NCERT Class 10 Chapter 6 Control and Coordination CBSE Board Sample Problems Long Answer

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(a) What is (i) photoropism and (ii) geotropism? With labelled diagrams describe an activity to show that light and gravity change the direction that plant parts grow in.

(b) Mention the role of each of the following plant hormones: i) Auxin ii) Abscisic acid


(a) (i) Phototropism: The movement of a plant or its part in response to light is called phototropism.

(ii) Geotropism: The movement of a plant or its part in response to gravity is called geotropism.

Activity to show that light and gravity change the direction that plant part grows

i. Fill a conical flask with water.

ii. Cover the neck of the flask with a wire mesh.

¡ii. Keep two or three freshly germinated bean seeds on the wire mesh.

iv. Take a cardboard box which is open from one side.

v. Keep the flask in the box in such a manner that the open side of the box faces light coming from a window.

vi. After two or three days, you will notice that the shoots bend towards light and roots away from light.

Phototropism and Geotropism

Phototropism and Geotropism

(b) (i) Auxin: - It promotes growth and cell elongation. (ii) Abscisic acid: It inhibits growth and causes wilting of leaves.


(a) Draw the structure of a neuron and label the following on it: Nucleus, Dendrite, Cell body and Axon

(b) Name the part of neuron:

i) Where information is acquired.

ii) Through which information travels as an electrical impulse.


(i) Information is acquired through dendrite.

(ii) From the dendrite to the cell body and then along the axon to it’s end.

Acquired through dendrite

Acquired through Dendrite


What are the different stimuli to which plants are exposed and mention the way in which they respond to these stimuli?


Ans. Plants are exposed to several stimuli.

(i) One of the most common stimulus is the stimulus of sunlight. It is a well-known fact that the shoot system always bends towards light and the root system bends away from light. This is known as Phototropism.

Plants are exposed to several stimuli.

Plants Are Exposed to Several Stimuli

(ii) Plants are exposed to the stimulus of gravity. The shoot always grows away from earth and the root grows towards the earth’s gravitational pull. This response of shoot and root towards gravity of the earth is termed as Geotropism.

Plants are exposed to the stimulus of gravity

Plants Are Exposed to the Stimulus of Gravity

(iii) Similarly the shoot and the root system respond to the stimulus of water or moisture and this response is termed as Hydrotropism. The shoot system is negatively hydrotropic, while the root system is positively hydrotropic.

The shoot system is negatively hydrotropic

The Shoot System is Negatively Hydrotropic

(iv) The response of the plant part towards chemical is known as chemotropism.

Example- Growth of pollen tube towards ovules. These movements are called tropic movements and brought by chemical substances called plant hormones.

Growth of pollen tube towards ovules

Growth of Pollen Tube Towards Ovules

(v) Movement of a plant part in response to the stimuli touch is called Thigmotropism. Example Tendrils

Called Thigmotropism

Called Thigmotropism


What is Phototropism? How does phototropism occur in plants?


Phototropism occur in plants

Phototropism Occur in Plants

The directional movement of a plant? Plant part in response to light is called Phototropism. The shoot responds by bending towards light while roots respond by bending away from the light. We know that the plant stem responds to light and bend towards it due to the action of auxin hormone. This happens as follows

  • When sunlight falls on the plant, the auxin hormone present at the tip of the stem spreads uniformly down the stem. Due to the equal presence of auxin, both the sides of the stem grow straight and with same rapidity.

  • When the light falls on the right side of the stem, then the auxin hormone collects in the left side of the stem, away from the light because auxin hormone prefers to stay in shade i.e. move away from light. Thus, more auxin hormone is present in the left side of stem as compared to the right. The left side of stem, grows faster than its right side and therefore, the stem bends towards the right side (direction of light).

  • The effect of auxin on the growth of a root is exactly opposite to that on a stem. Auxin hormone increases the rate of growth in stem but it decreases the rate of growth in a root. The side of root away from light will have all the auxin concentrated in it. Due to this, the side of root which is away from light will grow slower than the other side and make the roots bends away from light.


Give differences between Tropic movement and nastic movement.


The difference is as follows:

Tropic Movement and Nastic Movement
Tropic movement and nastic movement

Tropic Movements

Nastic Movements

1. It can be observed in stems and roots.

1. It can be observed in leaves and petals of flowers.

2. It is due to unilateral stimulus which causes unequal growth on the two sides of a stem, root and tendril.

2. The movement occurs due to stimulus of light and temperature.

3. It is a growth movement.

3. It is not a growth movement.

4. It depends on the direction of stimulus applied like gravity, light, touch, water and chemical substances.

4. It does not depend on the direction of stimulus applied.


a. How is the movement in “touch me not plant” different from that of shoot towards light?

b. Describe positive and negative geotropism through an experiment



Touch Me Not Plant
Touch me not plant

Shoot towards light

Touch me not plant

i. Is a slow process

i. Is a fast process

ii. It’s directional

ii. Non-directional

iii. It’s growth related

iii. It’s not growth related

b. Set up: i. Take a potted plant and keep it in sunlight in a horizontal position.

ii. Observe the growth of shoot and root of the plant.

Observation: i. The roots bend downward showing positive geotropism

ii. The shoots bend upwards towards sunlight showing negative geotropism.


(i) Given below ¡s the diagram of human brain:

Human brain

Human Brain

Label the parts of the brain which:

(a)Help in walking in a straight line.

(b)Help in controlling blood pressure.

(c) Help in answering questions in the class.

(d) Gives a sensation of feeling full.

(ii) Why are diabetic patients treated by giving insulin injections?

(iii) Give reason: Multicellular organisms use chemical means of communication in addition to electrical communication


i. a. Cerebrum

b. Medulla

c. cerebrum

d. hypothalamus/forebrain

ii. As diabetic patients have high sugar levels and insulin lowers it.

iii. In electrical communication, information does not reach each and every cell and electrical impulse is not generated continuously by cells.

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