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Biology

Class 12 · Science & Environment

Real UPSC Prelims questions from 2016–2026, linked to this book. Try each one first, then open the answer. 2026 answers follow UPSC's provisional answer key.

A question can draw on more than one chapter, so the chapter counts add up to more than 21.

Ch 5 · Molecular Basis of Inheritance

Prelims 2016 · Q59

Which of the following statements is/are correct?

Viruses can infect

  1. 1.bacteria
  2. 2.fungi
  3. 3.plants

Select the correct answer using the code given below.

  1. (a)1 and 2 only
  2. (b)3 only
  3. (c)1 and 3 only
  4. (d)1, 2 and 3
Show answer

UPSC's answer: (d)

NCERT answers it: Class 12 Biology, Ch 5 (Molecular Basis of Inheritance); Class 12 Biology, Ch 8 (Microbes in Human Welfare).

The one fact NCERT doesn't give: Some viruses, called mycoviruses, infect fungi.

Class 12 Biology: bacteriophages are viruses that infect bacteria (ch 5), and ch 8 names plant viruses. With the fact, all three are true. Answer (d).

Hindi version: UPSC's official question paper (2016), question 59 ↗

Prelims 2023 · Q70

'Microsatellite DNA' is used in the case of which one of the following?

  1. (a)Studying the evolutionary relationships among various species of fauna
  2. (b)Stimulating 'stem cells' to transform into diverse functional tissues
  3. (c)Promoting clonal propagation of horticultural plants
  4. (d)Assessing the efficacy of drugs by conducting series of drug trials in a population
Show answer

UPSC's answer: (a)

NCERT answers it: Class 12 Biology, Ch 5 (Molecular Basis of Inheritance).

How to solve it with NCERT: Class 12 Biology, ch 5: microsatellites are repetitive DNA sequences used in determining population and genetic diversities. Of the options, only (a) is about comparing the genes of living things. Answer (a).

Hindi version: UPSC's official question paper (2023), question 70 ↗

Prelims 2025 · Q49

Consider the following statements:

  1. I.No virus can survive in ocean waters.
  2. II.No virus can infect bacteria.
  3. III.No virus can change the cellular transcriptional activity in host cells.

How many of the statements given above are correct?

  1. (a)Only one
  2. (b)Only two
  3. (c)All the three
  4. (d)None
Show answer

UPSC's answer: (d)

NCERT answers it: Class 12 Biology, Ch 5 (Molecular Basis of Inheritance).

The one fact NCERT doesn't give: Seawater holds huge numbers of viruses, so statement I is false as well.

Class 12 Biology, ch 5: bacteriophages are viruses that infect bacteria (II false). An infected bacterium makes virus particles from the viral genes as if they were its own, so the virus changes its host's activity (III false). With the fact, none is correct. Answer (d).

Hindi version: UPSC's official question paper (2025), question 49 ↗

Ch 7 · Human Health and Disease

Prelims 2019 · Q100

Which one of the following statements is not correct?

  1. (a)Hepatitis B virus is transmitted much like HIV.
  2. (b)Hepatitis B, unlike Hepatitis C, does not have a vaccine.
  3. (c)Globally, the number of people infected with Hepatitis B and C viruses are several times more than those infected with HIV.
  4. (d)Some of those infected with Hepatitis B and C viruses do not show the symptoms for many years.
Show answer

UPSC's answer: (b)

NCERT answers it: Class 12 Biology, Ch 7 (Human Health and Disease).

Class 12 Biology, ch 7: a hepatitis B vaccine is produced from yeast. So (b), which says hepatitis B has no vaccine, is the incorrect statement. Answer (b).

Beyond NCERT: it is hepatitis C that has no vaccine; antiviral medicines can cure it. Source: WHO fact sheet, Hepatitis C, who.int

Hindi version: UPSC's official question paper (2019), question 100 ↗

Prelims 2021 · Q65

With reference to recent developments regarding 'Recombinant Vector Vaccines', consider the following statements:

  1. 1.Genetic engineering is applied in the development of these vaccines.
  2. 2.Bacteria and viruses are used as vectors.

Which of the statements given above is/are correct?

  1. (a)1 only
  2. (b)2 only
  3. (c)Both 1 and 2
  4. (d)Neither 1 nor 2
Show answer

UPSC's answer: (c)

NCERT answers it: Class 12 Biology, Ch 7 (Human Health and Disease); Class 12 Biology, Ch 9 (Biotechnology: Principles and Processes).

