SELINA Solutions for Class 10 Biology Chapter 7 - Chemical Coordination in Plants

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Chapter 7 - Chemical Coordination in Plants Exercise Ex. 1

Question A.1

A plant hormone related with inhibition of senescence is

(a) Ethylene

(b) ABA

(c) Bromic acid

(d) GA

Solution A.1

(d) GA

Question A.2

Apical dominance phenomenon is caused by

(a) Auxins

(b) GA

(c) Cytokinins

(d) ABA

Solution A.2

(a) Auxins

Question A.3

Which of the following hormones regulate stomatal colour?

(a) Auxins

(b) GA

(c) ABA

(d) Cytokinins

Solution A.3

(d) Cytokinins

Question A.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 A.4

(d) meristematic region of the shoot

Question A.5

A higher concentration of ethylene is found in

(a) green banana

(b) ripe banana

(c) fresh potato tuber

(d) green apple

Solution A.5

(b) ripe banana

Question A.6

Common gibberellin is

(a) GA1

(b) GA2

(c) GA3

(d) GA7

Solution A.6

(c) GA3

Question A.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 A.7

(c) negatively geotropic and positively phototropic

Question A.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 A.8

(c) either towards or away from the stimulus

Question B.1

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 B.1

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 B.2

Differentiate between:

(a) Thigmotropism and geotropism

(b) Positive and negative tropism

(c) Stimulus and response

(d) Phototropism and chemotropism

Solution B.2

(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 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) Differences 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) 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 B.3

How is movement in plants different from that in animals?

Solution B.3

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 B.4

Name the stimulus which causes the following movements in plants.

phototropism, thigmotropism, hydrotropism and geotropism

Solution B.4

Tropic movement

Stimulus

Phototropism

Light

Thigmotropism 

Touch

Hydrotropism

Water

Geotropism

Gravity

 

Question B.5

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 B.5

(a) Cytokinin

(b) Abscisic acid

(c) Indole 3-acetic acid (IAA)

Question C.1

Define the following terms:

(a) Phytohormones

(b) Tropism

(c) Clinostat

(d) Apical dominance

(e) Parthenocarpy

(f) Abscission

(g) Heliotropism

Solution C.1

(a) Phytohormones: Hormones in plants are called phytohormones.

 

(b) Tropism: Movements in plants in which the direction of the response is related to the direction from which the stimulus comes is called tropism.

 

(c) Clinostat: Clinostat is an instrument which can allow a potted plant to rotate 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 falling off or shedding of various plant parts 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 C.2

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

Solution C.2

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 C.3

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

Solution C.3

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 C.4

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

Solution C.4

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 C.5

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

Solution C.5

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.

 

Selina Solutions Icse Class 10 Biology Chapter - Chemical Coordination In Plants 

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 D.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.

Solution D.1

(a) Apical dominance

(b) Auxins

(c) Cytokinins

Question D.2

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

Selina Solutions Icse Class 10 Biology Chapter - Chemical Coordination In Plants 

(a) Name the plant hormone responsible for the above changes.

(b) Mention two characteristic features of this hormone.

Solution D.2

(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

Question D.3

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

Selina Solutions Icse Class 10 Biology Chapter - Chemical Coordination In Plants 

(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).

Solution D.3

(a) Chemotropism. It is the phenomenon of growth of plant organs in response to chemicals.

 

(b) (1): Pollen grain, (2): Pollen tube, (3): Ovule, (4): Ovary.

 

(c) Sugars and peptones.

 

(d) Gymnosperms and angiosperms.

Question D.4

Study the diagrams given below and answer the following questions:

Selina Solutions Icse Class 10 Biology Chapter - Chemical Coordination In Plants 

(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.

Solution D.4

(a) X: Stem tendrils, Y: Leaf tendrils.

 

(b) Functions of X and Y: Stem and leaf tendrils enable the plant to climb up a support.

 

(c) Thigmotropism. 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.