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.
Correct answer
Explanation
The correct answer is D, is composed of proteins and cells. The cornea is a clear layer made of cells and proteins, chiefly collagen fibres laid out in a regular pattern that keeps it transparent.
The cornea is the transparent, dome-shaped front part of the eye that covers the iris and the pupil. Light enters the eye through it, and it does most of the bending of light, more than the lens behind it. It has no blood vessels; it gets oxygen from the air and nutrients from tears and the aqueous humour. Because it has no blood supply, a donated cornea is rarely rejected, which makes corneal transplant one of the most successful kinds of transplant.
A is wrong because the light-sensitive screen of the eye is the retina, with its rods and cones. B is wrong because the muscular diaphragm that controls the size of the pupil is the iris. C is wrong because the cornea has no blood vessels at all.
Exam tip: cornea bends most light and has no blood vessels; iris controls the pupil; retina is the screen; eye donation means cornea donation.
Practice Questions
View allWhich one of the following statements about sound is NOT correct?
- A.Sound travels at a speed slower than the speed of light
- B.Sound waves are transverse waves
- C.Sound waves are longitudinal waves
- D.Sound travels faster in moist air than in dry air
Show answer
This statement is false, because sound in air travels as longitudinal waves, not transverse waves. In a longitudinal wave, the particles of the medium vibrate back and forth along the direction in which the wave moves, forming compressions and rarefactions.
Read the full explanation →Power of a lens of focal length 25 cm is
- A.+2.5 Dioptre
- B.+3 Dioptre
- C.+4 Dioptre
- D.+5 Dioptre
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Power is the reciprocal of the focal length in metres, so P = 1 ÷ 0.25 m = +4 D. The power of a lens tells how strongly it converges or diverges light.
Read the full explanation →In which one of the following devices, the light energy is converted into the electrical energy?
- A.Light-emitting diode
- B.Laser diode
- C.Solar cell
- D.Transistor
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A solar cell turns the energy of sunlight directly into electricity through the photovoltaic effect. A solar cell is a large p-n junction, usually made of silicon.
Read the full explanation →Two conducting wires of the same material and of equal lengths and equal diameters are first connected in parallel and then in series in a circuit across the same potential difference. The ratio of heat produced in parallel and series combinations is
- A.2:1
- B.4:1
- C.1:2
- D.1:4
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With the same voltage, heat varies inversely as resistance, and the parallel resistance is one-fourth of the series resistance. The two wires are identical, so each has the same resistance R. In series the total resistance is R + R = 2R; in parallel it is R/2.
Read the full explanation →The amount of air breathed in and out during a normal respiration by human lungs is referred to as
- A.Vital capacity
- B.Tidal volume
- C.Inspiratory volume
- D.Total lung capacity
Show answer
Tidal volume is the volume of air breathed in or out in one normal, quiet breath, about 500 mL in a healthy adult.
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