How to solve it with NCERT: Class 12 Biology, ch 7: recombinant DNA technology makes pathogens' antigen proteins in bacteria or yeast for vaccines — genetic engineering (1). Ch 9: Agrobacterium, a bacterium, and disarmed retroviruses are used as vectors to deliver genes (2). Answer (c).

Beyond NCERT: a recombinant vector vaccine uses a harmless virus or bacterium as a carrier (vector) to take a disease-causing agent's genetic material into our cells. Source: NIAID (US National Institutes of Health), 'Vaccine Types', niaid.nih.gov (content last reviewed July 2019)

Hindi version: UPSC's official question paper (2021), question 65 ↗

Prelims 2021 · Q70

Consider the following statements:

  1. 1.Adenoviruses have single-stranded DNA genomes whereas retroviruses have double-stranded DNA genomes.
  2. 2.Common cold is sometime caused by an adenovirus whereas AIDS is caused by a retrovirus.

Which of the statements given above is/are correct?

  1. (a)1 only
  2. (b)2 only
  3. (c)Both 1 and 2
  4. (d)Neither 1 nor 2
Show answer

UPSC's answer: (b)

NCERT answers it: Class 12 Biology, Ch 8 (Microbes in Human Welfare); Class 12 Biology, Ch 7 (Human Health and Disease).

Class 12 Biology: retroviruses have an RNA genome (ch 7), so 1 is false. Adenovirus causes respiratory infections (ch 8), and HIV, which causes AIDS, is a retrovirus (ch 7), so 2 is true. Answer (b).

Beyond NCERT: adenoviruses in fact have double-stranded DNA genomes, while retroviruses carry RNA. So statement 1 gets both viruses wrong. Source: Gu et al., 'Molecular characterization and evolutionary analysis of human adenovirus type 55', Virus Genes (2025), on PubMed Central (US National Library of Medicine), PMC12263808

Hindi version: UPSC's official question paper (2021), question 70 ↗

Prelims 2022 · Q97

Which one of the following statements best describes the role of B cells and T cells in the human body?

  1. (a)They protect the body from environmental allergens.
  2. (b)They alleviate the body's pain and inflammation.
  3. (c)They act as immunosuppressants in the body.
  4. (d)They protect the body from the diseases caused by pathogens.
Show answer

UPSC's answer: (d)

NCERT answers it: Class 12 Biology, Ch 7 (Human Health and Disease).

Class 12 Biology, ch 7: our immune responses are carried out by B-lymphocytes and T-lymphocytes; B-lymphocytes produce antibodies against pathogens, helped by T-cells. So they protect the body from diseases caused by pathogens. Answer (d).

Hindi version: UPSC's official question paper (2022), question 97 ↗

Ch 8 · Microbes in Human Welfare

Prelims 2017 · Q59

Biological Oxygen Demand (BOD) is a standard criterion for

  1. (a)Measuring oxygen levels in blood
  2. (b)Computing oxygen levels in forest ecosystems
  3. (c)Pollution assay in aquatic ecosystems
  4. (d)Assessing oxygen levels in high altitude regions
Show answer

UPSC's answer: (c)

NCERT answers it: Class 12 Biology, Ch 8 (Microbes in Human Welfare).

Class 12 Biology, ch 8: BOD is the oxygen that bacteria would use to break down all the organic matter in a litre of water. So it measures organic matter: the higher the BOD of waste water, the more it pollutes. Answer (c).

Hindi version: UPSC's official question paper (2017), question 59 ↗

Prelims 2021 · Q69

Consider the following:

  1. 1.Bacteria
  2. 2.Fungi
  3. 3.Virus

Which of the above can be cultured in artificial/synthetic medium?

  1. (a)1 and 2 only
  2. (b)2 and 3 only
  3. (c)1 and 3 only
  4. (d)1, 2 and 3
Show answer

UPSC's answer: (a)

NCERT answers it: Class 8 Curiosity, Ch 2 (The Invisible Living World: Beyond Our Naked Eye); Class 12 Biology, Ch 8 (Microbes in Human Welfare).

Class 12 Biology, ch 8 shows colonies of bacteria and of fungi growing in petri dishes. Class 8 Curiosity, ch 2: viruses multiply only after they enter a living cell, so they can't grow on an artificial medium. Answer (a).

