Nervous System & Sense Organs – NDA Biology PYQs

NDA 2025-II

Q. 1. Identify the functions that are controlled by the hind brain of human being

(a) Involuntary actions such as blood pressure, salivation vomiting etc.

(b) Controlling the regions receiving sensory impulses from receptors

(c) Controlling the movement of voluntary muscles

(d) Sensation of hunger or being full

Answer: (a) Involuntary actions such as blood pressure, salivation vomiting etc.

Explanation: The hindbrain consists of the medulla oblongata, pons, and cerebellum. The medulla oblongata controls vital involuntary functions such as heart rate, blood pressure, breathing, salivation, and vomiting. These are automatic responses not under conscious control. The forebrain (cerebrum) controls voluntary muscle movement and higher functions. The hypothalamus controls hunger and satiety. The thalamus relays sensory impulses. Concept Tested: Medulla oblongata (hindbrain): controls involuntary actions such as blood pressure, salivation, and vomiting

★ JOVIK Exam Insight Brain division quick reference for NDA: Forebrain (cerebrum) – thinking, memory, voluntary movement. Hindbrain (medulla oblongata) – involuntary actions (heartbeat, breathing, salivation). Cerebellum (hindbrain) – balance and coordination. Hypothalamus – hunger, thirst, temperature.

 NDA 2024-I

Q. 2. The human eye is like a camera that has a lens with:

(a) fixed focal length and fixed aperture size.

(b) variable focal length and fixed aperture size.

(c) fixed focal length and variable aperture size.

(d) variable focal length and variable aperture size.

Answer: (d) variable focal length and variable aperture size.

Explanation: The human eye adjusts in two ways. The lens changes its curvature (and therefore focal length) through the action of ciliary muscles:  this process is called accommodation. The pupil (controlled by the iris) changes size to regulate the amount of light entering:  this is the variable aperture. A camera with a fixed lens has a fixed focal length and fixed aperture. The eye differs from a simple camera by having both variable focal length and variable aperture. Concept Tested: Human eye: variable focal length (accommodation by lens) and variable aperture (pupil size by iris)

 NDA 2021-II

Q. 3. Cornea in human eye

(a) is a light sensitive screen.

(b) is a muscular diaphragm.

(c) contains blood vessels.

(d) is composed of proteins and cells.

Answer: (d) is composed of proteins and cells.

Explanation: The cornea is the transparent, dome-shaped front surface of the eye. It is composed mainly of collagen proteins and specialised cells called keratocytes. The cornea is avascular:  it has no blood vessels (it receives oxygen directly from the air and nutrients from the aqueous humour). It is not light-sensitive (the retina is the light-sensitive screen). It is not muscular (the iris is the muscular diaphragm that controls pupil size). Concept Tested: Cornea: transparent, avascular, composed of collagen proteins and cells (keratocytes)

★ JOVIK Exam Insight In NDA, each eye structure has one job. Retina – light-sensitive screen. Iris – muscular diaphragm (controls pupil). Cornea – transparent outer covering (avascular, made of proteins). Lens – focuses light. A common trap is selecting ‘cornea’ when ‘retina’ is the answer, or vice versa.

 NDA 2018-II

Q. 4. Which one of the following depicts the correct circuit of a reflex arc?

(a) Effector – sensory neuron – spinal cord – motor neuron – receptor

(b) Receptor – sensory neuron – spinal cord – motor neuron – effector

(c) Receptor – sensory neuron – brain – motor neuron – effector

(d) Sensory neuron – receptor – brain – effector – motor neuron

Answer: (b) Receptor – sensory neuron – spinal cord – motor neuron – effector

Explanation: A reflex arc is the neural pathway for a reflex action. The correct sequence is: Receptor (detects stimulus) → Sensory neuron (carries impulse to spinal cord) → Spinal cord (integration/relay) → Motor neuron (carries impulse to effector) → Effector (muscle or gland that responds). Reflex arcs are processed in the spinal cord, not the brain, which allows a fast response without conscious thought. Concept Tested: Reflex arc: Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector

★ JOVIK Exam Insight The reflex arc sequence is a high-frequency NDA topic. The key point: reflex arcs go through the spinal cord, not the brain. This makes reflexes faster than voluntary responses. The sequence Receptor → Sensory → Spinal cord → Motor → Effector must be memorised in order.

