NCERT Exemplar for Class 11 Biology Chapter-21 (Book Solutions)

Multiple Choice Questions (MCQs)

1. Chemicals which are released at the synaptic junction are called

(a) Hormones

(b) Neurotransmitters

(c) Cerebrospinal fluid

(d) Lymph

Ans: (b) Neurotransmitters

2. Potential difference across the resting membrane is negatively charged. This is due to differential distribution of the following ions

(a)  $\mathbf{N}{{\mathbf{a}}^{+}}$ and ${{\mathbf{K}}^{+}}$ ions

(b) $\mathbf{C}{{\mathbf{O}}^{3++}}$ and $\mathbf{C}{{\mathbf{l}}^{-}}$ ions

(c) $\mathbf{C}{{\mathbf{a}}^{++}}$ and $\mathbf{M}{{\mathbf{g}}^{++}}$ ions

(d) $\mathbf{C}{{\mathbf{a}}^{++}}$ and $\mathbf{C}{{\mathbf{l}}^{-}}$ ions

Ans: (a) $\text{N}{{\text{a}}^{\text{+}}}$ and ${{\text{K}}^{+}}$ ions

3. Resting membrane potential is maintained by

a. Hormones

b. Neurotransmitters

c. Ion pump

d. None of the above

Ans: (c) Ion pump

4. The function of our visceral organs is controlled by

a. Sympathetic and somatic neural system

b. Sympathetic and parasympathetic neural system

c. Central and somatic nervous system

d. None of the above

Ans: (b) Sympathetic and parasympathetic neural system

5. Which of the following is not involved in Knee-jerk reflex?

a. Muscle spindle

b. Motor neuron

c. Brain

d. Interneurons

Ans: (c) Brain

6. An area in the brain which is associated with strong emotions is

a. Cerebral cortex

b. Cerebellum

c. Limbic system

d. Medulla

Ans: (c) Limbic System

7. Mark the vitamin present in Rhodopsin

a. Vit A

b. Vit B

c. Vit C

d. Vit D

Ans: (a) Vit A

8. Human eyeball consists of three layers and it encloses

a. Lens, iris, optic nerve

b. Lens, aqueous humor and vitreous humor

c. Cornea, lens, iris

d. Cornea, lens, optic nerve

Ans: (b) Lens, aqueous humor and vitreous humor

9. Wax secreting gland present in the ear canal is called

a. Sweat gland

b. Prostate gland

c. Cowper’s gland

d. Ceruminous gland

Ans: (c) Cowper’s gland

10. The part of internal ear responsible for hearing is

a. Cochlea

b. Semicircular canal

c. Utriculus

d. Sacculus

Ans: (a) Cochlea

11. The organ of corti is a structure present in

a. External ear

b. Middle ear

c. Semicircular canal

d. Cochlea

Ans: (d) Cochlea

VERY SHORT ANSWER TYPE QUESTIONS

1. Rearrange the following in the correct order of involvement in electrical impulse movement-

Synaptic knob, dendrites, cell body, Axon terminal, Axon

Ans: Dendrites→ Cell body→ Axon→ Axon terminal→ Synaptic knob

2. Comment upon the role of the ear in maintaining the balance of the body and posture.

Ans: The vestibular apparatus is found in the inner ear. Semi-circular channels and an otolith make up this structure.

There are three planes to the semicircular canals.

The relative orientation of these canals sends messages to the brain and keeps the body balanced and in good posture.

3. Which cells of the retina enable us to see coloured objects around us?

Ans: Cone cells

4. Arrange the following in the order of reception and transmission of sound wave from the ear drum:

Cochlear nerve, external auditory canal, ear drum, stapes, incus, malleus, cochlea.

Ans: External auditory canal → eardrum → malleus → incus → stapes → cochlea  → Cochlear nerve

5. During resting potential, the axonal membrane is polarized, indicating the movement of +ve and –ve ions leading to polarization diagrammatically.

