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

Chemical Coordination in Plants Exercise Ex. 1

Solution A.1

(c) Ethylene

Solution A.2

(d) Ethylene

Solution A.3

(c) Abscisic acid

Solution A.4

(b) Cytokinins 

Solution A.5

(c) Parthenocarpy 

Solution A.6

(b) Tropism 

Solution A.7

(d) Auxins

Solution A.8

(d) Thigmotropism

Solution A.9

(c) Clinostat

Solution A.10

(c) ABA

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


Solution B.2

(a) Growth of root towards water is hydrotropism.

(b) Cytokinin 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".

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.

Solution B.4

Tropic movement











Solution B.5

(a) Cytokinin

(b) Abscisic acid

(c) Indole 3-acetic acid (IAA)

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.

Solution C.2

Plant growth hormones and their roles:

Plant growth hormones



  • 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)


  • 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


  • 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



  • 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


Solution C.3

(a) Differences between thigmotropism and geotropism:



The growth movement of plant parts in response to touch stimulus is called thigmotropism.

The growth movement of plant parts towards gravity is called geotropism.

Example - Coiling of tendrils in sweet peas.

Example- Growth of roots of plants in a downward direction.

(b) Differences between positive tropism and negative tropism:

Positive tropism

Negative tropism

The movement of a plant part in the direction of the stimulus is called positive tropism.

The movement of a plant part in the opposite direction of the stimulus is called negative tropism.

Example- Movement of shoots towards sunlight is positive phototropism.

Example- Movement of roots away from sunlight is negative tropism.

(c) Differences between stimulus and response:



Changes in the internal or external environment of an organism are called stimuli.

The resulting actions or movements caused by the stimuli are called responses.

Example - Light, gravity and seasonal changes.

Example - Bending of shoots, coiling of tendrils.

(d) Differences between phototropism and chemotropism:



The growth movement of plant parts in the direction of light is called phototropism.

The growth movement of plant parts in response to chemicals is called chemotropism.

Example- Growth of shoots of plants towards light.

Example- Growth of pollen-tube towards female gametophyte.


Solution D.1

(a) Apical dominance

(b) Auxins

(c) Cytokinins

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.


o Induces and promotes fruit ripening

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.

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.

Solution D.5

(a) Figure A is correct. The roots always move towards the ground in search of water and minerals. The stem always grows upwards in the direction of sunlight.

(b) The root system shows geotropism. Movement of plant parts towards earth's gravity is called geotropism. The shoot system shows phototropism. Movement of plant parts in the direction of light is called phototropism.

(c) Gravity affects root system positively and the response exhibited by the roots is called positive geotropism. Sunlight affects the shoot system positively and the response exhibited by the shoots is called positive phototropism.

(d) Roots of some plants grow towards source of water, but gravity has an independent and much stronger effect on the direction of root growth.

(e) Longitudinal section of a pistil showing chemotropism in an angiospermic plant


Solution D.6








Cell division


Fruit ripening


Stem elongation

Abscisic acid

Closure of stomata


Solution D.7

(a) The figure shows phototropism. The growth movement of plant parts in the direction of light is called phototropism.

(b) Geotropism is the growth movement of plant parts towards earth's gravity while phototropism is the growth movement of plant parts towards light.

(c) Touch is the stimulus responsible for thigmotropism. Cuscuta shows thigmotropism.

(d) Gravity gives a positive response for the roots but a negative response for the shoot.

(e) Leaf tendril of sweet pea plant: