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Chapter 7

Chemical Coordination in Plants

Class 10 - Selina Concise Biology Solutions


Multiple Choice Type

(Select the most appropriate option in each case)

Question 1

A plant hormone related with inhibition of senescence is

  1. Ethylene
  2. ABA
  3. Bromic acid
  4. GA ✓

Question 2

Apical dominance phenomenon is caused by

  1. Auxins ✓
  2. GA
  3. Cytokinins
  4. ABA

Question 3

Which of the following hormones regulate stomatal closure?

  1. Auxins
  2. GA
  3. ABA ✓
  4. Cytokinin

Question 4

Auxins are abundantly produced in

  1. base of the root
  2. base of the shoot
  3. shoot
  4. meristematic region of the shoot ✓

Question 5

A higher concentration of ethylene is found in

  1. green banana
  2. ripe banana ✓
  3. fresh potato tuber
  4. green apple

Question 6

Common gibberellin is

  1. GA1
  2. GA2
  3. GA3 ✓
  4. GA7

Question 7

Stems are

  1. positively geotropic and negatively phototropic
  2. positively geotropic and positively phototropic
  3. negatively geotropic and positively phototropic ✓
  4. negatively phototropic and negatively geotropic

Question 8

In tropic movements, plant parts move

  1. away from the stimulus
  2. towards the stimulus
  3. either towards or away from the stimulus ✓
  4. only towards water

Short Answer Type

Question 1

Match the items in column A with those of column B.

Column AColumn B
(a) Auxin(i) apical dominance
(b) Gibberellin(ii) cell-division
(c) Cytokinin(iii) fruit ripening
(d) Ethylene(iv) internodal elongation

Answer

Column AColumn B
(a) Auxin(i) apical dominance
(b) Gibberellin(iv) internodal elongation
(c) Cytokinin(ii) cell division
(d) Ethylene(iii) fruit ripening

Question 2

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

ThigmotropismGeotropism
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 tropismNegative 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

StimulusResponse
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

PhototropismChemotropism
It means movement towards light.It is the phenomenon of growth of plant organs in response to chemicals.
Example — Growth of shoots of plants in upward direction.Example — Growth of pollen tube towards female gametophyte.

Question 3

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 plantsMovement 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.

Question 4

Name the stimulus which causes the following movements in plants: phototropism, thigmotropism, hydrotropism and geotropism.

Answer

  • Phototropism → Light
  • Thigmotropism → Touch
  • Hydrotropism → Water
  • Geotropism → Gravity

Question 5

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)

Descriptive Type

Question 1

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.

Question 2

List five plant growth hormones and mention one important role of each.

Answer

  1. Auxins — Auxins promote the growth of stem, roots and fruits by cell elongation.
  2. Gibberellins — Gibberellins promote the growth of internodes by cell elongation.
  3. Cytokinins — Cytokinins stimulate cell division.
  4. Ethylene — Ethylene helps in ripening of fruits.
  5. Abscisic acid — Abscisic acid induces dormancy of buds and seeds.

Question 3

What are tropic movements? Briefly explain various types of tropic movements in plants.

Answer

Growth movements occurring in response to unidirectional external stimuli in a plant part are known as tropic movement or tropism.

Different types of tropic movements in plants are:

  1. Phototropism — Movement of plant parts towards or away from light is termed phototropism. The plants grown in light illuminating them from all directions grow more or less upwards. Shoots of most plants grow towards the source of light, it is termed positive phototropism. Roots grow away from light and hence are negatively phototropic.
  2. Geotropism — Movement of plant organs in response to gravity is termed geotropism. Roots are positively geotropic because they grow in the direction of gravity. The shoot grows upwards, means against gravity, and hence is negatively geotropic.
  3. Chemotropism — Chemotropism is the phenomenon of growth of plant organs in response to chemicals. When plant organs grow away from the chemical response, it is called negative chemotropism. When plant parts grow towards the chemical response, it is called positive chemotropism. The pollen tube grows towards the sugary substance secreted by the stigma of the flower.
  4. Hydrotropism — Movement of plant organs in response to water is termed hydrotropism. Roots grow towards the source of moisture and hence are positively hydrotropic.
  5. Thigmotropism — The growth movement of plant parts in response to touch stimulus is called thigmotropism. Plants such as sweet peas and vines have tendrils which coil around other plants in response to one sided contact or touch. Stimulus is perceived by tendril tips and then it is transmitted to basal parts. Weak-stemmed plants use twining stems and tendrils to climb on other plants/objects which provide them support. Hence, twining stems and tendrils are positively thigmotropic.