Ans: Neurons are excitable cells as their membranes are polarized. On the brain membrane, there are various types of ion channels. Different ions selectively permeate these ion channels. The axonal membrane is considerably more permeable to potassium ions (${{\text{K}}^{+}}$) and almost impermeable to sodium ions ($\text{N}{{\text{a}}^{+}}$) when a neuron is not conducting any impulses, i.e. when it is resting. Likewise, negatively charged proteins in the axoplasm are impermeable to the membrane. As a result, the axoplasm within the axon has a high concentration of ${{\text{K}}^{+}}$ and negatively charged proteins, but a low quantity of $\text{N}{{\text{a}}^{+}}$.

The fluid outside the axon, on the other hand, has a "low concentration of ${{\text{K}}^{+}}$ and a high concentration of $\text{N}{{\text{a}}^{+}}$, forming a concentration gradient." The active transport of ions by the sodium-potassium pump, that transfers $3\text{N}{{\text{a}}^{+}}$ outwards for $2{{\text{K}}^{+}}$ into the cell, maintains these ionic gradients throughout the resting membrane. As a consequence, the axonal membrane's outer side has a positive charge, whereas its inner surface has a negative charge and is thus polarized. The resting potential is the electrical potential differential across the resting plasma membrane.

6. Name the structures involved in the protection of the brain.

Ans: The skull provides excellent protection for the human brain. The brain is protected inside the skull by cranial meninges that are made up of three layers: an outside layer called dura mater, a very thin middle layer called arachnoid, and an interior layer called pia mater (that is in touch with the brain tissue). Piamater is a vascular membrane having a dense network of blood capillaries. Subdural space is the area between the dura mater and the arachnoid. Subarachnoid space is the area between the arachnoid and the pia mater. The cerebrospinal fluid (CSF) fills the subarachnoid space, acting as a shock absorber for the CNS.

7. Our reactions like aggressive behavior, use of abusive words, restlessness etc. are regulated by the brain, naming the parts involved.

Ans: Limbic system and hypothalamus.

8. What do grey and white matter in the brain represent?

Ans: The cerebral cortex is a layer of cells that covers the cerebral hemisphere and is folded into noticeable folds. Because of its greyish appearance, the cerebral cortex is known to as grey matter. The color comes from the concentration of neuron cell bodies in this area. The myelin sheath, that makes up the interior section of the cerebral hemisphere, protects the tract fibres. They provide the layer an impenetrable white appearance, hence the name "white matter."

9. Where is the hunger centre located in the human brain?

Ans: Hypothalamus

10. Which sensory organ is involved in vertigo (sensation of oneself or objects spinning around)?

Ans: Vestibular apparatus of inner ear

11. While traveling at a higher altitude, a person complains of dizziness and vomiting sensation. Which part of the inner ear is disturbed during the journey?

Ans: Vestibular apparatus (saccule, utricle and semicircular canals).

12. Complete the statement by choosing appropriate match among the following -

Ans: 

SHORT ANSWER TYPE QUESTIONS

1. The major parts of the human neural system are depicted below. Fill in the empty boxes with appropriate words.

Ans: 

CNS- Spinal cord

Human Neural System - Peripheral Neural System

PNS- Somatic neural system

Brain- Forebrain and Hindbrain

ANS- Parasympathetic NS

2. What is the difference between electrical transmission and chemical transmission?

Ans:

3. Neural systems and computers share certain common features. Comment in five lines. (Hint: CPU, input-output devices).

Ans: Neural systems and computers share certain common features. Below listed are some of the examples:

● The brain works similarly to a CPU (central processing unit).

● Olfactory and tactile receptors can be compared to keyboard and mouse.

● The sense organs act as input devices, similar to how a computer's keyboard, mouse, and scanner work.

● Ears could be compared to mike.

● Eyes could be compared to web cameras and scanners.

● Response to external stimuli is output; the way data is displayed on the computer \screen.

4. If someone receives a blow on the back of neck, what would be the effect on the person’s CNS?

Ans: If someone takes a hit to the back of the neck, the cervical vertebrae might get dislocated, causing harm to the spinal cord as it travels through the neural canal. A spinal cord injury can result in paralysis.

5. What is the function ascribed to the Eustachian tube?

Ans: The throat and the middle ear cavity are connected by the Eustachian tube. The Eustachian tube assists in the equalization of pressures on both sides of the eardrum.

