Chapter 17 — Immunity, disease and biotechnology

Name the cause before the route

An infectious disease is caused by a transmissible agent such as a bacterium, virus, fungus or parasite. The agent is the pathogen; a vector is an organism that carries or transmits a pathogen between hosts in a particular disease cycle. Malaria is caused by Plasmodium parasites and transmitted through bites of infected female Anopheles mosquitoes in the standard human transmission route. The mosquito is the vector, not the parasite itself. Dengue is caused by a virus and commonly transmitted by Aedes mosquitoes. Both involve mosquitoes, but their pathogens differ. An MCQ that asks “which mosquito causes malaria?” may be colloquial; scientifically the mosquito transmits it.

Transmission routes vary. Respiratory infections can spread through particles released into air; some infections spread through contaminated water or food; others spread through vectors, blood or close contact. The route for one named disease should not be copied to another merely because both cause fever. A pathogen may also be present without the same symptoms in every person. Exposure, infection and disease are distinct states. At the exam level, match a well-established pathogen or vector with its disease, but do not infer an individual diagnosis from a symptom list.

Communicable and non-communicable are useful broad categories. An infection is communicable if its agent can pass between hosts through an applicable route. Diabetes is generally discussed as a non-communicable condition; malaria is infectious and vector-borne. “Non-communicable” does not mean a condition has no environmental or genetic causes, and “infectious” does not mean it spreads by ordinary touch. The full route matters. A good option identifies both cause and pathway without adding an unsupported universal claim.

Layers of immune defence

Skin and mucous surfaces form initial physical and chemical barriers. If a pathogen enters, innate immune responses can act quickly through cells and signalling that recognise broad patterns. Adaptive responses involve more specific recognition and memory, including B-cell and T-cell functions. Antibodies are proteins made by certain immune cells that can bind particular antigens. They are important, but immunity is not only antibodies. A multiple-choice claim that all protection is “one antibody in the blood” leaves out barriers, cells and other responses.

An antigen is a molecular feature that the immune system can recognise. It is not necessarily an entire live pathogen. Vaccines present an antigen or instructions that lead the body to make a relevant antigen, helping the immune system develop a protective response before a later exposure. Vaccine types differ, so do not state that every vaccine contains a live weakened organism. A vaccine can reduce risk or severity for the disease and population in question; it does not guarantee that no vaccinated person can ever become infected. Duration and degree of protection depend on product, pathogen and person.

Immune memory means later exposure to a familiar antigen may trigger a faster or more effective response. A booster dose can reinforce protection in a programme where recommended. This is a biological explanation, not a schedule; immunisation schedules change and vary by age, condition and policy. For an exam question asking “why vaccinate before exposure?” the answer is the development of protective immune recognition without having to experience the disease's full risk. Avoid the false assertion that vaccination is the same as taking an antibiotic after symptoms start.

Antibiotics target bacterial processes. They are not generally effective against a virus simply because the infection produces fever. Antivirals, antifungals and antiparasitic medicines are different categories. A clinician may have reasons to treat a bacterial complication in a patient with a viral infection, but that does not make an antibiotic an antiviral drug. Misuse and overuse of antimicrobials can contribute to resistance: pathogens change so medicines may become less effective. The book does not specify drugs, doses or personal treatment choices.

Outbreak language and evidence

Incidence counts new cases during a stated period in a defined population; prevalence refers to existing cases in a population at a specified time or period. They answer different questions. A disease can have a high incidence but a low point prevalence if it is brief, or low incidence with higher prevalence if it is long-lasting. A raw case count without population size and time window is not a rate. When an MCQ quotes numbers, identify denominator and period before comparing two districts or years.

An outbreak is an observed increase beyond what is expected in a particular place and time, subject to surveillance definition. A positive laboratory test may support infection, but its interpretation depends on test type, sampling and clinical context. No single test is perfectly sensitive and specific in all settings. A screening result is not automatically a final diagnosis. For exam purposes, learn what a test detects: an antigen test detects a selected antigen; an antibody test detects host antibodies; a nucleic-acid test detects selected genetic material. The exact performance and interpretation are outside a static general-science book.