Hindi version: UPSC's official question paper (2021), question 69 ↗

Prelims 2022 · Q38

Consider the following statements in respect of probiotics:

  1. 1.Probiotics are made of both bacteria and yeast.
  2. 2.The organisms in probiotics are found in foods we ingest but they do not naturally occur in our gut.
  3. 3.Probiotics help in the digestion of milk sugars.

Which of the statements given above is/are correct?

  1. (a)1 only
  2. (b)2 only
  3. (c)1 and 3
  4. (d)2 and 3
Show answer

UPSC's answer: (c)

NCERT answers it: Class 12 Biology, Ch 8 (Microbes in Human Welfare).

The one fact NCERT doesn't give: Probiotic bacteria help break down lactose, the sugar in milk.

Class 12 Biology, ch 8: lactic acid bacteria live in our stomach and check disease-causing microbes, so 2 is false. Both remaining options have 1; with the fact, 3 is true. Answer (c).

Beyond NCERT: probiotics include bacteria such as Lactobacillus and Bifidobacterium and yeasts such as Saccharomyces boulardii, so statement 1 is true as well. Source: NIH NCCIH, 'Probiotics: What You Need To Know' (nccih.nih.gov)

Hindi version: UPSC's official question paper (2022), question 38 ↗

Prelims 2023 · Q18

Consider the following statements:

  1. 1.Some microorganisms can grow in environments with temperature above the boiling point of water.
  2. 2.Some microorganisms can grow in environments with temperature below the freezing point of water.
  3. 3.Some microorganisms can grow in highly acidic environment with a pH below 3.

How many of the above statements are correct?

  1. (a)Only one
  2. (b)Only two
  3. (c)All three
  4. (d)None
Show answer

UPSC's answer: (c)

NCERT answers it: Class 12 Biology, Ch 8 (Microbes in Human Welfare).

The one fact NCERT doesn't give: Some microbes grow even above 100 °C: in the laboratory, a methanogen (Methanopyrus kandleri strain 116) multiplied at up to 122 °C under high pressure.

Class 12 Biology, ch 8: microbes live deep inside geysers (thermal vents) where it may be as hot as 100 °C, under snow several metres thick (2), and in highly acidic places (3). NCERT stops at 100 °C, the boiling point; with the fact, statement 1 is true too. Answer (c).

Hindi version: UPSC's official question paper (2023), question 18 ↗

Ch 9 · Biotechnology: Principles and Processes

Prelims 2019 · Q93

With reference to the recent developments in science, which one of the following statements is not correct?

  1. (a)Functional chromosomes can be created by joining segments of DNA taken from cells of different species.
  2. (b)Pieces of artificial functional DNA can be created in laboratories.
  3. (c)A piece of DNA taken out from an animal cell can be made to replicate outside a living cell in a laboratory.
  4. (d)Cells taken out from plants and animals can be made to undergo cell division in laboratory petri dishes.
Show answer

UPSC's answer: (a)

NCERT answers it: Class 12 Biology, Ch 9 (Biotechnology: Principles and Processes); Class 12 Biology, Ch 10 (Biotechnology and its Applications).

How to solve it with NCERT: Class 12 Biology, ch 9–10: NCERT shows artificial recombinant DNA made in labs (b), DNA copied outside cells by PCR (c), and cells grown in culture (d). Since those three are true, the incorrect statement must be (a). Answer (a).

Hindi version: UPSC's official question paper (2019), question 93 ↗

Ch 10 · Biotechnology and its Applications

Prelims 2019 · Q96

'RNA interference (RNAi)' technology has gained popularity in the last few years. Why?

  1. 1.It is used in developing gene silencing therapies.
  2. 2.It can be used in developing therapies for the treatment of cancer.
  3. 3.It can be used to develop hormone replacement therapies.
  4. 4.It can be used to produce crop plants that are resistant to viral pathogens.

Select the correct answer using the code given below.

  1. (a)1, 2 and 4
  2. (b)2 and 3
  3. (c)1 and 3
  4. (d)1 and 4 only
Show answer

UPSC's answer: (a)

NCERT answers it: Class 12 Biology, Ch 10 (Biotechnology and its Applications).

The one fact NCERT doesn't give: RNA interference is also being used to develop therapies for cancer.

