NCERT Solutions Exercise
Q1. Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin.
Answer: (d) Cytokinin.
Q2. The gap between two neurons is called a
(a) dendrite.
(b) synapse.
(c) axon.
(d) impulse.
Answer: (b) synapse.
Q3. The brain is responsible for
(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.
Answer: (d) all of the above.
Q4. What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
Answer: The receptor is located in the sensitive organs. They receive information from the environment. Through these, the person balances himself with the environment, if they do not work properly, then the brain will not be able to receive information or will delay, so the person will become insecure.
Q5. Draw the structure of a neuron and explain its function.
Answer: Nerve cell (neuron) is the functional and structural unit of the nervous system. It is divided into three parts.
(i) stem, (ii) cell, (iii) axon
Our body has sensory nerves and nerves. The sensory nerve carries the information to the spinal cord after receiving the stimulus from the receptor organs and the information from the carrier brain reaches the organs.
Q6. How does phototropism occur in plants?
Answer: Root responds by turning opposite to light and stem by turning in the direction of light, it is called phototropism. Oxygen hormone is secreted in the plant. It enters the dark part of the stem in the sunlight and the cells there are elongated and they are bent towards the light. This is called positive photoelectricity. Roots indicate negative.
Q7. Which signals will get disrupted in case of a spinal cord injury?
Answer: Reversible actions will not be able to complete. Apart from this, not all information will be transmitted properly.
Q8. How does chemical coordination occur in plants?
Answer: Plant cells secrete hormones. These hormones control growth, development and division. These hormones establish chemical coordination.
Q9. What is the need for a system of control and coordination in an organism?
Answer: If the system of control and coordination is not there in the organism, then the cells will not work as per the wishes of the organism. Therefore, it is very important to control them. It is effective for normal functions in multicellular organisms.
Q10. How are involuntary actions and reflex actions different from each other?
Answer: Involuntary Actions:
(i) These activities are controlled by the brain - beating of the heart, breathing.
(ii) It takes more linen to complete these activities.
Reversible Actions:
(i) These activities are controlled by the spinal cord. Usage : the withdrawal of the hand on touching a hot object.
(ii) These activities take very less time to complete.
Q11. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Answer: Nervous mechanism of action:
(i) Nervous system receives sensory information and sends its message and controls it.
(ii) The nervous system forms its own network in the body and has its own structural unit.
Reversible Actions:
(i) Hormones are secreted only by important glands in the organs of the body, these hormones control many activities for example - growth, development, reproduction etc.
(ii) Hormones themselves are secreted in the body.
Q12. What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
Answer: Movement in Mimosa Plants:
(i) The basis of motion in this plant is touch.
(ii) Here the motion is based on the bending and blooming of the husbands.
(iii) Here the size of the leaves also changes.
Speed of our leg:
(i) The basis of motion in this is the human nervous system.
(ii) Here the motion is based on the contraction and expansion of the muscles.
(iii) There is no change in the size of the foot or its muscles.
