NCERT Solutions for Class 10 Science Chapter 4 - Control and Coordination

Question 1:

What happens at the synapse between two neurons?


Reflex action is a sudden, spontaneous and involuntary mechanical response to a stimulus by voluntary organs. Walking is movements of muscles of legs controlled by brain.

Question 2:

What happens at the synapse between two neurons?


Synapse is a junction between terminal arborization of one axon and dendrites of adjacent neuron. There is a gap between the two called synaptic cleft. As the electrical impulse reaches the terminal knobs, they release chemicals called neurotransmitter. These chemicals cross the gap and start a similar electrical impulse in the dendrite of next neuron.

Question 3:

Which part of brain maintains posture and equilibrium of body?



Question 4:

How do we detect the smell of an agarbatti (incense sticks)?


Sensory information regarding smell is received by olfactory lobes of brain. As the air passes through the nasal chambers, the olfactory epithelial cells get stimulated and convey the information as electrical impulses to brain which has the power of interpretation.

Question 5:

What is the role of brain in reflex action?


Thinking centres are located in brain. Brain is the co-ordinating centre. Brain and spinal cord in coordination with each other control all voluntary and involuntary actions.

Question 6:

What are plant hormones?


Plant hormones. These are chemical compounds secreted by plants which diffuse all around the other cells and regulate the activities. Plant hormones help to co-ordinate
(i) growth
(ii) development and
(iii) responses to the environment.

Question 7:

How is the movement of leaves of sensitive plant is different from movement of a shoot towards light?


Sensitive plant shows seismonastic movements. It is due to turgidity of cells. The movements of a shoot is a tropic movement.

Question 8:

Give an example of plant hormone that promotes growth.


(IAA) = Indole-3-Acetic Acid.

Question 9:

How do auxins promote growth of a tendril around a support?


Auxins synthesised in the tip helps the cells to grow longer. Some plants like the pea plant climb up other plants or support by means of tendrils. These tendrils are sensitive to touch. When they come in contact with any support, the part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. It is due to accumulation of auxins. This causes the tendril to circle around the object and thus cling to it.

Question 10:

Design an experiment to demonstrate hydrotropism.

  1. Take a porous pot and fill it with water.
  2. Keep a few freshly germinated pea seedlings in dried sand.
  3. As the water is not available in sand the root growing will bend towards porous pot filled with water.
  4. You will observe a hydrotropic curvature of the root as it grows towards water.
  5. This bending of root shows the movement as a response towards water.
Question 11:

How does chemical coordination take place in animals?


Chemical coordination is brought about by chemical messengers called hormones. They are secreted by endocrine glands (ductless glands). The hormones are carried by the blood to the site of action (target organs). The hormones are consumed during their action and provide wide ranging changes.

Question 12:

Why is the use of iodised salt advisable?


Iodine is necessary for the thyroid gland to make thyroxine hormone. Thyroxine regulates carbohydrate, protein and fat metabolism. It is required for growth. In case of deficiency of thyroxine, a disorder called goitre is caused.

Question 13:

How does our body respond when adrenaline is secreted into blood?


Adrenaline is secreted by adrenal gland during emergency. It prepares the body to respond effectively. The following are the actions of adrena line:

  1. Heart beats faster so as to pump the blood to muscles which need more energy.
  2. The blood supply to digestive system and skin is reduced due to contraction of muscles around these organs. This helps in diverting blood supply to muscles.
  3. Breathing becomes fast.
Question 14:

Why are some patients of diabetes treated by giving injections of insulin?


Insulin hormone is secreted by Islets of Langerhans of pancreas. This hormone helps in regulating sugar level in the blood. Its deficiency results in high sugar level and causes many harmful effects.

Question 15:

Which of the following is a plant hormone?

  1. Insulin
  2. Thyroxine
  3. Oestrogen
  4. Cytokinin


Question 16:

The gap between two neurons is called a:

  1. Dendrite
  2. Synapse
  3. Axon
  4. Impulse


Question 17:

The brain is responsible for:

  1. Thinking
  2. Regulating the heart beat
  3. Balancing
  4. All of the above

All of the above

Question 18:

What is the function of receptors in the body? Think of situations where receptors do not work properly. What problems are likely to arise?


Receptors. They are meant for receiving and detecting the information from environment. They are located in sense organs. They receive the information detected by tips of dendrites and convey as electrical impulses.

If receptors do not detect the information, there will not be any co-ordination. It may lead to accidents. Body response will not be there.

Question 19:

Draw a labelled diagram of neuron and explain its function.



  1. Nerve cells are specialised for conducting information via electrical impulses from one part of the body to another part.
  2. Dendrites acquire the information.
  3. Axon conducts information as electrical impulse.
  4. Terminal arborization pass the information as chemical stimulus at synapse for onward transmission.
Question 20:

How does phototropism occur in plants?


It is an established fact that plants bend towards light when they are exposed to it from one side of long axis. The aerial parts are positively phototropic and the roots and other underground parts bend away from light. These movements are due to interaction of light and auxins. The unilateral growth causes bending of stem as tip grows more rapidly.

Question 21:

Which signals will get disrupted in case of spinal cord injury?

  1. Spinal cord mainly controls reflex actions in the body. Spinal cord is made up of nerves which supply information to think about. Thus these actions will get disrupted in case of injury to spinal cord.
  2. Sensation and movement are restricted.
Question 22:

How does chemical coordination occur in plants?


Plants lack well organised control mechanism as in animals. However plants respond to light, touch and gravitational forces. Moreover growth and movements in plants are regulated by external and internal factors.

Plant growth regulators or phytohormones are the chemicals occurring in minute quantities and responsible for regulating metabolism, growth and development.

The important phytohormones are Auxins (Indole-3-acetic acid), Gibberellins, Cytokinins, Ethylene, and Abscisic acid (ABA). All growth processes are regulated by one or more phytohormones acting synergistically or antagonistically.

Question 23:

What is the need for a system of control and coordination in an organism?


Control and Coordination in the body is of two types i.e. nervous control and hormonal control. Nervous control is rapid. It takes place through electrical signals called nerve impulses. The hormonal control is through chemical messengers called hormones secreted by endocrine (ductless) glands and carried by blood to the target organs.

Question 24:

How are involuntary actions and reflex actions different from each other?


Reflex actions are the spontaneous responses by voluntary organs but involuntary actions are by the involuntary organs/muscles.

Question 25:

What is the difference between the manner in which movement take place in a sensitive plant and movement in our leg?


The movement in the leaves of a sensitive plant takes place due to sudden loss of water in the pulvini present at the base of all the leaves. The pulvini limp due to loss of water resulting in drooping and folding of leaves. The movement in our legs, on the other hand, takes place when ankles pull on the leg bones.