Chapter 7 : Chemical Coordination in Plants - Selina Solutions for Class 10 Biology ICSE

Biology is one of the crucial subjects in ICSE Class 10. ICSE Class 10 Biology speaks about the cell as the basic unit of life, genes, and evolution and deals with how living organisms interact with the environment, including the behavior of living beings. TopperLearning is one of the premier online platforms which helps students of ICSE Class 10 to study various concepts in Biology.

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Chapter 7 - Chemical Coordination in Plants Excercise Ex. 1

Question 1

A plant hormone related with inhibition of senescence is

(a) Ethylene

(b) ABA

(c) Bromic acid

(d) GA

Solution 1

(d) GA

Question 2

Apical dominance phenomenon is caused by

(a) Auxins

(b) GA

(c) Cytokinins

(d) ABA

Solution 2

(a) Auxins

Question 3

Which of the following hormones regulate stomatal colour?

(a) Auxins

(b) GA

(c) ABA

(d) Cytokinins

Solution 3

(d) Cytokinins

Question 4

Auxins are abundantly produced in

(a) base of the root

(b) base of the shoot

(c) shoot

(d) meristematic region of the shoot

Solution 4

(d) meristematic region of the shoot

Question 5

A higher concentration of ethylene is found in

(a) green banana

(b) ripe banana

(c) fresh potato tuber

(d) green apple

Solution 5

(b) ripe banana

Question 6

Common gibberellin is

(a) GA1

(b) GA2

(c) GA3

(d) GA7

Solution 6

(c) GA3

Question 7

Stems are

(a) positively geotropic and negatively phototropic

(b) positively geotropic and positively phototropic

(c) negatively geotropic and positively phototropic

(d) negatively phototropic and negatively geotropic

Solution 7

(c) negatively geotropic and positively phototropic

Question 8

In tropic movements, plant parts move

(a) away from the stimulus

(b) towards the stimulus

(c) either towards or away from the stimulus

(d) only towards water

Solution 8

(c) either towards or away from the stimulus

Question 9

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

 

Solution 9

Column A

Column B

(a) Auxin

(i) apical dominance

(b) Gibberellin

(iv) internodal elongation

(c) Cytokinin

(ii) cell division

(d) Ethylene

(iii) fruit ripening

 

Question 10

Differentiate between:

(a) Thigmotropism and geotropism

(b) Phototropism and chemotropism

Solution 10

(a) Differences 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: Coiling of tendrils around support
  • Example: Growth of roots of plants in downward direction

 

 

(b) Differences between phototropism and chemotropism:

Phototropism

Chemotropism

  • Directional growth movement of a plant part in response to light
  • Directional growth movement of a plant part in response to chemicals
  • Example: Growth of shoots of plants in upward direction
  • Example: Growth of pollen tube towards female gametophyte

 

Question 11

How is movement in plants different from that in animals?

Solution 11

Differences between movement in plants and movement in animals:

Movement in plants

Movement in animals

 

  • 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 non-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.

 

  • Plant movements are confined to only some plant parts.

 

  • Animal movements involve movement of the entire body. 

 

  • Plant movements are often related to growth.

 

  • Animal movements are not related to growth.

 

  • No muscles are involved in plant movements.

 

  • Muscles are involved in animal movements.
Question 12

Name the stimulus which causes the following movements in plants.

phototropism, thigmotropism, hydrotropism and geotropism

Solution 12

Tropic movement

Stimulus

Phototropism

Light

Thigmotropism 

Touch

Hydrotropism

Water

Geotropism

Gravity

 

Question 13

Name the following.

(a) Hormone that stimulates growth by cell division.

(b) Growth retarding hormone in plants.

(c) Main auxin found in most plants.

Solution 13

(a) Cytokinin

(b) Abscisic acid

(c) Indole 3-acetic acid (IAA)

Question 14

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

Solution 14

The directional movement of plant parts towards or away from a stimulus is known as tropic movement or tropism.

Different types of tropic movements in plants:

Tropic Movement

Description

Phototropism 

 

  • Movement of plant parts towards or away from light is termed phototropism.
  • Because 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.

 

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, i.e. against gravity, and hence is negatively geotropic.

Chemotropism 

 

  • Movement of plant organs in response to a chemical stimulus is called chemotropism.
  • 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.

Hydrotropism 

 

  • Movement of plant organs in response to water is termed hydrotropism.
  • Roots grow towards the source of moisture and hence are positively hydrotropic.

Thigmotropism 

 

  • Movement of plant organs in response to stimuli caused by physical contact with solid objects is termed thigmotropism.
  • 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 15

List five plant growth hormones and briefly describe their roles.

Solution 15

Plant growth hormones and their roles:

Plant growth hormones

Roles

Auxins 

  • Promote elongation and the growth of stems and roots
  • Promote cell division in vascular cambium
  • Auxins of the apical bud inhibit the growth of lateral buds (apical dominance)

Cytokinins 

  • Stimulate cell division and prevent the onset of senescence in tissues
  • Stimulate cell division
  • Break dormancy of seeds
  • Delay senescence of leaves and other organs
  • Promote growth of lateral buds

Gibberellins

  • Enhance the longitudinal growth of the stem
  • Cause stem elongation and leaf expansion but have no effect on roots
  • Break dormancy of buds and tubers
  • Cause delay in senescence
  • Promote elongation of internodes in sugarcane

 

Ethylene

  • Inhibits the growth of lateral buds and causes apical dominance
  • Breaks the dormancy of buds and seeds
  • Associated with the process of ageing of plant organs such as yellowing of leaves

Abscisic acid

  • Induces dormancy in buds, stems and seeds
  • Induces and maintains dormancy in many seeds
  • Inhibits flowering in short-day plants
  • Inhibits cell division and cell elongation

 

Question 16

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

Solution 16

The response of plants to gravity can be observed in the laboratory when the seedlings are placed in a pot filled with moist soil.

  

 

Roots of plants show positive geotropism which means that they grow in the direction of gravity in the downward direction. This movement is good for the growth of the seedling. The roots need to grow downwards in the soil in search of water and minerals.

 

Shoots of plants show negative geotropism which means that they grow against the direction of gravity in the upward direction. This movement is beneficial for the elongation of the plant. The shoots need to grow upwards in the direction of sunlight so that the plant can grow in height.

Question 17

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

Solution 17

Positive tropic movements in plants:

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

Examples:

 Growth of shoots towards light

 Growth of roots towards gravity

 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:

 Growth of roots away from light

 Growth of shoots upwards and away from gravity

 Growth of shoots away from water

Question 18

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

Solution 18

Aim:

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.

Question 19

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.

Solution 19

(a) Apical dominance

(b) Auxins

(c) Cytokinins

Question 20

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.

Solution 20

(a) Ethylene

(b) Characteristic features of ethylene:

 Site of synthesis:

o It is synthesised in senescent leaves and flowers, germinating seeds and ripening fruits.

 Functions:

o Induces and promotes fruit ripening

o Promotes fruit ripening

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