Which part of eye controls size of a pupil?
- A.Cornea
- B.Iris
- C.Retina
- D.Eye Lens
Correct answer
Explanation
The correct answer is B, the iris. The iris is the coloured ring in front of the lens, formed by the front part of the choroid, and the muscles in it widen or narrow the pupil so that the right amount of light reaches the retina; in dim light the pupil opens wide and in bright light it closes down. Option A is wrong because the cornea is the transparent front part of the sclera through which light enters, and most of the bending of light happens there, but it does not move. Option C is wrong because the retina is the innermost light sensitive layer that carries the rods and cones and converts light into nerve impulses. Option D is wrong because the eye lens is the biconvex crystalline structure that changes its curvature through the ciliary muscles to focus on near and far objects, a process called accommodation. The pupil itself is only the opening in the centre of the iris.
Read the full article: Sense Organs: Eye, Ear, Nose, Tongue and Skin
Practice Questions
View allWhich of the following parts of the human body contains gustatory receptors?
- A.Eyes
- B.Nose
- C.Tongue
- D.Skin
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Gustatory receptors are the receptors of taste, and they lie in the taste buds of the tongue, which sit mostly on small projections called papillae; they are stimulated by chemicals dissolved in saliva and send impulses to the brain.
Read the full explanation →Which is the smallest bone in the human body?
- A.Malleus
- B.Incus
- C.Stapes
- D.Nasal bone
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The stapes, also called the stirrup because of its shape, lies in the middle ear and is the smallest bone in the human body; it passes the vibration received from the eardrum on to the oval window of the inner ear.
Read the full explanation →Which part of the ear is responsible for maintaining the balance of the body?
- A.Cochlea
- B.Semicircular canals
- C.Tympanic membrane
- D.Eustachian tube
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The three semicircular canals of the inner ear are set at right angles to one another and are filled with fluid; movement of the head moves the fluid, which stimulates the receptors and tells the brain about the position and motion of the head, so that balance or equilibrium is…
Read the full explanation →The light sensitive layer of the human eye on which the image is formed is the:
- A.Cornea
- B.Choroid
- C.Sclera
- D.Retina
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The retina is the innermost coat of the eyeball and it carries the photoreceptor cells, the rods and the cones, which convert light into nerve impulses that the optic nerve carries to the brain; the image formed on the retina is real and inverted, and the brain interprets it as…
Read the full explanation →The rod cells of the retina contain which pigment?
- A.Melanin
- B.Rhodopsin
- C.Haemoglobin
- D.Chlorophyll
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Rhodopsin, also called visual purple, is the pigment of the rod cells; it is extremely sensitive to light, which is why rods allow us to see in dim light, though only in shades of black and white.
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