Biology Questions and Answers

Answer: B

The products are carbon dioxide and ethanol (2 and 4 only).

In plants and in yeast, anaerobic respiration (fermentation) breaks glucose down without oxygen into ethanol and carbon dioxide, releasing a little energy:

\[ \begin{aligned} &\mathrm{C_{6}H_{12}O_{6}} \\ &\mathrm{\rightarrow 2C_{2}H_{5}OH + 2CO_{2}} \end{aligned} \]

Lactic acid is the product of anaerobic respiration in animal muscle, and water is produced only in aerobic respiration, when oxygen is the final electron acceptor. That rules out options containing 1 or 3.

Answer: B

The exception is the Tetanus vaccine.

The tetanus vaccine is a toxoid: it contains the tetanus toxin made harmless by chemical treatment, not the bacterium itself. It teaches the body to neutralise the toxin, which is what causes the disease.

The other three are whole-pathogen vaccines. The rabies vaccine and the hepatitis A vaccine contain inactivated (killed) virus, and the oral polio vaccine contains live attenuated (weakened) poliovirus.

Answer: C

The one that is not a cow breed is Surti.

Surti is a breed of buffalo from Gujarat (the name is also used for a goat breed). It is not a cattle breed.

The other three are Indian cattle breeds. Gir is a famous dairy breed from the Gir forest area of Gujarat. Tharparkar is a dual-purpose breed from the Thar desert of Rajasthan. Mewati, also called Kosi, is a draught and dairy breed from the Mewat region of Haryana and Rajasthan.

Answer: C

The Commission's answer is Iris is unable to dilate the pupil immediately.

In bright light the iris keeps the pupil small to limit the light entering the eye. On moving into a dark room, the iris muscles must relax the iris to widen the pupil and let in more light, and this takes a little time, so vision is poor at first. This is the textbook explanation the paper follows. (The retina also takes time to adapt to the dark, which is why full night vision takes much longer.)

The distance between lens and retina never changes; the eye focuses by changing the lens's curvature. The retina does not become insensitive, and 'unable to adjust itself' is too vague to be the reason.

Answer: C

Bats fly in the dark because they are guided by ultrasonic waves produced by them.

This is echolocation. A bat emits high-frequency sound pulses, well above the range of human hearing, and listens for the echoes from obstacles and prey. From the delay and direction of the echoes it judges distance and position, so it can navigate and hunt in complete darkness.

Bats do not rely on vision in the dark, and many species have small eyes, so better night vision and large pupils are not the reason. 'Any bird can do so' is simply false: bats are mammals, and most birds cannot fly blind.

Answer: A

Agar is obtained from algae.

Agar is a jelly-like polysaccharide extracted from the cell walls of red algae (seaweeds) such as Gelidium and Gracilaria. It sets into a firm gel that microbes cannot digest easily, which makes it the standard culture medium in laboratories; it is also used as a thickener in ice creams, jellies and bakery products.

Mosses are bryophytes, and Cycas and pine are gymnosperms. None of them is a source of agar.

Answer: D

All four can donate, so the answer is 1, 2, 3 and 4.

A person of group AB has both A and B antigens on his red cells and therefore neither anti-A nor anti-B antibodies in his plasma. Red cells of group A, B, AB or O will not be attacked, which is why AB is called the universal recipient.

So the wife (A), son (AB), friend (O) and daughter (B) are all compatible. Only 2, or 2 and 4, or 1, 2 and 4, each leave out a donor whose blood the man can receive; leaving out the friend is the most surprising, since group O is the universal donor.

Answer: A

The correct matching is A-2, B-1, C-3.

Leprosy is caused by the bacterium Mycobacterium leprae. Rabies is caused by a virus (a lyssavirus) passed on by the bite of an infected animal. Malaria is caused by the protozoan Plasmodium, carried by the female Anopheles mosquito.

The option A-1, B-2, C-3 swaps leprosy and rabies, making rabies bacterial. The other two put malaria with bacteria or viruses, which is the one pairing most candidates know well.

Answer: C

The keyed answer is 1, 3 and 4 only (tonsils, appendix, external ears).

The vermiform appendix and the external ear, with the small muscles that once moved it, are standard textbook examples of vestigial structures in humans. Tonsils appear in the same older textbook lists, although they are now known to have an immune function, so the key follows the traditional textbook classification.

Intestinal villi are not vestigial: they provide the large surface area for absorbing digested food. Nails protect the fingertips and help in handling objects. Every option that includes villi or nails is therefore wrong, which leaves 1, 3 and 4.

Answer: C

The statements are True, False, True.

1. True: diphtheria is caused by the bacterium Corynebacterium diphtheriae, while polio, rabies and influenza are viral.
2. False: kala-azar is covered by the National Vector Borne Disease Control Programme, along with malaria, dengue, chikungunya, Japanese encephalitis and lymphatic filariasis. The odd one out is polio, which is not vector-borne.
3. True: diabetes is a non-communicable disease, while tuberculosis, HIV/AIDS and influenza are infectious.

So only option c, True False True, fits.