 NDA 2018-I

Q. 5. Which one of the following elements is needed in the human body to transfer electrical signals by nerve cells?

(a) Lithium

(b) Sodium

(c) Rubidium

(d) Caesium

Answer: (b) Sodium

Explanation: Nerve impulse transmission (action potential) depends on the movement of sodium (Na⁺) and potassium (K⁺) ions across the nerve cell membrane. At rest, there is a higher concentration of Na⁺ outside and K⁺ inside the cell. When a nerve is stimulated, Na⁺ rushes into the cell –  this creates a wave of depolarisation (the action potential) that travels along the nerve fibre. Lithium, rubidium, and caesium are also alkali metals but are not the physiologically relevant ions for nerve signalling. Concept Tested: Sodium (Na⁺) ions are essential for generating action potentials and transmitting nerve impulses

 NDA 2017-I

Q. 6. Colour vision in human eyes is the function of photoreceptor cells named

(a) Rods

(b) Cones

(c) Blind spot

(d) Fovea

Answer: (b) Cones

Explanation: The retina contains two types of photoreceptor cells. Rods are sensitive to low light and detect light and dark (scotopic/dim-light vision). Cones are responsible for colour vision and function in bright light. There are three types of cones, each sensitive to red, green, or blue light. The blind spot is where the optic nerve exits:  it has no photoreceptors. The fovea is the area of sharpest vision, densely packed with cones but not a cell type itself. Concept Tested: Cones: photoreceptor cells responsible for colour vision; rods are for dim-light (black-and-white) vision

 NDA 2015-I

Q. 7. Which one of the following is not a part of nerves?

(a) Axons

(b) Connective tissues

(c) Schwann cells

(d) Smooth muscles

Answer: (d) Smooth muscles

Explanation: A peripheral nerve is composed of bundles of axons (nerve fibres), connective tissue layers (endoneurium, perineurium, and epineurium surrounding the nerve bundles), and Schwann cells (which form the myelin sheath around axons in peripheral nerves). Smooth muscles are involuntary muscles found in organs such as the stomach, intestine, and blood vessels:  they are not part of nerve structure. Concept Tested: Smooth muscles are not part of nerve structure; nerves contain axons, connective tissue, and Schwann cells

 NDA 2013-II

Q. 8. Presbyopia is a visual defect caused by

(a) Elongation of the eye ball.

(b) Shortened curvature of the eye lens.

(c) Weakening of the ciliary muscles.

(d) Gradually increasing flexibility of the eye lens.

Answer: (c) Weakening of the ciliary muscles.

Explanation: Presbyopia is an age-related condition in which the eye gradually loses the ability to focus on near objects. It is caused by two changes that occur with ageing: the lens loses elasticity and becomes less flexible, and the ciliary muscles weaken. Together, these reduce accommodation:  the ability to change lens curvature. Option (d) states ‘gradually increasing flexibility’ which is the opposite of what happens. The primary cause stated in option (c):  weakening of ciliary muscles:  is correct. Concept Tested: Presbyopia: age-related weakening of ciliary muscles (and reduced lens elasticity) causes loss of near-vision accommodation

 NDA 2013-I

Q. 9. The main thinking part of the brain is

(a) midbrain

(b) hypothalamus

(c) forebrain

(d) hindbrain

Answer: (c) forebrain

Explanation: The forebrain is the largest and most complex part of the human brain. It includes the cerebrum, which is responsible for all higher cognitive functions: thinking, reasoning, memory, learning, language, and voluntary movement. The forebrain is therefore the main thinking part. The hypothalamus (also part of the forebrain) controls basic drives. The midbrain relays signals. The hindbrain controls involuntary functions and balance. Concept Tested: Forebrain (cerebrum): the main thinking part of the brain; responsible for reasoning, memory, and voluntary control

 NDA 2010-I

Q. 10. Which part of brain controls fine movement, maintains balance and equilibrium of the body and muscle tone in a human being?

(a) Cerebrum

(b) Thalamus

(c) Cerebellum

(d) Hypothalamus

Answer: (c) Cerebellum

Explanation: The cerebellum is located at the back of the brain, below the cerebrum. It coordinates fine and precise movements, maintains posture, balance, and equilibrium, and regulates muscle tone. When the cerebellum is damaged, a person loses coordination and balance. The cerebrum handles voluntary movement and thinking. The thalamus relays sensory signals. The hypothalamus controls internal body conditions. Concept Tested: Cerebellum: controls fine movement, balance, equilibrium, and muscle tone

Q. 11. Among the following elements, which one is essential for the transmission of impulses in the nerve fibre?

(a) Calcium

(b) Iron

(c) Sodium

(d) Zinc

Answer: (c) Sodium

Explanation: The transmission of nerve impulses (action potentials) depends on the rapid influx of sodium (Na⁺) ions into the nerve cell. At rest, the membrane is polarised with Na⁺ concentrated outside. Stimulation opens sodium channels and Na⁺ rushes in:  this depolarisation propagates as the nerve impulse. Calcium plays a role in neurotransmitter release at synapses. Iron is part of haemoglobin. Zinc supports enzyme function. Sodium is the primary ion for impulse transmission. Concept Tested: Sodium (Na⁺) ion influx generates action potential; essential for nerve impulse transmission

★ JOVIK Exam Insight NDA has tested ‘sodium and nerve impulse’ in both NDA 2018-I (Q5) and NDA 2010-I (Q11). This is a repeated concept. The answer is always sodium. Other alkali metals (lithium, caesium, rubidium) and trace elements (calcium, iron, zinc) are distractors.

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