Class 12 Biology, ch 10: RNAi silences a specific mRNA (1), and cells use it to defend against viruses, so it can make crops resist viral pathogens (4). With the fact, 2 is true too. Only option (a) has 1, 2 and 4. Answer (a).

Beyond NCERT: RNAi medicines have reached patients: the RNAi drug patisiran received its first approval in 2018. Source: PMC8007863 (Front. Pharmacol. 2021), citing Hoy S.M. (2018), 'Patisiran: first global approval', Drugs 78

Hindi version: UPSC's official question paper (2019), question 96 ↗

Prelims 2021 · Q67

Bollgard I and Bollgard II technologies are mentioned in the context of

  1. (a)clonal propagation of crop plants
  2. (b)developing genetically modified crop plants
  3. (c)production of plant growth substances
  4. (d)production of biofertilizers
Show answer

UPSC's answer: (b)

NCERT answers it: Class 12 Biology, Ch 10 (Biotechnology and its Applications).

The one fact NCERT doesn't give: Bollgard I and Bollgard II are brand names of Bt cotton technology.

Class 12 Biology, ch 10: Bt cotton is a genetically modified crop. With the fact, Bollgard is about developing GM crop plants. Answer (b).

Beyond NCERT: Bollgard II, the second generation of Bt cotton, carries two Bt toxins (Cry1Ac and Cry2Ab) to slow bollworm resistance. It was commercialised in India in 2006. Source: ICAR journal (epubs.icar.org.in, J. Res. ANGRAU 2024, doi 10.58537/jorangrau.2024.52.4.03)

Hindi version: UPSC's official question paper (2021), question 67 ↗

Prelims 2026 · Q41

Which of the following statements with regard to genetic medicine is/are correct?

  1. 1.Genetic medicines correct/compensate for the faulty genes responsible for disease.
  2. 2.Engineered viruses and lipid nanoparticles are used as carriers of the genetic medicine.
  3. 3.Genetic medicines alter the entire DNA sequence.

Select the answer using the code given below:

  1. (a)1 only
  2. (b)2 and 3 only
  3. (c)1 and 2 only
  4. (d)1, 2 and 3
Show answer

UPSC's provisional answer: (c)

NCERT answers it: Class 12 Biology, Ch 10 (Biotechnology and its Applications).

How to solve it with NCERT: Class 12 Biology, ch 10: gene therapy delivers a normal gene to compensate for a faulty one (1), for example using a retroviral vector (2). It replaces a defective gene, not the entire DNA (3 false). Answer (c).

Beyond NCERT: lipid nanoparticles are the other carrier in statement 2: mRNA vaccines wrap their mRNA in tiny lipid (fat) bubbles. Source: NHGRI (NIH), 'Understanding COVID-19 mRNA Vaccines' (genome.gov)

Hindi version: UPSC's official question paper (2026), question 41 ↗

Ch 11 · Organisms and Populations

Prelims 2021 · Q22

Consider the following kinds of organisms:

  1. 1.Copepods
  2. 2.Cyanobacteria
  3. 3.Diatoms
  4. 4.Foraminifera

Which of the above are primary producers in the food chains of oceans?

  1. (a)1 and 2
  2. (b)2 and 3
  3. (c)3 and 4
  4. (d)1 and 4
Show answer

UPSC's answer: (b)

NCERT answers it: Class 12 Biology, Ch 11 (Organisms and Populations); Class 8 Curiosity, Ch 2 (The Invisible Living World: Beyond Our Naked Eye).

How to solve it with NCERT: Class 12 Biology, ch 11: cyanobacteria photosynthesise, and copepods live as parasites on fish, so they are consumers. Class 8 Curiosity, ch 2: diatoms are microalgae that make their own food using sunlight. So 2 and 3 are producers. Answer (b).

Hindi version: UPSC's official question paper (2021), question 22 ↗

Prelims 2024 · Q28

Which one of the following shows a unique relationship with an insect that has coevolved with it and that is the only insect that can pollinate this tree?

  1. (a)Fig
  2. (b)Mahua
  3. (c)Sandalwood
  4. (d)Silk cotton
Show answer

UPSC's answer: (a)

NCERT answers it: Class 12 Biology, Ch 11 (Organisms and Populations).

Class 12 Biology, ch 11: many fig species have a one-to-one relationship with a wasp species — a fig can be pollinated only by its 'partner' wasp. The wasp, in turn, lays its eggs in the fig fruit. Answer (a).

