Biology Concepts MCQs for UPSC Prelims

Correct answer: A - Nitric oxide

Nitric oxide is produced naturally in the human body and acts as a signalling molecule that relaxes the smooth muscle of blood vessel walls, causing vasodilation and increased blood flow, so option (a) is correct. Nitrous oxide is an anaesthetic and greenhouse gas, not a vasodilator synthesised for this role. Nitrogen dioxide and nitrogen pentoxide are toxic air pollutants, not physiological signalling molecules. Hence nitric oxide is the answer.

Correct answer: C - 1 and 3 only

Statements 1 and 3 are correct: vegetative propagation produces genetically identical clonal populations and can be carried out through most of the year. Statement 2 is wrong because ordinary vegetative propagation tends to transmit, not eliminate, viruses (virus elimination requires specialised meristem-tip culture). Hence 1 and 3 only.

Correct answer: C - rate of respiration is decreased

Even after harvest, fruits continue to respire, consuming their stored sugars and ripening, which eventually leads to spoilage. Cold storage lowers the temperature, which slows down the metabolic rate of respiration (and microbial/enzyme activity), thereby delaying ripening and decay and extending storage life. Preventing sunlight, increasing carbon dioxide artificially, or raising humidity are not the primary reason behind ordinary cold storage. Hence the reduced rate of respiration is the correct explanation.

Correct answer: B - 2 and 3 only

Multi-drug resistance develops in the pathogens themselves, mainly because of misuse of antibiotics. Taking incorrect or incomplete doses lets resistant microbes survive and multiply (statement 2), and the widespread use of antibiotics in livestock farming drives resistance that can spread to humans (statement 3). The genetic predisposition of people and the presence of multiple chronic diseases relate to a person's vulnerability, not to the development of resistance in the microbes, so statements 1 and 4 are wrong. Hence 2 and 3 only is correct.

Correct answer: B - The gum made from its seeds is used in the extraction of shale gas

The gum made from cluster bean (guar) seeds is used in hydraulic fracturing to help extract shale gas, which drove a surge in guar cultivation and exports. Option (a) is wrong as guar is not a feedstock for biodegradable plastics, option (c) is wrong as it is not noted for antihistamine leaf extracts, and option (d) is wrong as guar is not a biodiesel source. Hence the gum is used in shale gas extraction.

Correct answer: B - Carbon, Hydrogen, Nitrogen

Life is built on organic molecules such as proteins, nucleic acids, carbohydrates and lipids, whose backbones are made chiefly of carbon, hydrogen, nitrogen (and oxygen). Carbon's ability to form long chains, together with hydrogen and nitrogen, made the assembly of amino acids and nucleotides possible in the primitive environment, so option (b) is the best set. The other options include sodium, calcium, phosphorus or potassium, which though biologically useful are not the primary structural elements that gave rise to the first organic molecules of life, so they are incorrect.

Correct answer: C - most of the root hairs are lost during transplantation

Root hairs are delicate, thread-like extensions of root cells that vastly increase the surface area for absorbing water and minerals. During transplantation these fragile root hairs are easily torn off, so the seedling cannot absorb enough water and nutrients and may wilt or die. The new soil's mineral content is usually adequate, root hairs do not 'grip too hard,' and leaf damage is not the principal cause. Hence the loss of root hairs during transplantation is the correct reason.

Correct answer: C - moulds

Aflatoxins are produced by moulds (fungi) of the genus Aspergillus, chiefly Aspergillus flavus and Aspergillus parasiticus, which grow on improperly stored cereals and oilseeds, so option (c) is correct. They are not produced by bacteria, protozoa or viruses, so options (a), (b) and (d) are wrong.