Human eye can see objects at different distances with contrasting illuminations. This is due to
- A.far-sightedness
- B.near-sightedness
- C.far-sightedness and near-sightedness
- D.accommodation of eye
Correct answer
Explanation
The correct answer is D, accommodation of eye. The eye adjusts the focal length of its lens to bring both near and far objects into focus on the retina, and this ability is called accommodation.
The eye lens is soft and flexible. The ciliary muscles around it relax to make the lens thinner when we look at distant objects, and contract to make it thicker when we look at something close. In a normal eye this lets us see clearly from about 25 cm, the near point, to infinity, the far point. The iris and pupil also adjust to light, opening wider in dim light and narrowing in bright light. With age the lens stiffens and accommodation weakens, a condition called presbyopia.
A, far-sightedness (hypermetropia), is a defect in which near objects look blurred.
B, near-sightedness (myopia), is a defect in which distant objects look blurred.
C, far-sightedness and near-sightedness together are defects of vision, not the reason a healthy eye sees well.
Exam tip: accommodation is done by the ciliary muscles; normal near point 25 cm, far point infinity.
Practice Questions
View allWhich of the following are nitrogen-fixing plants?
1. Alfalfa
2. Amaranth
3. Chickpea
4. Clover
5. Purslane (Kulfa)
6. Spinach
Select the correct answer using the code given below:
- A.1, 3 and 4 only
- B.1, 3, 5 and 6 only
- C.2, 4, 5 and 6 only
- D.1, 2, 4, 5 and 6
Show answer
Alfalfa, chickpea and clover are legumes, and legumes fix nitrogen. Plants of the legume family (Fabaceae) carry root nodules that house Rhizobium bacteria.
Read the full explanation →The mass number of an element is NOT changed when it emits
- A.Alpha and Beta radiations only
- B.Alpha and Gamma radiations only
- C.Beta and Gamma radiations only
- D.Alpha, Beta and Gamma radiations
Show answer
Neither beta nor gamma emission changes the total number of protons and neutrons in a nucleus, so the mass number stays the same.
Read the full explanation →Which one among the following statements about facilitated transport in plants is correct?
- A.All passive transports are types of facilitated transport.
- B.Facilitated transport is an example of active transport.
- C.Water moves across plasma membrane by active transport.
- D.Facilitated transport requires assistance of carrier proteins.
Show answer
In facilitated transport, molecules cross the membrane with the help of membrane proteins, while still moving down their concentration gradient.
Read the full explanation →Who among the following has coined the term 'Quark', the fundamental particles that make up protons and neutrons in an atomic nucleus ?
- A.Richard Feynman
- B.Murray Gell-Mann
- C.Albert Einstein
- D.Niels Bohr
Show answer
The American physicist Murray Gell-Mann proposed quarks in 1964 and gave them their name. Gell-Mann, and independently George Zweig, suggested that protons, neutrons and other such particles are built from smaller units.
Read the full explanation →The spindle fibre is attached to which of the following specific regions of the chromosomes?
- A.Kinetochore
- B.Chromonema
- C.Telomere
- D.Centriole
Show answer
Spindle fibres attach to the kinetochore, a disc-shaped protein structure on the centromere of each chromosome. During cell division the spindle, made of microtubules, pulls the copies of each chromosome apart.
Read the full explanation →