Topic: Sensory Organs
Subtopic: Eye and Vision
UV-B radiation: Ultraviolet radiation with wavelengths between 280-315 nm, can damage biological tissues.
Cornea: Transparent front layer of the eye covering the iris and pupil.
Inflammation: Response of tissues to injury or irritants, often causing redness, swelling, or pain.
Snow-blindness: Painful eye condition caused by overexposure of the cornea to UV-B rays.
Photokeratitis: Medical term for UV-induced corneal inflammation.
UV exposure: Contact of ultraviolet radiation with skin or eyes, potentially harmful.
Blindness: Loss or impairment of vision.
Ocular damage: Injury to structures of the eye, including cornea, lens, and retina.
Retina: Light-sensitive layer at the back of the eye transmitting images to the brain.
Protective measures: Sunglasses or UV-blocking goggles to prevent UV-related eye damage.
Phototoxicity: Damage caused to biological tissue due to light exposure.
Lead Question - 2022 (Abroad)
High dose of UV-B causes inflammation of cornea and is called as:
UV-blindness
Colour-blindness
Evening-blindness
Snow-blindness
Explanation: Excessive UV-B exposure damages the corneal epithelial cells, causing inflammation, pain, and temporary vision loss. This condition, commonly occurring in snow-covered areas or high altitudes, is known as snow-blindness or photokeratitis. Other options like color-blindness or evening-blindness involve retina or visual pigment defects, not UV-induced corneal inflammation. Answer: Snow-blindness. Answer: 4
Q1: Which part of the eye is primarily affected by UV-B rays?
Retina
Cornea
Lens
Optic nerve
Explanation: UV-B rays predominantly affect the cornea, causing epithelial cell damage, inflammation, and temporary vision impairment. Retina and lens may be affected by chronic UV exposure, but acute photokeratitis primarily involves the cornea. Correct answer: Cornea. Answer: 2
Q2: Photokeratitis is commonly caused by:
Visible light
UV-B radiation
Infrared radiation
X-rays
Explanation: Photokeratitis is inflammation of the cornea induced by UV-B radiation. Visible light does not cause corneal cell death. Infrared and X-rays affect deeper tissues or have different biological effects. Acute overexposure to UV-B leads to snow-blindness. Answer: UV-B radiation. Answer: 2
Q3: Which symptom is commonly associated with snow-blindness?
Headache only
Redness and pain in eyes
Nausea
Hearing loss
Explanation: Snow-blindness or photokeratitis presents with corneal inflammation, redness, tearing, pain, and temporary vision loss. Headache or nausea may occur secondarily, but primary symptoms involve eye discomfort due to UV-B-induced corneal epithelial damage. Answer: Redness and pain in eyes. Answer: 2
Q4: Protective measure against UV-B-induced corneal damage is:
Wearing sunglasses with UV filter
Consuming vitamin C
Sleeping in dark room
Eye drops only
Explanation: Sunglasses with UV filters block harmful UV-B radiation from reaching the cornea, preventing photokeratitis. Dietary vitamin C or eye drops do not provide immediate protection against UV exposure. Answer: Wearing sunglasses with UV filter. Answer: 1
Q5: Which occupation is at higher risk of snow-blindness?
Office workers
Mountaineers
Factory workers
Teachers
Explanation: Mountaineers and skiers face high UV-B exposure due to altitude and snow reflection, increasing risk of corneal inflammation or snow-blindness. Office workers and teachers have minimal UV exposure. Correct answer: Mountaineers. Answer: 2
Q6: Snow-blindness is a form of:
Retinal degeneration
Corneal inflammation
Optic neuropathy
Lens cataract
Explanation: Snow-blindness is acute corneal inflammation caused by UV-B exposure. It affects the corneal epithelium, not the retina, optic nerve, or lens. Symptoms resolve within days with protective measures and rest. Answer: Corneal inflammation. Answer: 2
Q7: Assertion (A): Snow-blindness is temporary.
Reason (R): Corneal epithelium regenerates within 24-48 hours.
(A) is correct but R is not correct
(A) is not correct but R is correct
Both A and R are correct and R explains A
Both A and R are correct but R does not explain A
Explanation: Snow-blindness symptoms are temporary because UV-B damages only the corneal epithelium, which regenerates rapidly within 24-48 hours. Both assertion and reason are correct, and the reason explains why vision impairment resolves without permanent damage. Answer: Both A and R are correct and R explains A. Answer: 3
Q8: Match the eye condition with its cause:
A. Snow-blindness 1. UV-B radiation
B. Cataract 2. Lens protein damage
C. Retinal degeneration 3. Aging or genetic factors
D. Colour-blindness 4. Cone photoreceptor defect
A-1, B-2, C-3, D-4
A-2, B-1, C-3, D-4
A-1, B-3, C-2, D-4
A-4, B-2, C-1, D-3
Explanation: Snow-blindness is caused by UV-B, cataracts by lens protein damage, retinal degeneration due to aging or genetics, and colour-blindness by cone photoreceptor defects. Matching correctly links conditions to their causes. Answer: A-1, B-2, C-3, D-4. Answer: 1
Q9: Inflammation of the cornea due to UV-B exposure is called ______.