Question 4

The response of plants to gravity is known as geotropism. How are plant parts sensitive to gravity? Describe with the help of a diagram.

Answer

If we sow some seeds of beans or gram in moist soil in glass beaker, they will sprout in 3-4 days. Each seed will give rise to a tiny seedling. Water the seedlings regularly. After 8-9 days of growth, we will observe that the stem has increased in length growing away from the force of gravity whereas the roots have also increased in length but growing towards the force of gravity. The growth in stem shows negative (away) response to gravity, while the root shows positive (towards) response to gravity. The below diagrams shows this growth of seedlings:

The response of plants to gravity is known as geotropism. How are plant parts sensitive to gravity? Describe with the help of a diagram. Chemical Coordination in Plants, Concise Biology Solutions ICSE Class 10.

Question 5

What is meant by positive and negative tropic movements in plants? Explain them by giving suitable examples.

Answer

Positive tropic movements in plants:

Directional movement of a plant part towards the stimulus is called positive tropic movement.

Examples:

  1. Growth of shoots towards light.

  2. Growth of roots towards gravity.

  3. Growth of roots towards water.

Negative tropic movements in plants:

Directional movement of a plant part away from the stimulus is called negative tropic movement.

Examples:

  1. Growth of roots away from light.

  2. Growth of shoots upwards and away from gravity.

  3. Growth of shoots away from water.

Question 6

With the help of an experiment, prove that roots are more positively hydrotropic than geotropic.

Answer

Experiment to prove that roots are more positively hydrotropic than geotropic:

Apparatus:

Wire netting or gauze, wires, moist sawdust, germinating bean seeds.

Procedure:

Take a piece of wire netting or gauze and suspend it with the help of wires. Place moist sawdust of about 1 inch on the wire netting. Embed some germinating bean seeds in the sawdust.

Observation:

As the seeds germinate, the radicles initially grow downwards through the wire netting under the influence of gravity. However, after some time they start growing upwards towards the moist sawdust. The shoots grow upwards all the time.

Inference:

Roots grow in the direction of gravity and water. The growth of roots towards water and overcoming the force of gravity suggests that roots are positively hydrotropic than geotropic. This implies that water is a more effective stimulus than gravity.

With the help of an experiment, prove that roots are more positively hydrotropic than geotropic. Chemical Coordination in Plants, Concise Biology Solutions ICSE Class 10.

Structured / Application / Skill Type

Question 1

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

Question 2

The figure given below shows the stages of ripening in a banana. Answer the questions that follow:

The figure shows the stages of ripening in a banana. Answer the questions that follow. Name the plant hormone responsible for the above changes. Mention two characteristic features of this hormone. Chemical Coordination in Plants, Concise Biology Solutions ICSE Class 10.

(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:

  1. It is synthesised in flowers, germinating seeds and ripening fruits.
  2. It promotes root growth and root hair formation and also induces and promotes fruit ripening.

Question 3

The diagram given alongside shows a type of tropism. Study the same and answer the questions that follow:

The diagram given alongside shows a type of tropism. Study the same and answer the questions that follow. Name and define the type of tropism shown in the diagram. Label the guidelines (1) to (4). Name two effective stimulants that help in the growth of part (2). Name two groups of plants where part (2) grows towards gametophyte with the help of the stimulants mentioned in (c). Chemical Coordination in Plants, Concise Biology Solutions ICSE Class 10.

(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.

Question 4

Study the diagrams given below and answer the following questions.

Study the diagrams given below and answer the following questions. Name the structures shown as X and Y in the figures (A) and (B), respectively. Write the functions performed by the structures X and Y. Name the phenomenon depicted and define it. How do the structures X and Y differ from each other? Give examples of the plants which show the said phenomenon. Chemical Coordination in Plants, Concise Biology Solutions ICSE Class 10.

(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.

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