Biology Questions and Answers

Answer: C

The common feature is the presence of nucleic acid.

The nucleus holds the cell's chromosomal DNA, and both chloroplasts and mitochondria contain their own circular DNA and ribosomes, a sign of their origin from free-living bacteria (the endosymbiont theory). All three also contain RNA.

Lamellae (thylakoids) are found only in chloroplasts, cristae only in mitochondria, and the nucleolus only in the nucleus, so none of them is common to all three.

Answer: B

They are called ergastic substances.

Ergastic substances are non-living, metabolically inactive products of the cell that accumulate in the cytoplasm or vacuoles: reserve food such as starch grains, oil drops and protein bodies, secretions, and excretory products such as crystals of calcium oxalate (raphides) and tannins.

Reserve materials, secretory substances and crystals are therefore each just one kind of ergastic substance; the collective term for all such inactive inclusions is 'ergastic substances'.

Answer: D

The social insect is the termite.

Termites live in large colonies with division of labour among castes: a king and queen that reproduce, workers that build and forage, and soldiers that defend the mound. Such cooperative colony life with overlapping generations is what makes an insect 'social' (eusocial), like ants and honeybees.

Mosquitoes and bedbugs live and feed as individuals. Locusts gather into huge swarms, but a swarm has no castes or cooperative brood care, so locusts are gregarious rather than social.

Answer: B

Only pair II is wrongly matched, so the answer is II only.

Prolactin is secreted by the anterior pituitary, not the adrenal medulla. It stimulates milk production after childbirth. The adrenal medulla secretes adrenaline and noradrenaline.

The other pairs are correct. Testosterone is secreted by the interstitial (Leydig) cells of the testis, estrogen mainly by the ovarian follicles, and progesterone by the corpus luteum.

Answer: C

The antibiotic that prevents cell wall synthesis is penicillin.

Penicillin, discovered by Alexander Fleming in 1928, blocks the enzymes (transpeptidases) that cross-link peptidoglycan in the bacterial cell wall. The weakened wall bursts under osmotic pressure, killing the bacterium. Human cells have no cell wall, which is why penicillin is relatively safe.

Rifampicin inhibits bacterial RNA polymerase, streptomycin blocks protein synthesis on the ribosome, and anthracyclines are anticancer drugs that act on DNA.

Answer: A

Whooping cough is caused by the bacterium Bordetella pertussis, option A.

Diphtheria antitoxin is a treatment, Streptococcal pneumonia causes a lung infection, and Salmonella paratyphi causes paratyphoid fever.

Whooping cough, or pertussis, is a highly contagious respiratory disease of children, and it is prevented by the DPT vaccine in which the P stands for pertussis. The diphtheria antitoxin is used against diphtheria, and Streptococcus pneumoniae causes pneumonia, while Salmonella paratyphi causes enteric fever.

Answer: C

Plants that do best in low light are called sciophytes (shade-loving plants), option C.

Heliophytes love strong sunlight, halophytes grow in salty soil, and sporophytes are the spore-producing stage of the plant life cycle.

The word sciophyte comes from the Greek skia, meaning shadow, and these plants are found in the forest floor or in shade, where they photosynthesise at low light levels. Heliophytes are sun plants, halophytes live in saline soils, and sporophytes are not an ecological group of plants at all.

Answer: B

The Mantoux test is a skin test used to identify tuberculosis infection, option B.

Malaria is diagnosed by blood smear, cancer by biopsy and imaging, and diphtheria by the Schick test or throat swab.

In the Mantoux test, a small amount of tuberculin protein is injected under the skin of the forearm, and the size of the raised area after 48 to 72 hours shows whether the person has been exposed to the tuberculosis bacterium. It is not used for malaria, cancer or diphtheria.

Answer: C

The matching is Insulin with Diabetes Mellitus (5), Thyroxine with Goitre (4), Glucocorticoids with Cushing's syndrome (1) and Growth hormone with Acromegaly (3), which is the code 5 4 1 3.

Insulin deficiency causes diabetes mellitus. A thyroxine-related disorder of the gland shows as goitre. Excess glucocorticoid (cortisol) causes Cushing's syndrome, and excess growth hormone in adults causes acromegaly. Diabetes insipidus (2) belongs to the antidiuretic hormone, which is not in the list, so every code that places 2 against a hormone here is wrong.

Answer: C

Statements (2) and (3) are correct. Chlorophyll a is C₅₅H₇₂O₅N₄Mg and chlorophyll b, which has a formyl group in place of a methyl group, is C₅₅H₇₀O₆N₄Mg, exactly as the question prints them.

(1) is wrong because a carotenoid is a C₄₀ hydrocarbon pigment with no magnesium, and (4) is wrong because xanthophylls are oxygenated carotenoids, also magnesium-free. Any option containing (1) or (4) is therefore rejected.

Magnesium sits at the centre of the porphyrin ring of both chlorophylls, which is why Mg appears in each formula, while the carotenoids and xanthophylls are accessory pigments that contain only carbon, hydrogen and (for xanthophylls) oxygen.