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

A. Multiple Choice Type

(Select the most appropriate option in each case)

1. A plant hormone-related with the inhibition of senescence is

(a) Ethylene

(b) ABA

(c) Bromic acid

(d) GA

Ans: (d) GA

2. Apical dominance phenomenon is caused by

(a) Auxins

(b) GA

(c) Cytokinins

(d) ABA

Ans: (a) Auxins

3. Which of the following hormones regulate stomatal colour?

(a) Auxins

(b) GA

(c) ABA

(d) Cytokinins

Ans: (d) Cytokinins

4. Auxins are abundantly produced in

(a) base of the root

(b) base of the shoot

(c) shoot

(d) meristematic region of the shoot

Ans: (d) meristematic region of the shoot

5. A higher concentration of ethylene is found in

(a) green banana

(b) ripe banana

(c) fresh potato tuber

(d) green apple

Ans: (b) ripe banana

6. Common gibberellin is

(a) GA1

(b) GA2

(c) GA3

(d) GA7

Ans: (c) GA3

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

Ans: (c) negatively geotropic and positively phototropic

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

Ans: (c) either towards or away from the stimulus

B. Short Answer Type

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

Ans:

2. Differentiate between:

(a) Thigmotropism and geotropism

Ans: 

(b) Positive and negative tropism

Ans:

(c) Stimulus and response

Ans: 

(d) Phototropism and chemotropism

Ans: 

3. How is movement in plants different from that in animals?

Ans: Differences between movement in plants and movement in animals:

4. Name the stimulus which causes the following movements in plants.

phototropism, thigmotropism, hydrotropism and geotropism

Ans:

5. Name the following.

(a) Hormone that stimulates growth by cell division.

Ans: Cytokinin

(b) Growth retarding hormone in plants.

Ans: Abscisic acid

(c) Main auxin found in most plants.

Ans: Indole 3-acetic acid (IAA)

C. Descriptive Type

1. Define the following terms:

(a) Phytohormones

Ans: Phytohormones (also known as Plant hormones) are signal molecules obtained from plants and found in pretty low amounts in the environment. Plant hormones regulate every element of plant development and growth, from embryogenesis to organ size regulation, stress tolerance, pathogen defence, and reproductive development.

(b) Tropism

Ans: Tropism is a biological phenomenon in which a biological creature, usually a plant, grows or turns in reaction to environmental stimulation. This response is influenced by the stimulus's direction in tropisms. There are two kinds of tropism namely, positive and negative tropism.

(c) Clinostat

Ans: A clinostat is a device that uses rotation to counteract the effects of gravity on plant growth (gravitropism) and development (gravimorphism). Microgravity impacts on animal embryos, cell cultures, and spider webs have all been studied using it.

(d) Apical dominance

Ans: Apical dominance is a phenomenon in which the plant's main, central stem is dominant over (i.e., grows faster than) other side stems; on a branch, the main stem is even more dominant over its own side twigs.

(e) Parthenocarpy

Ans: Fruit formation without fertilisation is referred to as parthenocarpy. The technique results in a fruit that is infertile and devoid of seeds. This indicates that pollination results in the creation of totally seedless berries.

(f) Abscission

Ans: The regular separating of a plant component or organ is called abscission. It occurs when a plant part or organ is removed that is no longer required. Leaf abscission, for example, is the natural loss of an old leaf at the base of the petiole, which occurs in the autumn.

(g) Heliotropism

Ans: Heliotropism is a type of tropism that describes the diurnal or seasonal movement of plant components in response to the Sun's direction. The Ancient Greeks were aware of the tendency of some plants to migrate in the direction of the sun, a phenomenon known as tropism.

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

Ans: Below given is the List of five plant growth hormones with their important role:-

a. Auxins- 

● Encourage stem and root development and elongation.

● In the vascular cambium, promote cell division.

● The apical bud's auxins stop lateral buds from growing (apical dominance).

b. Gibberellins-

● Enhance the stem's longitudinal growth

● Have little effect on roots but induce stem elongation and leaf expansion.

● Break the buds' and tubers' dormancy.

● Encourage sugarcane internode lengthening.

● Delay in the onset of senescence

c. Abscisic acid-

● Dormancy is induced in buds, stems, and seeds.

● Flowering in short-day plants is inhibited.

● Many seeds are dormant because it induces and maintains dormancy.

● Cell division and cell elongation are both inhibited by this compound.

d. Cytokinins-

● Encourage the development of lateral buds.

● Stimulate cell division and delay the development of tissue senescence.

● Encourage the division of cells

● Leaves and other organs' senescence is postponed.

● Seeds that have been dormant for a long time must be awakened.

e. Ethylene-

● Causes apical dominance by inhibiting the formation of lateral buds.

● Buds and seeds are able to come out of their dormancy.

● Yellowing of leaves is involved with the ageing process of plant organs.

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

Ans: Tropic movement refers to a plant's movement in response to a stimulus in the environment; this movement is triggered by root and shoot growth. There are five primary types:

i. Phototropism is the movement of a plant in reaction to light; it causes the plant to grow in the direction of the light. It can be either positive (if facing the light) or negative (if facing away from the light).

ii. Chemotropism - The passage of pollen grains to the female gamete in seed plants is aided by the production of chemicals. This demonstrates chemotropism in a beneficial way.

iii. Geotropism is the movement of plants in reaction to gravity, which causes them to move in the same direction as gravity. Roots will expand downwards, exhibiting positive geotropism, whereas shoots will grow upwards, exhibiting negative geotropism.

iv. Thigmotropism is the reflex movement or action of a plant in response to being touched. The touch me not plant is a good example of this. The leaves droop as soon as they are touched.

v. Hydrotropism is the movement of plants in reaction to water; the roots of the plant will grow in the direction of the water.

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.

Ans: When seedlings are introduced in a pot filled with damp soil, the response of plants to gravity could be observed in the laboratory.

Plant roots have positive geotropism, that implies they grow in the direction of gravity, that is downward. This movement is beneficial to seedling growth. In order to find water and minerals, the roots must grow downwards in the soil.

Plant shoots exhibit negative geotropism, that means they grow in the opposite direction of gravity, upward. This movement is favourable to the plant's elongation. To allow the plant to expand in height, the shoots must grow upwards in the direction of the sun.

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

Ans: Tropism is a term used to describe when a plant responds to a stimulus by moving its growth. Tropism is a response to a stimulus that is particular to the direction of the stimulus. Plants can respond to stimuli in one of two ways: negatively or positively.

Positive tropic movements in plants tend to happen when the movement is towards the direction of stimuli.

Examples:

● Growth of shoots towards light

● Growth of roots towards water

Negative Tropic Movements in plants tend to happen when the movement is away from the stimuli.

Examples:

● Growth of roots away from light

● Growth of shoots away from water

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

Ans: 

● Aim: To prove that roots are more positively hydrotropic than geotropic.

● Required Materials: Wire netting or gauze, moist sawdust, wires, germinating bean seeds

● Procedure: 

i. Suspend a piece of wire netting or gauze from the ceiling with wires.

ii. Place 1 inch of damp sawdust on the wire netting.

iii. In the sawdust, plant some growing bean seeds.

● Observation: Under the effect of gravity, the radicles develop downwards through the wire netting as the seeds germinate. After a while, they begin to climb upwards towards the damp sawdust. The shoots continue to develop upwards.

● Inference: Gravity and water cause roots to grow in the same direction. The fact that roots grow towards the water and overcome gravity shows that they are more hydrotropic than geotropic. This suggests that water is a more powerful stimulant than gravity.

D. Structured/ Application/ Skill Type

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.

Ans: Apical dominance

(b) What plant hormone is responsible for the scientific phenomenon mentioned in (a).

Ans: Auxins

(c) Name one plant hormone which inhibits the said phenomenon.

Ans: Cytokinins

2.  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.

Ans: Ethylene

(b) Mention two characteristic features of this hormone.

Ans: Two characteristic features of Ethylene hormone:

● It is produced in senescent leaves and flowers, as well as in developing seeds and ripening fruits.

● Promotes and induces the ripening of fruits.

3. 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.

Ans: Chemotropism - Chemotropism is described as an organism's growth guided by chemical stimuli from outside the organism.

(b) Label the guidelines (1) to (4).

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

(c) Name two effective stimulants that help in the growth of part (2).

Ans: Sugars and peptones.

(d) Name two groups of plants where part (2) grows towards gametophyte with the help of the stimulants mentioned in (c).

Ans: Gymnosperms and angiosperms.

4. 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.

Ans: X: Stem tendrils, Y: Leaf tendrils. 

(b) Write the functions performed by the structures X and Y.

Ans: Function performed by X and Y structures:- The plant's stem and leaf tendrils let it climb up a structure.

(c) Name the phenomenon depicted and define it.

Ans: Thigmotropism. Thigmotropism is a mechanosensory response to a touch stimulation that causes directional growth movement. Thigmotropism is most commonly observed in twining plants and tendrils, but plant biologists have discovered it in blooming plants and fungi as well.

(d) How do the structures X and Y differ from each other?

Ans: Leaf tendrils (Y) emerge from the plant's leaf, whereas stem tendrils (X) emerge from the stem.

(e) Give examples of the plants which show the said phenomenon.

Ans: Sweet pea, Cuscuta and vines.

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

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