NIOS Biology Coordination and Control – The Nervous and Endocrine Systems

NIOS Class 12 Biology Chapter 17 Solutions provide step-by-step answers to terminal exercises. This chapter deals with essential biology topics required for exam success. With simplified solutions, students can revise quickly and gain clarity on important points.

These solved exercises serve as a reliable resource for self-study and practice. By using them, learners can prepare more effectively and confidently, ensuring strong performance in the NIOS Class 12 Biology examination.

NIOS Class 12 Biology Chapter 17 Solutions

1. Name the two divisions of the nervous system.

(i) Central nervous system

(ii) Peripheral nervous system

2. What is gray matter?

Gray matter is the grayish cell bodies of the nerve cells located in the outer region (cerebral

cortex). 

3. Name the chemical involved in the transmission of a nerve impulse across a synapse.

Acetylcholine. 

4. Give two examples of sensory nerves.

• Cranial nerves from the eyes, ears, and nose.
• The facial nerve from the face.

5. Name the respective areas of the retina concerned with best vision and no vision.

The yellow spot lying at the visual axis is the place of best vision in the normal eye. Bling spot is the no vision area as it lacks sensory cells, thus no image is perceived.  

6. What is the role of the eustachian tube in the ear?

The Eustachian tube connects the tympanic cavity with the pharynx. It equalizes the pressure on both sides of the eardrum or tympanum.

7. Name the hormone and its source glands, whose deficiency leads to diabetes insipidus.

The hormone is Antidiuretic hormone (ADH) or vasopressin.  It is produced by the posterior lobe of the pituitary. 

8. What are pheromones?

Pheromones are the secretions given out by an individual into the environment, which bring about a specific response in other members of the same species.

• E.g..Common ants march on the floor or walls in a trail on an invisible path laid down by a secretion from their bodies.
• When disturbed, honey bees give out an alarm pheromone from their sting at the back and mandibles in the mouth. This alerts the inmates of the hive to face the attack.

9. Name and explain the event that happens immediately when a nerve fibre gets stimulated.

The event of stimulated nerve fiber is called depolarisation. The changes when a stimulus arrives at the nerve fibre are as follows:

• The axon membrane at that spot becomes more permeable to Na+ ions, which move inward and bring about depolarization or a localised change of charge from positive to negative (see diagram) on that spot.
• This point of depolarization itself becomes the stimulus for the adjoining area of the membrane, which in turn becomes depolarized.
• Meanwhile, the previous area becomes repolarized due to active movement of he sodium ions to the outside of the membrane by means of what is called ‘sodium pump’.
• And now the fibre is ready for the next wave of depolarization.

10. Are the endocrine glands and the ductless glands the same thing? Give one example.

Yes, the endocrine glands are also called ductless glands because their secretions are poured directly into the blood. Endocrine glands secrete hormones, which are carried by blood to the target organs. The stomach and duodenum also have similar secretions without any ducts. 

11. Describe one example of a conditioned reflex in humans.

Reflex action is an automatic, quick, and involuntary action in the body brought about by a stimulus. For example,

• You instantaneously withdraw your hand on accidentally touching a hot plate or a sharp thorn.
• Watering (salivation ) of the mouth takes place on seeing or just smelling a familiar tasty food.

12. List the functions of the medulla oblongata.

Medulla oblongata. This is the last part of the brain, which is connected to

the spinal cord. Its functions are as follows:

• (i) It is the center for breathing, coughing, swallowing, etc.
• (ii) It controls the heartbeat, the movement of the alimentary canal, and many other involuntary actions.

13. Differentiate between the sympathetic and parasympathetic nervous systems.

The sympathetic and parasympathetic nervous systems are part of the autonomic nervous system that controls the involuntary muscles and glands. 

The sympathetic nervous system prepares the body for facing emergencies, and the parasympathetic nervous system reestablishes the normal conditions once the emergency is over.

Sympathetic Nervous System	Parasympathetic Nervous System
Dilates the pupils	Constrict the pupils
Heartbeat speeds up	Slows down the heartbeat
A blood vessel on the skin constricts	Dilate the blood vessels on the skin
Dilates muscle blood vessels	Constricts muscle blood vessels
Dilates the bronchioles	Constricts the bronchioles
Relaxes the urinary bladder	Constricts the urinary bladder
Constricts sphincter	Relaxes sphincter
Increases sweating	Does not affect sweat secretion

14. What are the two principal tasks of insulin?

Insulin. It performs two principal tasks;

• Promotes glucose utilization by the body cells.
• Stimulates the deposition of extra glucose in the blood as glycogen in the liver.

15. Explain the following terms: (i) synapse, (ii) stimulus, and (iii) impulse

• (i) Synapse: Synapse is the point of communication between one nerve cell and another or between a nerve cell and a muscle.
• (ii) Stimulus: Stimulus is an agent or a sudden change of the external or the internal environment that results in a change in the activities of the organism.
• (iii) Impulse: An Impulse is a wave of electrical disturbance that travels across the nerve cell and its fibre.

16. Draw a diagram to show the arrangement of the bones inside the middle ear.

17. Write short notes on the following:

• (i) Myopia
• (ii) Taste buds
• (iii) Accommodation of the eye

(i) Myopia

Myopia, also known as near-sightedness, is the condition where nearby objects are clearly seen but not the distant ones because the image of the object is formed in front of the retina. This can be corrected by using a concave lens. 

(ii) Taste buds

Taste buds are located on the tongue to help perceive taste. For taste, there is direct contact of the substance with the sensory cells in the taste buds. 

(iii) Accommodation of the eye

Focusing the image on the retina is called accommodation of the eye. Changing the curvature of the elastic lens brings about accommodation.

• For distant vision: The lens is more flattened or thinner; this is the normal condition of the lens, which is kept stretched by the suspensory ligaments.
• For near vision, the circular ciliary muscles contract and tend to reduce the circumference of the eyeball there. This releases the tension on the suspensory ligament, and the lens becomes thicker (more rounded) on account of its own elasticity.

18. How do the sympathetic and parasympathetic nervous systems act differently on

(i) pupil of the eye, and (ii) urinary bladder?

(i) Pupil of the eye

The sympathetic system dilates the pupil while the parasympathetic nerve system constricts it. 

(ii) Urinary bladder

The sympathetic system relaxes the bladder muscles, and the parasympathetic system contracts the bladder muscles to cause the feeling of urination. 

19. Draw a labelled diagram of the cross-section of the spinal cord and the nervous pathway of a simple reflex concerned with it.

20. Explain the role of ciliary muscles in our eyes

The ciliary muscles, which are circular, contract and tend to reduce the circumference of the eyeball. This releases the tension on the suspensory ligament, and the lens becomes thicker (more rounded) on account of its own elasticity.

21. Taking the example of thyroxine secretion, explain what is meant by the feedback mechanism.

Hypothalamus releases a hormone, TSH-RH (TSH-Releasing Hormone), which instructs the anterior pituitary to release TSH (thyroid-stimulating hormone). The TSH stimulates the thyroid to release thyroxine. If the level of thyroxine in the blood increases, the pituitary stops the release of TSH. When the level of thyroxine falls in the blood, the thyroid gets stimulated to secrete more of it. In the feedback mechanism, the starting point of an activity receives back the information on whether to continue or increase, or to slow down or even stop.

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