Hindi version: UPSC's official question paper (2024), question 28 ↗

Prelims 2024 · Q29

Consider the following:

  1. 1.Butterflies
  2. 2.Fish
  3. 3.Frogs

How many of the above have poisonous species among them?

  1. (a)Only one
  2. (b)Only two
  3. (c)All three
  4. (d)None
Show answer

UPSC's answer: (c)

NCERT answers it: Class 12 Biology, Ch 11 (Organisms and Populations).

The one fact NCERT doesn't give: Some fish, such as pufferfish, are poisonous.

Class 12 Biology, ch 11: some frogs are poisonous, and the Monarch butterfly carries a chemical from a poisonous weed that makes it distasteful to birds. With the fact, all three. Answer (c).

Beyond NCERT: pufferfish carry tetrodotoxin, mainly in the liver and sex organs, and tetrodotoxin poisoning can be fatal. Source: CDC NIOSH, Tetrodotoxin: Biotoxin (emergency response card, cdc.gov)

Hindi version: UPSC's official question paper (2024), question 29 ↗

Ch 12 · Ecosystem

Prelims 2021 · Q27

In case of which one of the following biogeochemical cycles, the weathering of rocks is the main source of release of nutrient to enter the cycle?

  1. (a)Carbon cycle
  2. (b)Nitrogen cycle
  3. (c)Phosphorus cycle
  4. (d)Sulphur cycle
Show answer

UPSC's answer: (c)

NCERT answers it: Class 12 Biology, Ch 12 (Ecosystem); Class 9 Exploration, Ch 13 (Earth as a System: Energy, Matter, and Life).

The one fact NCERT doesn't give: Phosphorus has no stable gaseous form in the air, unlike carbon, nitrogen and sulphur, so it enters the cycle mainly from rocks as they weather.

Class 12 Biology, ch 12: the carbon cycle's reservoir is the air or water, but the phosphorus cycle's reservoir is the Earth's crust. Class 9 Exploration, ch 13: nitrogen's largest reservoir is the air. Class 10 Contemporary India II, ch 6: sulphur dioxide is one of the gases in polluted air. With the fact, only phosphorus has to come from rocks. Answer (c).

Hindi version: UPSC's official question paper (2021), question 27 ↗

Ch 13 · Biodiversity and Conservation

Prelims 2018 · Q60

The term "sixth mass extinction/sixth extinction" is often mentioned in the news in the context of the discussion of

  1. (a)Widespread monoculture practices in agriculture and large-scale commercial farming with indiscriminate use of chemicals in many parts of the world that may result in the loss of good native ecosystems.
  2. (b)Fears of a possible collision of a meteorite with the Earth in the near future in the manner it happened 65 million years ago that caused the mass extinction of many species including those of dinosaurs.
  3. (c)Large scale cultivation of genetically modified crops in many parts of the world and promoting their cultivation in other parts of the world which may cause the disappearance of good native crop plants and the loss of food biodiversity.
  4. (d)Mankind's over-exploitation/misuse of natural resources, fragmentation/loss of natural habitats, destruction of ecosystems, pollution and global climate change.
Show answer

UPSC's answer: (d)

NCERT answers it: Class 12 Biology, Ch 13 (Biodiversity and Conservation).

Class 12 Biology, ch 13: the 'Sixth Extinction' now in progress differs from earlier ones in its rate. Species are vanishing 100 to 1,000 times faster than in pre-human times, and our activities are responsible. Answer (d).

Hindi version: UPSC's official question paper (2018), question 60 ↗

Prelims 2018 · Q86

Why is a plant called Prosopis juliflora often mentioned in news?

  1. (a)Its extract is widely used in cosmetics.
  2. (b)It tends to reduce the biodiversity in the area in which it grows.
  3. (c)Its extract is used in the synthesis of pesticides.
  4. (d)None of the above
Show answer

UPSC's answer: (b)

NCERT answers it: Class 11 Understanding Society, Ch 3 (Environment and Society); Class 12 Biology, Ch 13 (Biodiversity and Conservation).

How to solve it with NCERT: Class 11 Understanding Society, ch 3: Prosopis juliflora (vilayati kikar) came from South America and has spread all over north India. Class 12 Biology, ch 13: such alien species can turn invasive and push out native species. Answer (b).

Hindi version: UPSC's official question paper (2018), question 86 ↗

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