollen tube towards sugar and peptones of the female gametophyte. |
The tea plants are never allowed to grow lengthwise. This is done by cutting their apical buds, a process known as pruning. In this way, tea plants get a dense growth and easy yield. Answer the following questions:
(a) Name the scientific phenomenon that is being overcome by pruning.
(b) What plant hormone is responsible for the scientific phenomenon mentioned in (a).
(c) Name one plant hormone which inhibits the said phenomenon.
Answer
(a) Apical dominance
(b) Auxins
(c) Cytokinins
The figure given below shows the stages of ripening in a banana. Answer the questions that follow:
(a) Name the plant hormone responsible for the above changes.
(b) Mention two characteristic features of this hormone.
Answer
(a) The plant hormone responsible for the above changes is Ethylene. It is the only hormone which is a gas at ordinary temperature. It is produced in fruits and remain in the same fruit.
(b) Characteristic features of ethylene are:
- It is synthesised in flowers, germinating seeds and ripening fruits.
- It promotes root growth and root hair formation and also induces and promotes fruit ripening.
The diagram given alongside shows a type of tropism. Study the same and answer the questions that follow:
(a) Name and define the type of tropism shown in the diagram.
(b) Label the guidelines (1) to (4).
(c) Name two effective stimulants that help in the growth of part (2).
(d) Name two groups of plants where part (2) grows towards gametophyte with the help of the stimulants mentioned in (c).
Answer
(a) The type of tropism shown in the diagram is Chemotropism. It is the phenomenon of growth of plant organs in response to chemicals.
(b) Guidelines (1) to (4) are labelled below:
- 1 → Pollen grain
- 2 → Pollen tube
- 3 → Ovule
- 4 → Ovary
(c) Sugars and peptones.
(d) Gymnosperms and angiosperms.
Study the diagrams given below and answer the following questions.
(a) Name the structures shown as X and Y in the figures (A) and (B), respectively.
(b) Write the functions performed by the structures X and Y.
(c) Name the phenomenon depicted and define it.
(d) How do the structures X and Y differ from each other?
(e) Give examples of the plants which show the said phenomenon.
Answer
(a) X → Stem tendrils, Y → Leaf tendrils.
(b) Stem tendrils (X) and leaf tendrils (Y) enable the plant to climb up a support.
(c) Thigmotropism is the phenomenon depicted. It is the growth movement of plant parts in response to touch stimulus.
(d) Stem tendrils (X) arise from the stem while leaf tendrils (Y) arise from the leaf of the plant.
(e) Sweet Pea, Vines and Cuscuta.
Given below are the figures showing some kinds of tropic movements in plants. Study the same and answer the following questions:
(a) Which one of these figures is correct? Give reason in support of your answer.
(b) Name the kind of movements shown by the root system and the shoot system. Define each.
(c) What are the two stimuli which affect root system and shoot system? Name them.
(d) Which of the following stimuli affect the growth of root strongly?
- Gravity
- Water
(e) Draw a neat and labelled diagram of the longitudinal section of a pistil showing chemotropism in an angiospermic plant.
Answer
(a) Figure A is correct as it shows roots growing towards gravity and shoot growing away from gravity.
(b) Root shows positive geotropism and shoot shows negative geotropism.
Positive geotropism is defined as movement of plant towards earth's gravity. For example, roots show positive geotropism.
Negative geotropism is defined as movement of plant away from gravity. For example, shoot shows negative geotropism.
(c) Root system — Gravity
Shoot system — Light
(d) Gravity
(e) Below diagram shows chemotropism in a pistil:
The box given below contains twelve words. Out of these, ten can be arranged in five suitable matching pairs. Make these five pairs in the form of a table.
| Auxin, Abscisic acid, Fruit ripening, Cytokinins, Closure of stomata, Parthenocarpy, Ethylene, Gibberellins, Tropism, Stem elongation, Cuscuta, Cell division |
Answer
| Plant Hormone | Function |
|---|---|
| Auxin | Parthenocarpy |
| Abscisic Acid | Closure of stomata |
| Cytokinins | Cell division |
| Ethylene | Fruit Ripening |
| Gibberellins | Stem elongation |
The figure given below depicts a kind of tropic movement in plants. Study the same and answer the following questions.
(a) What kind of a movement is shown in figure. Define it.
(b) How does this movement differ from geotropism?
(c) Name the stimulus responsible for thigmotropism. Give one example of a plant showing thigmotropism.
(d) Name one stimulus which gives a positive response for the roots but negative response for the shoot.
(e) Draw a neat and labelled diagram of the part of plant showing leaf tendril. Name the plant.
Answer
(a) Phototropism.
It is defined as the movement in response to the stimulus of light.
(b) Stimulus for phototropism is light whereas for geotropism it is gravity.
(c) Touch is the stimulus for thigmotropism.
Example — The tendrils of sweet pea plant start coiling around the support in response to touch.
(d) Gravity
(e) Sweet pea plant shows thigmotropism. The labelled diagram showing leaf tendril is given below:
