UPSC Prelims 2011 Science and Technology questions: topic-wise weightage
UPSC Prelims 2011 asked 17 science and technology questions in GS Paper I, spread over 3 topics. See the science and technology weightage for 2011 below, then attempt each question with the official answer and an explanation.
Science and Technology 2011: questions by topic
- Biology, health and biotechnology7
- Space technology5
- Physics and chemistry in daily life; energy and nuclear technology5
Counted from the 17 questions on this page, tagged by topic in the Battle IAS PYQ bank.
Seeing 17 Science and Technology questions spread over 3 topics can feel overwhelming. That's exactly why the Battle IAS PYQ Book maps every question topic by topic, so you know what to study first. Download free sample
Biology, health and biotechnology 7
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.
Space technology 5
Satellites used for telecommunication relay are kept in a geostationary orbit. A satellite is said to be in such an orbit when :
- 1. The orbit is geosynchronous.
- 2. The orbit is circular.
- 3. The orbit lies in the plane of the Earth’s equator.
- 4. The orbit is at an altitude of 22,236 km.
Select the correct answer using the codes given below :
Answer (a) & explanation
Statements 1, 2 and 3 are correct (a). A geostationary orbit is a special geosynchronous orbit: the satellite completes one revolution in one sidereal day (about 23 h 56 min) (1). It must be circular (2) and lie in the plane of the equator (3), moving west to east, so it appears fixed above one spot. Statement 4 is wrong: the altitude is about 35,786 km, which is 22,236 miles, not 22,236 km. So options (b), (c) and (d) fail.
Notice the difference: every geostationary orbit is geosynchronous, but a geosynchronous orbit can be inclined or elliptical and then traces a figure-of-eight. India's GSAT and INSAT satellites use GEO, launched on the GSLV and LVM3. The NavIC system uses both geostationary and inclined geosynchronous satellites. Trap: the number 22,236 is right only in miles.
Answer as per the official UPSC answer key.
What is the difference between Bluetooth and Wi-Fi devices ?
Answer (a) & explanation
Option (a) is correct. Bluetooth works in the 2.4 GHz band for short-range personal area networks (PAN), linking devices a few metres apart. Wi-Fi uses 2.4 GHz or 5 GHz (and newer 6 GHz in Wi-Fi 6E/7) for wireless local area networks. (b) is wrong: Bluetooth is not a WLAN technology, and Wi-Fi is a LAN, not a wide-area, technology. (c) is wrong: neither needs line of sight; radio waves pass through walls, unlike infrared remotes. (d) fails because (b) is wrong.
Notice the wider idea: India delicensed the lower 6 GHz band (5925–6425 MHz) for Wi-Fi in 2025. Bluetooth is named after the Danish king Harald Bluetooth. Trap: line of sight belongs to infrared, not Bluetooth.
Answer as per the official UPSC answer key.
A new optical disc format known as the Blu-ray Disc (BD) is becoming popular. In what way is it different from the traditional DVD ?
- 1. DVD supports Standard Definition video while BD supports High Definition video.
- 2. Compared to a DVD, the BD format has several times more storage capacity.
- 3. Thickness of BD is 2.4 mm while that of DVD is 1.2 mm.
Which of the statements given above is/are correct ?
Answer (b) & explanation
Statements 1 and 2 are correct (b). A Blu-ray disc is read by a blue-violet laser (405 nm) with a shorter wavelength than a DVD's red laser, so data packs more tightly: about 25 GB per layer against 4.7 GB on a DVD. That gives several times more storage (2) and room for High Definition video, while DVD is mainly standard definition (1). Statement 3 is wrong: both discs are 1.2 mm thick; Blu-ray's data layer just sits nearer the surface. So (a), (c) and (d) fail.
Notice the trend: Ultra HD Blu-ray stores up to 100 GB for 4K video, but streaming has largely replaced discs. Trap: '2.4 mm' doubles the real thickness.
Answer as per the official UPSC answer key.
What is the difference between asteroids and comets ?
- 1. Asteroids are small rocky planetoids, while comets are formed of frozen gases held together by rocky and metallic material.
- 2. Asteroids are found mostly between the orbits of Jupiter and Mars, while comets are found mostly between Venus and Mercury.
- 3. Comets show a perceptible glowing tail, while asteroids do not.
Which of the statements given above is/are correct ?
Answer (b) & explanation
Statements 1 and 3 are correct (b). Asteroids are small rocky or metallic bodies, while comets are 'dirty snowballs' of frozen gases, ice and dust held with rock (1). Near the Sun, a comet's ice vaporises and forms a glowing coma and tail pointing away from the Sun, while asteroids show no tail (3). Statement 2 is wrong: asteroids are mostly in the belt between Mars and Jupiter, but comets come from the distant Kuiper Belt and Oort Cloud, not between Venus and Mercury. So (a), (c) and (d) fail.
Notice the missions: NASA's DART (2022) changed an asteroid's orbit, OSIRIS-REx returned Bennu samples (2023), and the interstellar comet 3I/ATLAS was seen in 2025. Trap: statement 2 puts comets in the inner solar system.
Answer as per the official UPSC answer key.
What is “Virtual Private Network” ?