Cataract
Photokeratitis
Glaucoma
Macular degeneration
Explanation: Photokeratitis, also called snow-blindness, is corneal inflammation caused by excessive UV-B exposure. Symptoms include redness, pain, and temporary vision loss. Cataracts and glaucoma involve different eye structures and mechanisms. Answer: Photokeratitis. Answer: 2
Q10: Which of the following statements about snow-blindness are correct?
Caused by UV-B exposure
Affects cornea
Temporary and self-limiting
Results from cone photoreceptor defect
Explanation: Snow-blindness results from UV-B exposure, affecting the cornea and is temporary due to epithelial regeneration. It is not caused by cone photoreceptor defects, which relate to colour-blindness. Correct statements are 1, 2, and 3. Answer: 1, 2, 3
Subtopic: Human Eye and Vision
Keyword Definitions:
Rods and Cones: Specialized photoreceptor cells in the retina responsible for vision in dim light (rods) and color vision (cones).
Blind Spot: Area on retina lacking photoreceptor cells where optic nerve exits the eye.
Fovea: Central pit in the retina densely packed with cones for sharp vision.
Iris: Coloured part of the eye controlling pupil size and light entry.
Lead Question - 2020 (COVID Reexam)
Match the following columns and select the correct option :
Column - I Column - II
(a) Rods and cones (i) Absence of Cones photoreceptor cells
(b) Blind Spot (ii) Cones are densely packed
(c) Fovea (iii) Photoreceptor cells
(d) Iris (iv) Visible coloured portion of the eye
1. (a)-(iii), (b)-(i), (c)-(ii), (d)-(iv)
2. (a)-(ii), (b)-(iii), (c)-(i), (d)-(iv)
3. (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)
4. (a)-(ii), (b)-(iv), (c)-(iii), (d)-(i)
Explanation: The rods and cones are photoreceptor cells, the blind spot has no cones or rods, the fovea is the central pit where cones are densely packed, and the iris is the visible coloured part of the eye. Thus, the correct matching is (a)-(iii), (b)-(i), (c)-(ii), (d)-(iv). Answer: Option 1.
1. The photoreceptor cells of the human eye are:
1. Only rods
2. Only cones
3. Rods and cones
4. Bipolar cells
Explanation: The retina contains specialized photoreceptor cells: rods, responsible for night vision and sensitivity to dim light, and cones, responsible for color vision and visual acuity. Both rods and cones together enable clear and bright vision. Answer: Option 3.
2. The fovea centralis is the region of:
1. Maximum rods
2. Maximum cones
3. No cones
4. No photoreceptors
Explanation: The fovea centralis is a small central depression in the retina where only cones are present in large numbers. It provides maximum visual acuity and is responsible for sharp central vision in humans. Answer: Option 2.
3. The blind spot in the eye is due to:
1. No bipolar cells
2. No rods and cones
3. No ganglion cells
4. Dense cones
Explanation: The blind spot is formed where the optic nerve exits the retina. This region lacks photoreceptor cells such as rods and cones, making it insensitive to light. No image is formed at this spot. Answer: Option 2.
4. The iris regulates:
1. Formation of aqueous humour
2. Entry of light by controlling pupil size
3. Accommodation of lens
4. Transmission of nerve impulses
Explanation: The iris is the visible colored portion of the eye that surrounds the pupil. Its smooth muscles regulate the size of the pupil, thereby controlling the amount of light entering the eye. Answer: Option 2.
5. Assertion (A): The fovea is the point of greatest visual acuity.
Reason (R): The fovea contains only cones densely packed.
1. Both A and R true, R correct explanation
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true
Explanation: The fovea centralis is a depression in the retina having densely packed cones without rods. It is responsible for maximum sharpness of vision. Both assertion and reason are true, and reason correctly explains assertion. Answer: Option 1.
6. Match the following:
Column I Column II
(a) Retina (i) Transparent window of the eye
(b) Cornea (ii) Light sensitive layer
(c) Lens (iii) Focuses light on retina
(d) Pupil (iv) Regulates entry of light
1. (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
2. (a)-(iii), (b)-(ii), (c)-(iv), (d)-(i)
3. (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)
4. (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)
Explanation: Retina is the light-sensitive layer of the eye, cornea acts as a transparent window, lens focuses light on retina, and pupil regulates entry of light. Thus, correct answer is (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv). Answer: Option 1.
7. Fill in the blank:
The light-sensitive pigment present in rods is ______.
1. Photopsin
2. Rhodopsin
3. Retinene
4. Melanin
Explanation: Rod cells contain the pigment rhodopsin, also called visual purple, which is highly sensitive to dim light. Rhodopsin helps in scotopic (night) vision and is derived from opsin protein and retinal (derived from vitamin A). Answer: Option 2.
8. Choose the correct statements regarding human eye:
(a) Lens is biconvex and transparent
(b) Aqueous humour is present between lens and retina
(c) Cornea and lens both help in focusing light
(d) Retina contains rods and cones
1. a, c and d only
2. a and b only
3. b and c only
4. a, b, c and d
Explanation: The human eye lens is biconvex and transparent. The aqueous humour lies between cornea and lens, not retina. Both cornea and lens help in focusing light. Retina contains rods and cones for vision. Thus, correct statements are a, c and d. Answer: Option 1.
9. The structure responsible for accommodation in the human eye is:
1. Cornea
2. Retina
3. Ciliary muscles
4. Iris
Explanation: The ciliary muscles alter the shape of the lens for near or distant vision. This ability of the eye to focus on near and far objects by changing lens curvature is called accommodation. Answer: Option 3.
10. Which vitamin deficiency causes night blindness?
1. Vitamin A
2. Vitamin D
3. Vitamin E
4. Vitamin C
Explanation: Night blindness is caused by vitamin A deficiency. Vitamin A is essential for the synthesis of retinal, a component of rhodopsin in rods. Its deficiency leads to impaired vision in dim light. Answer: Option 1.
Keyword Definitions:
Snow-blindness – Painful eye condition caused by excessive exposure to UV light, leading to temporary vision loss.
Antarctic region – High latitude region with strong sunlight reflection from ice and snow.
UV-B radiation – Part of ultraviolet spectrum (280–315 nm) that can damage skin and eyes.
Cornea – Transparent front layer of the eye that focuses light.
Retina – Light-sensitive layer at the back of the eye converting light into nerve signals.
Infra-red rays – Electromagnetic waves (700 nm–1 mm) mostly causing thermal effects.
Photokeratitis – Inflammation of cornea caused by UV exposure; another term for snow-blindness.
High light reflection – Increased brightness due to reflective surfaces like snow, can enhance UV exposure.
Eye freezing – Hypothetical damage due to low temperature; not a cause of snow-blindness.
Vision loss – Temporary or permanent impairment of sight.
Corneal inflammation – Swelling or damage to cornea, leading to pain, photophobia, or blurred vision.
Lead Question - 2020
Snow-blindness in Antarctic region is due to:
(1) High reflection of light from snow
(2) Damage to retina caused by infra-red rays
(3) Freezing of fluids in the eye by low temperature
(4) Inflammation of cornea due to high dose of UV-B radiation
Explanation: Snow-blindness occurs due to intense UV-B radiation reflecting from snow, causing inflammation of the cornea (photokeratitis). It is not caused by infra-red rays, freezing, or mere reflection. Correct answer is (4) Inflammation of cornea due to high dose of UV-B radiation.
1. Single Correct Answer: Which part of the eye is primarily affected in snow-blindness?
(1) Lens
(2) Retina
(3) Cornea
(4) Optic nerve
Explanation: UV-B radiation causes photokeratitis, which inflames the cornea. Other structures like retina or lens are not primarily involved. Correct answer is (3) Cornea.
2. Single Correct Answer: The major cause of snow-blindness is:
(1) Infra-red radiation
(2) High dose UV-B
(3) Freezing temperatures
(4) Dust particles in air
Explanation: Snow-blindness is caused by excessive UV-B exposure reflecting from snow surfaces. Infra-red or freezing do not cause this condition. Correct answer is (2) High dose UV-B.
3. Single Correct Answer: Photokeratitis is another term for:
(1) Cataract
(2) Snow-blindness
(3) Glaucoma
(4) Myopia
Explanation: Photokeratitis is inflammation of the cornea caused by UV light and is synonymous with snow-blindness. Other options are unrelated eye disorders. Correct answer is (2) Snow-blindness.
4. Assertion-Reason:
Assertion (A): Snow-blindness is common in snowy regions.
Reason (R): Snow reflects UV-B radiation increasing corneal exposure.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true
Explanation: Snow-blindness occurs in high UV-B reflective regions like Antarctica. Snow reflects UV-B, enhancing corneal damage. Both assertion and reason are correct, and R explains A. Correct answer is (1).
5. Single Correct Answer: Symptoms of snow-blindness include:
(1) Eye pain and photophobia
(2) Hearing loss
(3) Nausea
(4) Skin rash
Explanation: Snow-blindness causes corneal inflammation, resulting in eye pain, redness, and photophobia. Other symptoms like hearing loss or rash are unrelated. Correct answer is (1) Eye pain and photophobia.
6. Single Correct Answer: Prevention of snow-blindness includes:
(1) Using UV-protective goggles
(2) Staying in dark rooms
(3) Applying ice packs to eyes
(4) Using earplugs
Explanation: UV-protective goggles block UV-B radiation reflected from snow, preventing corneal damage. Other methods do not prevent snow-blindness. Correct answer is (1) Using UV-protective goggles.
7. Matching Type: Match exposure type with effect:
a. UV-B – i. Snow-blindness
b. Infra-red – ii. Thermal effect
c. Low temperature – iii. Freezing of tissues
d. Visible light – iv. Vision without damage
Options:
(1) a-i, b-ii, c-iii, d-iv
(2) a-ii, b-i, c-iv, d-iii
(3) a-i, b-iii, c-ii, d-iv
(4) a-iv, b-iii, c-ii, d-i
Explanation: UV-B causes snow-blindness (a-i), infra-red leads to thermal effects (b-ii), low temperatures can freeze tissues (c-iii), visible light allows vision without damage (d-iv). Correct answer is (1).
8. Fill in the blank: Snow-blindness is also called ______.
(1) Cataract
(2) Photokeratitis
(3) Glaucoma
(4) Myopia
Explanation: Inflammation of the cornea due to UV-B exposure is called photokeratitis, also referred to as snow-blindness. Other options are unrelated eye conditions. Correct answer is (2) Photokeratitis.
9. Single Correct Answer: Which factor enhances UV-B exposure in Antarctic regions?
(1) Reflection from snow
(2) Low air pressure
(3) High winds
(4) Low humidity
Explanation: Snow-covered surfaces reflect UV-B radiation, increasing eye exposure and causing snow-blindness. Air pressure, wind, or humidity do not directly enhance UV-B effects. Correct answer is (1) Reflection from snow.
10. Choose the correct statements:
(a) UV-B radiation causes snow-blindness
(b) Infra-red rays cause corneal inflammation
(c) Photokeratitis affects cornea
(d) Snow reflection increases risk
(1) a, c, d
(2) a, b, c
(3) b, c, d
(4) a, b, d
Explanation: UV-B radiation (a) inflames the cornea (c), and snow reflection (d) increases risk of snow-blindness. Infra-red rays do not cause corneal inflammation. Correct answer is (1) a, c, d.
Subtopic: Eye Structure
Keyword Definitions:
• Cornea: Transparent, avascular front layer of the eye allowing light entry.
• Collagen: Structural protein forming the dense matrix of corneal tissue.
• Convex: Curved outward shape aiding in light refraction.
• Avascular: Lacking blood vessels, as in cornea.
• Protective covering: Tissue that shields internal structures from damage.
• Transparent: Allows light to pass through without scattering.
• Eye-ball: Spherical organ for vision.
Lead Question (2019):
Which of the following statements is correct :
(1) Cornea is an external transparent and protective proteinacious covering of the eye-ball.
(2) Cornea consists of dense connective tissue of elastin and can repair itself.
(3) Cornea is convex, transparent layer which is highly vascularised.
(4) Cornea consists of dense matrix of collagen and is the most sensitive portion of the eye.
Explanation: Correct answer is (4). The cornea is composed of a dense matrix of collagen fibers, providing transparency and strength. It is avascular but richly innervated, making it the most sensitive part of the eye. Its convex curvature aids in light refraction for vision.
1) Single Correct Answer MCQ:
Which layer of the eye is avascular but highly sensitive?
(1) Sclera
(2) Cornea
(3) Retina
(4) Choroid
Explanation: Correct answer is (2). The cornea lacks blood vessels (avascular) but contains many sensory nerve endings, making it extremely sensitive to touch, pain, and temperature changes.
2) Single Correct Answer MCQ:
The cornea’s main structural protein is:
(1) Elastin
(2) Collagen
(3) Keratin
(4) Myosin
Explanation: Correct answer is (2). Collagen forms a dense matrix in the cornea, providing transparency, strength, and rigidity. Its organized fiber arrangement is crucial for clear vision.
3) Single Correct Answer MCQ:
Which part of the eye helps in light refraction due to convex shape?
(1) Lens
(2) Cornea
(3) Retina
(4) Iris
Explanation: Correct answer is (2). The cornea’s convex curvature refracts incoming light, focusing it onto the retina. This optical property is essential for forming clear images.
4) Single Correct Answer MCQ:
Which layer of the eye is transparent and avascular?
(1) Lens
(2) Sclera
(3) Cornea
(4) Choroid
Explanation: Correct answer is (3). The cornea is transparent, allowing light to pass into the eye. Its avascularity prevents scattering of light, ensuring clear vision.
5) Single Correct Answer MCQ:
Corneal sensitivity is mainly due to:
(1) Blood vessels
(2) Collagen
(3) Nerve endings
(4) Pigments
Explanation: Correct answer is (3). The cornea has a high density of sensory nerve endings, making it highly sensitive to touch, temperature, and pain, which helps in protective reflexes like blinking.
6) Single Correct Answer MCQ:
Which statement about the cornea is correct?
