NCERT Class 10: Science-Exercise Solutions

Chapter 07-Control and Coordination-Exercise Solutions

NCERT Book Page Number-126

Q.1. Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin
Ans. (d) Cytokinin
Q.2. The gap between two neurons is called a :
(a) dendrite
(b) synapse
(c) axon
(d) impulse
Ans. (b) Synapse.
Q.3. The brain is responsible for :
(a) thinking
(b) regulating the heart beat
(c) balancing the body
(d) all of the above
Ans. (d) all of the above
Q.4. What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
Ans. Receptors are sensory structures (organs/tissues or cells) present all over the body. The receptors are either grouped in case of eye or ear, or scattered in case of skin.
Functions of receptors :
(i) They sense the external stimuli such as heat or pain.
(ii) They trigger an impulse in the sensory neuron which sends message to the spinal cord.
When the receptors are damaged, the external stimuli transferring signals to the brain are not felt. For example, in the case of damaged receptors, if we accidentally touch any hot object, then our hands might get burnt as damaged receptors cannot perceive the external stimuli of heat and pain.
Q.5. Draw the structure of a neuron and explain its function.
Ans. Neurons are the functional units of the nervous system. The three main parts of a neuron are axon, dendrites, and cell body.

Functions of the three parts of a neuron :
Axon : It conducts messages away from the cell body.
Dendrite : It receives information from axon of another cell and conducts the messages towards the cell body.
Cell body : It contains nucleus, mitochondria, and other organelles. It is mainly concerned with the maintenance and growth.
Q.6. How does phototropism occur in plants?
Ans. Plants show tropism in response to sunlight. This occurs in two different ways. When the shoot responds by bending towards the light, it is called positive phototropism. But when the root responds by bending away from the light it is called negative phototropism.
Q.7. Which signals will get disrupted in case of a spinal cord injury?
Ans. (i) The reflex arc connections between the input and output nerves meet in a bundle in the spinal cord. In fact, nerves from all over the body meet in a bundle in the spinal cord on their way to the brain. In case of any injury to the spinal cord, the signals coming from the nerves as well as the signals coming to the receptors will be disrupted.
(ii) Messages from various body parts will not be communicated to brain.
(iii) Messages from brain to body parts will not be communicated.
Q.8. How does chemical coordination occur in plants?
Ans. In animals, control and coordination occur with the help of nervous system. However, plants do not have a nervous system and thus plants respond to stimuli by showing movements. The growth, development and responses to the environment in plants is controlled and coordinated by a special class of chemical substances known as phytohormones. These are hormones produced in one part of the plant body and are translocated to other needy parts. For example, a hormone produced in roots is translocated to other parts when required. The five major types of phytohormone are auxins, gibberellins, cytokinins, abscisic acid, and ethylene. These phytohormones are either growth promoters (such as auxins, gibberellins, cytokinins, and ethylene) or growth inhibitors such as abscisic acid.
Q.9. What is the need for a system of control and coordination in an organism?
Ans. The maintenance of the body functions in response to changes in the body by working together of various integrated body systems is known as co-ordination. All the movements that occur in response to stimuli are carefully coordinated and controlled. In animals, the control and coordination movements are provided by nervous and muscular systems. The nervous system sends messages to and away from the brain. The spinal cord plays an important role in the relay of messages. In the absence of this system of control and coordination, our body will not be able to function properly. For example, when we accidentally touch a hot utensil, we immediately withdraw our hand. In the absence of nerve transmission, we will not withdraw our hand and may get burnt.
Q.10. How are involuntary actions and reflex actions different from each other?
Ans. Involuntary actions cannot be consciously controlled. For example, we cannot consciously control the movement of food in the alimentary canal. These actions are however directly under the control of the brain. On the other hand, the reflex actions such as closing of eyes immediately when bright light is focused show sudden response and do not involve any thinking. This means that unlike involuntary actions, the reflex actions are not under the control of brain.
Q.11. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.

Q.12. What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?