6. Label the following parts in the given diagram using an arrow.

a. Aqueous chamber

b. Cornea

c. Lens

d. Retina

e. Vitreous chamber

f. Blind spot

Ans: 

LONG ANSWER TYPE QUESTIONS

1. Explain the process of the transport and release of a neurotransmitter with the help of a labeled diagram showing a complete neuron, axon terminal and synapse.

Ans: Synapses are connections that allow a nerve impulse to pass from one neuron to the next. The membranes of a presynaptic neuron and a postsynaptic neuron form a synapse that may or may not be divided by a synaptic cleft. A fluid-filled area called synaptic cleft separates the membranes of the pre- and postsynaptic neurons at a chemical synapse. The transmission of impulses at such synapses is aided by chemicals known as neurotransmitters. Vesicles containing these neurotransmitters are found in the axon terminals. 

When an impulse (action potential) reaches the axon terminal, it causes synaptic vesicles to migrate towards the plasma membrane, wherein they merge with the plasma membrane and release neurotransmitters into the synaptic cleft. The produced neurotransmitters get attached to receptors on the postsynaptic membrane that are particular to them. This interaction activates ion channels, enabling ions to enter the postsynaptic neuron and create a new potential. The newly created potential could be either excitatory or inhibitory.

2. Name the parts of the human forebrain indicating their respective functions.

Ans: The parts of the human forebrain are- cerebrum, thalamus and hypothalamus.

Below are the functions:-

• Cerebrum: The cerebrum, the largest region of the brain, controls temperature and initiates and directs movement. Speech, judgment, thinking and reasoning, problem-solving, emotions, and learning are all enabled by other parts of the cerebrum.

• Thalamus: The thalamus main job is to transmit motor and sensory information to the cerebral cortex. It also controls wakefulness, sleep, and alertness.

• Hypothalamus: The hypothalamus is a link between the neurological and endocrine systems, and its primary job is to keep the body in a state of homeostasis.

3. Explain the structure of the middle and internal ear with the help of a diagram.

Ans: 

Structure of Middle Ear- The middle ear is made up of the tympanic membrane and bony ossicles (tympanic cavity). The eustachian tube connects the middle ear to the pharynx, whereas the tympanic membrane divides the middle and external ears. The three bone ossicles are the malleus, incus, and stapes. The tympanic membrane is another name for the eardrum. It catches up sound waves and sends them to the bones' ossicles. The bony ossicles pick up the waves one by one and send them to the inner ear.

Structure of Inner Ear- The labyrinth is a fluid-filled chamber in the inner ear. The outer bony labyrinth and the interior membranous labyrinth are the two components of the labyrinth. The cochlea and semicircular canals are the two components of the labyrinth. Sound waves from the stapes are received by an oval window in the cochlea. The coiled section of the cochlea transmits auditory signals to the brain. The semicircular canals help the body retain its balance and posture.

The Class 11 Biology Chapter 21 - Neural Control and Coordination mainly consists of:

• The human neural system, consisting of the Central Nervous System (CNS) and the Peripheral Nervous System (PNS)

• The Neuron

The Central Nervous System (CNS) consists of the brain and spinal cord, along with the nerves connecting them.

The Peripheral Nervous System (PNS) consists of afferent and efferent nerve fibres. The afferent neurons send impulses from organs to the CNS, while the efferent neurons send impulses from CNS to organs. Thus, a complete, well-designed network is present within the human body.

Important Terminologies

• Neuron: The basic unit involved in transmission of impulses, to and from muscles and other parts to the brain.

• Axon: The long and slender fibral part of the nerve cell, which basically transmits the impulses away from the nerve cell.

• Dendrites: Short fibres that branch repeatedly and are assigned to transmit stimulations from other neural cells to the cell body.

• Soma: Cell body consisting of the nucleus and the DNA of the neurons.

• Node of Ranvier: A gap of the myelin sheath on the axons making the points uninsulated, which participate in exchange of ions to generate action potential. 

Free PDF download of NCERT Exemplar for Class 11 Biology Chapter 21 - Neural Control and Coordination solved by expert Biology teachers on Vedantu.com as per NCERT (CBSE) Book guidelines are available on the site.