(1) Highly vascularized
(2) Composed mainly of collagen
(3) Contains elastin fibers
(4) Covers only the iris
Explanation: Correct answer is (2). The cornea is primarily made of collagen fibers arranged in a precise manner, providing strength, transparency, and resistance to mechanical stress.
7) Assertion-Reason MCQ:
Assertion (A): Cornea is the most sensitive part of the eye.
Reason (R): It has numerous sensory nerve endings but no blood vessels.
Options:
(1) A true, R true, R correct explanation
(2) A true, R true, R not correct explanation
(3) A true, R false
(4) A false, R true
Explanation: Correct answer is (1). The cornea’s extreme sensitivity is due to dense sensory innervation. Its avascularity ensures transparency without light scattering, making the reason correct and a valid explanation.
8) Matching Type MCQ:
Match the eye part with its property:
(a) Cornea - (i) Vascular
(b) Lens - (ii) Transparent
(c) Sclera - (iii) White, protective
(d) Retina - (iv) Photosensitive
Options:
(1) a-ii, b-ii, c-iii, d-iv
(2) a-i, b-ii, c-iii, d-iv
(3) a-ii, b-i, c-iii, d-iv
(4) a-ii, b-ii, c-i, d-iv
Explanation: Correct answer is (1). Cornea and lens are transparent, sclera is protective and white, retina is photosensitive. This classification matches their anatomical and functional properties.
9) Fill in the Blanks MCQ:
The cornea is composed of dense ______ and is the most sensitive portion of the eye.
(1) Collagen
(2) Elastin
(3) Keratin
(4) Myosin
Explanation: Correct answer is (1). Collagen fibers form the dense, transparent matrix of the cornea, making it strong and the most sensitive part of the eye due to innervation.
10) Choose the correct statements MCQ:
(1) Cornea is convex
(2) Cornea is avascular
(3) Cornea contains collagen fibers
(4) Cornea is the most sensitive eye portion
Explanation: Correct answer is (1,2,3,4). All statements are correct. The cornea is convex for refraction, avascular to maintain transparency, composed of collagen fibers, and highly sensitive due to rich nerve supply.
Chapter: Neural Control and Coordination
Topic: Human Eye and Vision
Subtopic: Lens and Accessory Structures
Keyword Definitions:
• Lens: Transparent, biconvex structure focusing light on retina.
• Ciliary body: Muscular structure controlling lens curvature and accommodation.
• Suspensory ligaments: Fibers holding the lens in position, attached to ciliary body.
• Retina: Light-sensitive inner layer with photoreceptors.
• Iris: Pigmented part of eye regulating pupil size.
• Cornea: Transparent front layer refracting light.
• Aqueous humor: Fluid maintaining intraocular pressure and nutrition.
Lead Question - 2018
The transparent lens in the human eye is held in its place by :
(A) smooth muscles attached to the ciliary body
(B) ligaments attached to the ciliary body
(C) smooth muscles attached to the iris
(D) ligaments attached to the iris
Explanation: The human eye lens is held by suspensory ligaments attached to the ciliary body. These ligaments adjust lens curvature during accommodation. Iris controls pupil size, not lens positioning. Hence, the correct answer is (B) ligaments attached to the ciliary body, which ensures stable focusing for near and distant vision.
1) Which part of the eye regulates the amount of light entering the eye?
(A) Lens
(B) Iris
(C) Retina
(D) Cornea
Explanation: Iris is the pigmented structure with muscles that regulate pupil size, thereby controlling the amount of light entering the eye. Lens focuses light, retina detects light, and cornea refracts incoming light. Hence, the correct answer is (B) Iris, which functions like a diaphragm of a camera.
2) Which region of retina has maximum visual acuity?
(A) Optic disc
(B) Fovea centralis
(C) Peripheral retina
(D) Blind spot
Explanation: The fovea centralis is a depression in the retina densely packed with cones, providing sharpest vision and maximum visual acuity. Optic disc is the blind spot, peripheral retina has rods for night vision, and blind spot has no photoreceptors. Correct answer is (B) Fovea centralis.
3) Clinical Question: A patient unable to see distant objects clearly is suffering from?
(A) Myopia
(B) Hypermetropia
(C) Presbyopia
(D) Astigmatism
Explanation: Myopia is near-sightedness, where distant objects appear blurred because image forms in front of retina. It is corrected using concave lenses. Hypermetropia affects near vision, presbyopia occurs due to aging lens, and astigmatism arises from irregular corneal curvature. Correct answer is (A) Myopia.
4) Which fluid fills the space between cornea and lens?
(A) Vitreous humor
(B) Aqueous humor
(C) Lymph
(D) Plasma
Explanation: The aqueous humor fills the anterior chamber between cornea and lens. It maintains intraocular pressure, nourishes lens and cornea. Vitreous humor fills posterior cavity, lymph and plasma are not eye fluids. Hence, the correct answer is (B) Aqueous humor. Clinical imbalance causes glaucoma.