Answer (b) & explanation
Option (b) is correct. A Virtual Private Network builds a secure, encrypted 'tunnel' over the public internet, so a remote user can reach the office network as if sitting inside it, while the data stay private. (a) is wrong: a VPN does not need a private network; its point is to use the public internet safely. (c) is wrong: it describes cloud computing, where users share computing resources from a provider. (d) fails because (b) is correct.
Notice the policy angle: CERT-In's 2022 directions require VPN providers in India to keep user records for five years, which led some foreign providers to remove Indian servers. VPNs also let users hide their location. Trap: (a) sounds similar but misses the 'public internet' part.
Answer as per the official UPSC answer key.
Physics and chemistry in daily life; energy and nuclear technology 5
Microbial fuel cells are considered a source of sustainable energy. Why ?
- 1. They use living organisms as catalysts to generate electricity from certain substrates.
- 2. They use a variety of inorganic materials as substrates.
- 3. They can be installed in waste water treatment plants to cleanse water and produce electricity.
Which of the statements given above is/are correct ?
Answer (c) & explanation
Statements 1 and 3 are correct (c). A microbial fuel cell uses living bacteria as catalysts to break down substrates and release electrons, which flow through a circuit as electric current (1). It can be fitted in wastewater treatment plants, where bacteria feed on organic matter in sewage, cleaning the water while generating electricity (3). Statement 2 is wrong: the substrates are mainly organic materials such as glucose, acetate and sewage waste, not a variety of inorganic materials. So options (a), (b) and (d) fail.
Notice why it is called sustainable: it turns waste into power, works at normal temperatures, and does not burn fuel. Related ideas include biogas from anaerobic digestion and bio-electrochemical systems. India's SATAT and GOBARdhan schemes also aim at waste-to-energy. Trap: 'living organisms' in statement 1 is correct, since bacteria are the catalysts, not an error.
Answer as per the official UPSC answer key.
The function of heavy water in a nuclear reactor is to
Answer (a) & explanation
Slowing down neutrons is correct (a). Heavy water (D₂O) is a moderator. Fast neutrons released in fission are too quick to be captured by uranium-235; colliding with deuterium nuclei slows them to thermal speed so they cause further fission and sustain the chain reaction. Heavy water absorbs few neutrons, so it lets reactors run on natural uranium. (b) is the opposite. (c) is incomplete: heavy water also serves as coolant in India's PHWRs, but its defining function asked here is moderation. (d) is wrong: control rods of boron or cadmium absorb neutrons to slow or stop the reaction.
Notice India's fleet: most Indian reactors are Pressurised Heavy Water Reactors, matching stage one of the three-stage programme.
Answer as per the official UPSC answer key.
The surface of a lake is frozen in severe winter, but the water at its bottom is still liquid. What is the reason ?
Answer (c) & explanation
Density of water is maximum at 4°C is correct (c). As a lake cools in winter, surface water reaches 4°C, becomes densest and sinks. Colder water then stays on top and freezes, and ice floats because it is lighter than water. So the bottom stays liquid at about 4°C, and fish survive. (a) is a helping factor, since ice is a poor conductor and insulates the water below, but it is not the basic reason. (b) is wrong: heat is lost from the surface, which is why it freezes. (d) fails because (c) is correct.
Notice the wider idea: this anomalous expansion of water between 0°C and 4°C is unusual among liquids. It also makes water pipes burst in frost and helps break rocks (frost weathering).
Answer as per the official UPSC answer key.
What is the difference between a CFL and an LED lamp ?
- 1. To produce light, a CFL uses mercury vapour and phosphor while an LED lamp uses semi-conductor material.
- 2. The average life span of a CFL is much longer than that of an LED lamp.
- 3. A CFL is less energy-efficient as compared to an LED lamp.
Which of the statements given above is/are correct ?
Answer (c) & explanation
Statements 1 and 3 are correct (c). A CFL passes current through mercury vapour, whose ultraviolet light makes a phosphor coating glow, while an LED emits light from a semiconductor chip (1). LEDs give more light per watt, so a CFL is less energy-efficient (3). Statement 2 is reversed: an LED lasts much longer, about 25,000 hours or more, against roughly 8,000 for a CFL. So (a), (b) and (d) fail.
Notice the policy: India's UJALA scheme (2015) distributed over 36 crore LED bulbs, cutting their price sharply, and the Street Lighting National Programme replaced street lamps with LEDs. CFLs also pose a mercury disposal problem. The 2014 Nobel Prize in Physics went for the blue LED.
Answer as per the official UPSC answer key.
An artificial satellite orbiting around the Earth does not fall down. This is so because the attraction of Earth
Answer (d) & explanation
Option (d) is correct. A satellite is always 'falling' towards Earth, but it moves sideways so fast that it keeps missing it. Earth's gravity supplies the centripetal acceleration that bends its straight path into a circle. (a) is wrong: gravity certainly exists in orbit; at the ISS height it is still about 90% of surface gravity. (b) is wrong: the Moon's pull is tiny and does not cancel Earth's. (c) is wrong: gravity provides acceleration towards the centre, not the forward speed; the speed comes from the launch.
Notice the numbers: a low Earth orbit needs about 7.8 km/s; a geostationary satellite at about 35,786 km circles once in 24 hours. Astronauts float because they are in free fall, not because gravity is absent.
Answer as per the official UPSC answer key.
All years by topic
Every question from 2011 to 2026, grouped by syllabus topic, with year-wise trends.