Biology, health and biotechnology: previous-year questions
68 real UPSC Prelims questions (2011–2026) with the official answer and a clear explanation. 12 of them came in the last five papers.
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Which one of the following sets of elements was primarily responsible for the origin of life on the Earth?
Answer (b) & explanation
Carbon, hydrogen and nitrogen is correct (b). Life's building blocks, amino acids, sugars, fats and nucleic acids, are made mainly of carbon, hydrogen, nitrogen and oxygen, with phosphorus and sulphur. The Miller–Urey experiment (1953) made amino acids by passing sparks through methane, ammonia, hydrogen and water, mimicking the early Earth. (a) and (d) are wrong: sodium and potassium are minerals important for cells but not the core of organic molecules. (c) is wrong: calcium is not primary, and the early atmosphere had little free oxygen.
Notice the related theories: Oparin–Haldane's 'primordial soup', the RNA world, and life near deep-sea hydrothermal vents. Oxygen built up later through cyanobacteria in the Great Oxidation Event (about 2.4 billion years ago). Trap: oxygen is essential now but was not primary then.
Answer as per the official UPSC answer key.
At present, scientists can determine the arrangement or relative positions of genes or DNA sequences on a chromosome. How does this knowledge benefit us ?
- 1. It is possible to know the pedigree of livestock.
- 2. It is possible to understand the causes of all human diseases.
- 3. It is possible to develop disease-resistant animal breeds.
Which of the statements given above is/are correct ?
Answer (c) & explanation
Statements 1 and 3 are correct (c). Gene mapping finds the positions of genes and DNA markers on chromosomes. This helps confirm the pedigree or parentage of livestock through DNA markers (1). It also helps breeders identify genes for traits such as disease resistance and use marker-assisted selection to develop resistant breeds (3). Statement 2 is wrong because of the word 'all': many diseases come from germs, diet, environment or injury, so gene maps cannot explain every human disease. So options (a), (b) and (d) fail.
Notice the bigger picture: the Human Genome Project finished in 2003, and India's Genome India Project released data from 10,000 genomes in 2025. Genome mapping also supports gene therapy, such as India's first CRISPR-based sickle cell research, and precision medicine. Trap: absolute words like 'all' make a statement suspect.
Answer as per the official UPSC answer key.
When the bark of a tree is removed in a circular fashion all around near its base, it gradually dries up and dies because
Answer (b) & explanation
The answer is (b). Removing a ring of bark all round the trunk is called girdling or ringing. The bark contains the phloem, which carries sugars made in the leaves down to the roots. Once the phloem is cut, the roots no longer get food, so they gradually starve of energy, stop absorbing water and minerals, and the tree dries up and dies. Option (a) is wrong because water rises through the xylem in the inner wood, which girdling leaves intact, so the leaves stay green for some time. Options (c) and (d) are not the main reason.
Notice the classic experiment: in girdling, the bark just above the ring swells, because food carried down by the phloem piles up there. This proves the phloem carries food downwards. Xylem carries water up, mainly pulled by transpiration. Trap: water still reaches the leaves; it is the roots that starve.
Answer as per the official UPSC answer key.
A genetically engineered form of brinjal, known as the Bt-brinjal, has been developed. The objective of this is
Answer (a) & explanation
To make it pest-resistant is correct (a). Bt brinjal carries the cry1Ac gene from the soil bacterium Bacillus thuringiensis. The gene makes a protein toxic to the fruit and shoot borer, the main pest of brinjal, so farmers need fewer insecticide sprays. (b) is wrong: the change does not target taste or nutrition. (c) is wrong: drought tolerance needs other genes. (d) is wrong: longer shelf life was the aim of the 'Flavr Savr' tomato, not Bt brinjal.
Notice the policy story: GEAC cleared Bt brinjal in 2009, but the environment ministry imposed a moratorium in February 2010, which still holds; Bangladesh grows it. Bt cotton (2002) remains India's only commercial GM crop, while GM mustard DMH-11 awaits final clearance.
Answer as per the official UPSC answer key.
A company marketing food products advertises that its items do not contain trans-fats. What does this campaign signify to the customers ?
- 1. The food products are not made out of hydrogenated oils.
- 2. The food products are not made out of animal fats/oils.
- 3. The oils used are not likely to damage the cardiovascular health of the consumers.
Which of the statements given above is/are correct ?
Answer (c) & explanation
Statements 1 and 3 are correct (c). Trans fats form mainly when vegetable oil is partially hydrogenated, as in vanaspati, so 'no trans fat' signals no such oils (1). Trans fats raise 'bad' LDL cholesterol and lower 'good' HDL, so avoiding them protects the heart (3). Statement 2 is wrong: the claim says nothing about animal fats; ghee and butter may still be used, and they carry a little natural trans fat. So (a), (b) and (d) fail.
Notice the policy: FSSAI capped industrial trans fat at 2% of total fat in oils and foods from January 2022, in line with the WHO's 'REPLACE' goal. Trap: 'no trans fat' is not the same as 'no saturated or animal fat'.
Answer as per the official UPSC answer key.
Aspartame is an artificial sweetener sold in the market. It consists of amino acids and provides calories like other amino acids. Yet, it is used as a low-calorie sweetening agent in food items. What is the basis of this use ?
Answer (d) & explanation
Option (d) is correct. Aspartame, made of two amino acids, gives about 4 kcal per gram, the same as sugar, but it is about 200 times sweeter. So only a tiny amount is needed, and the food ends up with very few calories. (a) is wrong: it is not as sweet as sugar, and the body does digest and oxidise it. (b) is wrong: processing does not make it resistant to oxidation; in fact it breaks down with heat. (c) is wrong: its metabolites do yield calories.
Notice the debate: the WHO's cancer agency (IARC) classed aspartame as 'possibly carcinogenic' in 2023, but JECFA kept the safe daily intake at 40 mg/kg body weight. People with phenylketonuria must avoid it.
Answer as per the official UPSC answer key.
A married couple adopted a male child. A few years later, twin boys were born to them. The blood group of the couple is AB positive and O negative. The blood group of the three sons is A positive, B positive, and O positive. The blood group of the adopted son is
Answer (a) & explanation
O positive is correct (a). An AB parent passes either A or B, and an O parent passes only O. So the couple's own children can only be A (genotype AO) or B (genotype BO); an O child is impossible. The twins must be the A positive and B positive sons, and the O positive son must be adopted. (b) and (c) are the twins' groups. (d) is wrong: the data are enough to decide.
Notice the Rh factor: the O parent is Rh negative, the AB parent positive, so Rh-positive children are possible and do not change the answer. Another rule: AB is the universal recipient and O negative the universal donor. Trap: the Rh signs are a distraction.
Answer as per the official UPSC answer key.
Regular intake of fresh fruits and vegetables is recommended in the diet since they are a good source of antioxidants. How do antioxidants help a person maintain health and promote longevity ?
Answer (c) & explanation
They neutralise free radicals is correct (c). Normal metabolism, pollution and smoking produce free radicals, unstable molecules with an unpaired electron that damage cell membranes, proteins and DNA, and are linked to ageing, heart disease and cancer. Antioxidants such as vitamins C and E, beta-carotene and plant polyphenols donate electrons and neutralise them. (a) is wrong: antioxidants do not activate enzymes for vitamin synthesis. (b) is wrong: oxidation of food is how we get energy; it is not wasteful. (d) is wrong: they are not mainly gene activators.
Notice the related idea: this damage is called oxidative stress. Large trials show antioxidant supplements give little benefit, while whole fruits and vegetables do. Trap: (b) misreads 'oxidation' as bad in general.
Answer as per the official UPSC answer key.