5) The blind spot in human eye is due to:
(A) Absence of rods only
(B) Absence of cones only
(C) Absence of photoreceptors
(D) Absence of pigment
Explanation: The blind spot or optic disc lacks both rods and cones, making it insensitive to light. Thus, no image is formed in this region. Photoreceptors are present in all other retinal areas. Hence, the correct answer is (C) Absence of photoreceptors.
6) Assertion-Reason Type:
Assertion: Lens of human eye is flexible and can change its curvature.
Reason: Lens curvature changes due to contraction or relaxation of ciliary muscles.
(A) Both Assertion and Reason true, Reason explains Assertion
(B) Both Assertion and Reason true, Reason does not explain Assertion
(C) Assertion true, Reason false
(D) Both Assertion and Reason false
Explanation: The lens changes curvature for near and distant vision, a process called accommodation. This occurs because of ciliary muscle activity altering tension of suspensory ligaments. Thus, both statements are true, and Reason correctly explains Assertion. Correct answer is (A).
7) Matching Type:
Match eye structures with functions:
(A) Cornea - 1. Major refraction of light
(B) Retina - 2. Photoreception
(C) Iris - 3. Controls pupil size
(D) Lens - 4. Focuses light on retina
Options:
(A) A-1, B-2, C-3, D-4
(B) A-2, B-3, C-4, D-1
(C) A-3, B-1, C-2, D-4
(D) A-4, B-2, C-1, D-3
Explanation: Cornea performs major refraction, retina detects light, iris regulates pupil size, lens focuses light on retina. Hence, the correct answer is (A) A-1, B-2, C-3, D-4, covering essential functional anatomy of eye.
8) Fill in the Blanks:
The absence of _______ leads to color blindness in humans.
(A) Rods
(B) Cones
(C) Retina
(D) Iris
Explanation: Cones are responsible for color vision. Absence or defect in cones leads to color blindness, particularly red-green color blindness. Rods help in dim-light vision, retina contains both rods and cones, and iris regulates light entry. Thus, the correct answer is (B) Cones.
9) Clinical Question: A person gradually loses lens elasticity with age, facing difficulty in near vision. Condition is?
(A) Hypermetropia
(B) Presbyopia
(C) Myopia
(D) Glaucoma
Explanation: Presbyopia is an age-related condition where lens loses elasticity, making near vision difficult. It is corrected using bifocal lenses. Hypermetropia is congenital, myopia affects distance vision, glaucoma is due to raised intraocular pressure. Hence, the correct answer is (B) Presbyopia.
10) Choose the Correct Statements:
1. Rods are responsible for color vision.
2. Cones provide high visual acuity.
3. Lens is held by ligaments attached to iris.
4. Cornea provides major refractive power.
Options:
(A) 2 and 4 only
(B) 1 and 3 only
(C) 1, 2 and 3 only
(D) 2, 3 and 4 only
Explanation: Rods detect dim light, not color (false). Cones provide high visual acuity (true). Lens is held by ligaments attached to ciliary body, not iris (false). Cornea provides most refractive power (true). Thus, the correct answer is (A) 2 and 4 only.
Topic: Sensory Organs
Subtopic: Vision – Role of Vitamin A
Keyword Definitions:
• Carotene – A pigment found in vegetables, precursor of Vitamin A.
• Vitamin A – Fat-soluble vitamin essential for vision, immunity, and skin health.
• Retinal – Active form of Vitamin A involved in visual phototransduction.
• Photopigments – Light-sensitive molecules in retina, e.g., rhodopsin.
• Rod cells – Photoreceptor cells for dim light vision.
• Cone cells – Photoreceptor cells for color vision.
• Membrane discs – Structures in outer segment of photoreceptors containing photopigments.
• Visual cycle – Conversion of retinal between cis and trans forms during vision.
• Night blindness – Deficiency of Vitamin A affecting low-light vision.
• Beta-carotene – Plant-based precursor converted to retinal in body.
• Phototransduction – Conversion of light into electrical signals in retina.
Lead Question – 2017:
Good vision depends on adequate intake of carotene rich food. Select the best option from the following statements:
(a) Vitamin A derivatives are formed from carotene
(b) The photopigments are embedded in the membrane discs of the inner segment
(c) Retinal is a derivative of Vitamin A
(d) Retinal is a light absorbing part of all the visual photopigments
(A) b, c and d
(B) a and b
(C) a, c and d
(D) a and c
Explanation:
Correct option is C (a, c and d). Carotene from food is converted into Vitamin A derivatives like retinal, which acts as the light-absorbing component of photopigments in rods and cones. Photopigments are located in the outer segment, not inner segment. Adequate carotene intake ensures proper vision. (Answer: C)
1) Single Correct Answer MCQ:
Which vitamin deficiency causes night blindness?
