Class Ten Science Chapter 7 NCERT Solutions

Chapter 7: Control and Coordination

Q.1. What is the difference between a reflex action and walking?

Ans. A reflex action is a rapid automatic response to a stimulus. It does not involve any thinking process. For example, we close our eyes immediately when the bright light is focused. Walking, on the other hand, is a voluntary action. It is under our conscious control.

Q.2. What happens at the synapse between two neurons?

Ans. A very small gap that occurs between the endings of the axon of one neuron and the dendrites of the other neuron is known as a synapse. It acts as a one-way valve to transmit impulses in one direction only. This unit-direction transfer of impulses occurs as the chemicals are produced in only one side of the neuron i.e., the axon’s side. From axon, the impulses travel across the synapse to the dendrites of the other neuron.

 Q.3. Which part of the brain maintains posture and equilibrium of the body?

Ans. Cerebellum, a part of the hindbrain is responsible for maintaining posture and equilibrium of the body.

Q.4. How do we detect the smell of an agarbatti (incense stick)?

Ans. The thinking part of our brain is the forebrain. It has separate areas that are specialised for hearing, smelling, sight, taste, touch, etc. The forebrain also has regions that collect information or impulses from the various receptors. When the smell of an incense stick reaches us, our forebrain detects it. Then, the forebrain interprets by putting it together with the information received from other receptors and also with the information already stored in the brain.

Q.5. What is the role of the brain in reflex action?

Ans. Reflex actions are sudden responses, which do not involve any thinking. For example, when we touch a hot object, we withdraw our hand immediately without thinking as thinking may take time which would be enough to get us burnt.

Reflex arcs are formed in the spinal cord and the information (input) reaches the brain. The brain is only aware of the signal and the response that has taken place. However, the brain has no role to play in the creation of the response.

Q.6. What are plant hormones?

Ans. Plant hormones or phytohormones are naturally occurring organic substances. These are synthesised in one part of the plant body (in minute quantities) and are translocated to other

parts when required. The five major types of phytohormones are auxins, gibberellins, cytokinins, abscisic acid and ethylene.

Q.7. How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?

Ans. The movement of leaves of the sensitive plant, Mimosa pudica or “touch me not”, occurs in response to touch or contact stimuli. This movement is independent of growth. The movement of a shoot towards light is known as phototropism. This type of movement is directional and growth dependent.

Q.8. Give an example of a plant hormone that promotes growth.

Ans. Auxin is an example of a growth-promoting plant hormone.

Q.9. How do auxins promote the growth of a tendril around a support?

Ans. Auxin is synthesised at the shoot tip. It helps the cell grow longer. When a tendril comes in contact with a support, auxin stimulates faster growth of the cells on the opposite side, so that the tendril forms a coil around the support. This makes the tendrils appear as a watch spring.

Q.10. Design an experiment to demonstrate hydrotropism. Ans. Take two small beakers and label them as A and B. Fill beaker A with water. Now make a cylindrical – shaped roll from a filter paper and keep it as a bridge between beaker A and beaker B, as shown in the figure. Attach few germinating seeds in the middle of the filter paper bridge. Now, cover the entire set – up with a transparent plastic container so that the moisture is retained.

Observation: The roots of the germinating seeds will grow towards beaker A.

This experiment demonstrates the phenomenon of hydrotropism.