(A) Vitamin C
(B) Vitamin A
(C) Vitamin D
(D) Vitamin E
Explanation:
Deficiency of Vitamin A impairs retinal formation, reducing rhodopsin levels in rod cells and leading to night blindness. Adequate intake of carotene-rich foods prevents this condition. (Answer: B)
2) Single Correct Answer MCQ:
The light-absorbing part of rhodopsin is:
(A) Opsin
(B) Retinal
(C) Beta-carotene
(D) Photopsin
Explanation:
Retinal is the chromophore that absorbs light in rhodopsin and other visual pigments. Opsin is the protein component that binds retinal. Beta-carotene is the dietary precursor of retinal. (Answer: B)
3) Single Correct Answer MCQ:
Beta-carotene is converted into which active compound in the retina?
(A) Vitamin C
(B) Retinal
(C) Rhodopsin
(D) Melanin
Explanation:
Dietary beta-carotene is enzymatically converted into retinal, a Vitamin A derivative, in the body. Retinal combines with opsin to form photopigments like rhodopsin, crucial for phototransduction and vision. (Answer: B)
4) Single Correct Answer MCQ:
Which photoreceptor is responsible for color vision?
(A) Rod
(B) Cone
(C) Bipolar cell
(D) Ganglion cell
Explanation:
Cones are photoreceptors responsible for color vision in bright light. Rods detect dim light but cannot distinguish colors. Cones contain photopsins that absorb specific wavelengths corresponding to red, green, or blue. (Answer: B)
5) Single Correct Answer MCQ:
Rhodopsin is present in which part of the photoreceptor?
(A) Inner segment
(B) Outer segment membrane discs
(C) Cell body
(D) Synaptic terminal
Explanation:
Rhodopsin is embedded in the membrane discs of the outer segment of rod cells. Light absorption by retinal in these discs initiates phototransduction. Inner segments contain organelles for metabolism. (Answer: B)
6) Single Correct Answer MCQ:
Which of the following is true regarding retinal?
(A) Derived from Vitamin C
(B) Light-absorbing molecule
(C) Found in lens
(D) Water-soluble vitamin
Explanation:
Retinal is the light-absorbing component of all visual photopigments, derived from Vitamin A. It is lipid-soluble and located in photoreceptor outer segments. It is essential for converting light into electrical signals. (Answer: B)
7) Assertion-Reason MCQ:
Assertion (A): Vitamin A deficiency can lead to night blindness.
Reason (R): Retinal is essential for photopigment formation in rods.
(A) Both A and R true, R explains A
(B) Both A and R true, R does not explain A
(C) A true, R false
(D) A false, R true
Explanation:
Both A and R are true. Night blindness occurs due to lack of retinal, which forms rhodopsin in rod cells. Without retinal, rods cannot detect dim light, causing vision problems. (Answer: A)
8) Matching Type MCQ:
Match:
1. Beta-carotene – (i) Precursor of retinal
2. Retinal – (ii) Light-absorbing chromophore
3. Rhodopsin – (iii) Rod photopigment
Options:
(A) 1-i, 2-ii, 3-iii
(B) 1-ii, 2-iii, 3-i
(C) 1-iii, 2-i, 3-ii
(D) 1-i, 2-iii, 3-ii
Explanation:
Correct matching: 1-i (Beta-carotene is retinal precursor), 2-ii (Retinal absorbs light), 3-iii (Rhodopsin is rod photopigment). These sequentially describe dietary intake to phototransduction process. (Answer: A)
9) Fill in the Blanks MCQ:
Photopigments are embedded in the _______ segment of photoreceptors.
(A) Inner
(B) Outer
(C) Cell body
(D) Axon terminal
Explanation:
Photopigments like rhodopsin are located in the outer segment of rods and cones. Light absorption here triggers electrical signals for vision. Inner segments house organelles for protein synthesis. (Answer: B)
10) Choose the correct statements MCQ:
1. Retinal is derived from Vitamin A.
2. Inner segment contains photopigments.
3. Vitamin A deficiency affects night vision.
4. Beta-carotene is converted into retinal.
Options:
(A) 1, 3, 4
(B) 1, 2, 4
(C) 2, 3, 4
(D) 1, 2, 3
Explanation:
Statements 1, 3, and 4 are correct. Retinal is Vitamin A derivative; deficiency leads to night blindness; beta-carotene is precursor. Photopigments are in outer, not inner, segments. (Answer: A)
Keyword Definitions
Photosensitive compound — Molecule in the eye responsible for detecting light and initiating vision.
Opsin — Protein component of visual pigments that binds retinal.
Retinal — Aldehyde form of vitamin A, a light-absorbing molecule in visual pigments.
Retinol — Alcohol form of vitamin A, not directly involved in light absorption.
Transducin — G-protein involved in phototransduction cascade but not the photosensitive pigment itself.
Retinene — Alternate name sometimes used for retinal.
Chapter: Human Physiology (NCERT Class 11) — Sub-topic: Sense Organs - Eye
Lead Question — 2016 (Phase 1)
Photosensitive compound in human eye is made up of:
(1) Guanosine and Retinol
(2) Opsin and Retinal
(3) Opsin and Retinol
(4) Transducin and Retinene
1. Guanosine and Retinol
2. Opsin and Retinal
3. Opsin and Retinol
4. Transducin and Retinene
Answer: 2. Opsin and Retinal
Explanation: The photosensitive pigment in the human eye is called rhodopsin, composed of the protein opsin and the aldehyde form of vitamin A, retinal. This pigment absorbs light and initiates the phototransduction cascade necessary for vision.
Guess Q1.
What is the main function of opsin in the visual pigment?
A. Absorbing light energy
B. Binding retinal and initiating phototransduction
C. Transporting electrons
D. Acting as a neurotransmitter
Answer: B. Binding retinal and initiating phototransduction
Explanation: Opsin is a protein that binds retinal to form rhodopsin. Upon light absorption, opsin undergoes a conformational change that triggers the phototransduction cascade converting light signals into neural signals.
Guess Q2.
Retinal is derived from which vitamin?
A. Vitamin C
B. Vitamin D
C. Vitamin A
D. Vitamin B12
Answer: C. Vitamin A
Explanation: Retinal is an aldehyde derivative of vitamin A, essential for vision. It binds to opsin to form the light-sensitive pigment rhodopsin in rod cells of the retina.
Guess Q3.
Which molecule directly absorbs photons of light in the eye?
A. Opsin
B. Retinal
C. Transducin
D. Retinol
Answer: B. Retinal
Explanation: Retinal is the chromophore that absorbs photons of light, triggering its isomerization from 11-cis to all-trans form, which initiates the visual signal transduction pathway.
Guess Q4.
Which of the following is NOT a component of the photosensitive pigment rhodopsin?
A. Opsin
B. Retinal
C. Retinol
D. Protein
Answer: C. Retinol
Explanation: Rhodopsin consists of opsin (protein) and retinal (aldehyde form of vitamin A). Retinol (alcohol form of vitamin A) is not part of the photosensitive pigment.
Guess Q5.
Transducin in the eye is:
A. A photosensitive pigment
B. A G-protein involved in phototransduction
C. A pigment molecule
D. A form of retinal
Answer: B. A G-protein involved in phototransduction
Explanation: Transducin is a G-protein activated by rhodopsin after light absorption. It transmits the signal downstream in the visual phototransduction pathway but is not itself photosensitive.
Guess Q6.
Which vitamin deficiency can lead to night blindness due to impaired formation of retinal?
A. Vitamin B12
B. Vitamin A
C. Vitamin C
D. Vitamin D
Answer: B. Vitamin A
Explanation: Vitamin A deficiency leads to insufficient retinal production, impairing rhodopsin formation and resulting in night blindness, as rods require rhodopsin for low-light vision.
Guess Q7. (Assertion-Reason)
Assertion (A): Rhodopsin is made of opsin and retinal.
Reason (R): Retinal absorbs light and changes conformation to initiate vision.
A. Both A and R are true, and R explains A
B. Both A and R are true, but R does not explain A
C. A is true, R is false
D. A is false, R is true
Answer: A. Both A and R are true, and R explains A
Explanation: Rhodopsin comprises opsin and retinal. Upon absorbing light, retinal undergoes isomerization, causing a conformational change in opsin that initiates the phototransduction cascade.
Guess Q8. (Matching)
Match the following components with their functions:
Column I
A. Opsin
B. Retinal
C. Transducin
D. Retinol
Column II
1. Protein part of rhodopsin
2. Light-absorbing chromophore
3. G-protein in phototransduction
4. Alcohol form of vitamin A
A. A-1, B-2, C-3, D-4
B. A-2, B-1, C-4, D-3
C. A-3, B-4, C-1, D-2
D. A-4, B-3, C-2, D-1
Answer: A. A-1, B-2, C-3, D-4
Explanation: Opsin is the protein in rhodopsin; retinal absorbs light; transducin is the G-protein transmitting the signal; retinol is the vitamin A alcohol form not involved in light detection.
Guess Q9. (Fill in the blanks)
The photosensitive pigment rhodopsin is composed of ________ and ________.
A. Opsin and Retinol
B. Opsin and Retinal
C. Transducin and Retinene
D. Guanosine and Retinol
Answer: B. Opsin and Retinal
Explanation: Rhodopsin is a visual pigment composed of the protein opsin and the light-absorbing molecule retinal, crucial for photoreception in the retina.
Guess Q10. (Passage-based)
Passage: "A pigment in the rod cells of the retina changes conformation upon absorbing light, triggering a cascade that converts light into electrical signals interpreted by the brain."
Which pigment is described here?
A. Melanin
B. Rhodopsin
C. Hemoglobin
D. Chlorophyll
Answer: B. Rhodopsin
Explanation: Rhodopsin, found in rod cells, is a photosensitive pigment composed of opsin and retinal. Upon light absorption, it undergoes conformational changes, initiating the visual signal transduction process.