Vector control aims to reduce contact between people and transmitting vectors or reduce vector populations through appropriate public-health measures. Because malaria and dengue use different mosquito genera in the standard comparisons, their details should not be swapped. Yet “mosquito control” alone does not identify a disease, and a bite from any mosquito does not necessarily transmit a pathogen. Disease risk depends on whether the insect carries an infectious agent and on the transmission setting. An exam question should identify the vector–pathogen–disease chain.

Biotechnology as use of living systems

Biotechnology is the use of biological systems, organisms or their components to make or modify products and processes. Traditional fermentation and modern DNA-based methods both fall under broad definitions, though they differ greatly in technique. Yeast fermentation can produce carbon dioxide in bread dough and ethanol in other contexts. The same organism can be used for different purposes depending on material and conditions. Not all biotechnology involves changing a genome.

DNA is a sequence of nucleotides. Polymerase chain reaction, PCR, amplifies a selected DNA segment so that more copies are available for analysis. It does not copy an entire person, create life or necessarily determine whether a pathogen is currently causing disease. Primers select a target sequence; cycles of synthesis increase the number of copies. Some tests involving RNA first convert it to DNA before amplification; the general term PCR should not be stretched to mean every molecular test is identical. An MCQ asking PCR's main role is answered by amplification of a selected nucleic-acid target.

DNA profiling compares selected genetic markers between samples. It can provide strong evidence about whether samples may share a source, subject to laboratory quality, contamination control, population statistics and chain of custody. A match alone does not prove when or how a sample was deposited, or that the matching person committed an offence. This distinction matters for an AP Police readership. Evidence interpretation is broader than a technology name. The appropriate exam-level fact is that a DNA profile can help identify or exclude possible contributors with statistical interpretation, not that it is an infallible “name tag.”

Genetic engineering deliberately changes genetic material using a range of methods. A genetically modified organism has a change introduced through a defined technological process, while conventional selective breeding changes trait frequencies by choosing parents over generations. The two may pursue similar outcomes but use different methods. No single label establishes safety, yield or environmental effect. Those require assessment of the specific organism, trait and use. Static exam notes should focus on mechanism and terminology rather than unverified current claims about a particular product.

Worked chain and test route

An item gives “female Anopheles, Plasmodium, malaria.” Classify each in order: vector, parasite pathogen, disease. If a distractor says the mosquito is a virus, it confuses biological category. If another says malaria is caused by the parasite but transmitted by contaminated drinking water, it changes the normal route. Use three separate columns—cause, carrier, illness—to avoid accepting a partly correct statement.

Another item gives a sample with very little target DNA and asks which laboratory technique makes many copies of the selected region for analysis. PCR is the expected answer. DNA profiling may later compare markers, but it is not identical to the amplification step. If a multiple-choice statement says “a DNA match proves guilt,” reject it because the scientific result addresses the sample's possible source, while guilt involves context and other evidence. This is a reasoning distinction rather than a memory trick.

Build a disease association from three separate facts

A disease name, a causative agent and a transmission route belong in separate mental columns. Tuberculosis is associated with bacteria of the Mycobacterium tuberculosis complex and commonly spreads through air from a person with infectious pulmonary disease. Cholera is associated with particular Vibrio cholerae bacteria and transmission through contaminated food or water. Malaria involves Plasmodium parasites and a mosquito vector. These comparisons show that neither fever nor a local outbreak tells you the biological category of the agent. The named cause is needed before classifying an illness as bacterial, viral or parasitic.

For introductory recall, measles and polio are viral diseases, while typhoid is bacterial. Ringworm is a fungal infection despite its common name; the word worm does not identify its cause. Ascariasis, by contrast, involves a parasitic roundworm. The list is useful when questions offer mixed pairs, but disease names do not replace evidence about an individual patient. A candidate should answer a pathogen-matching question from the established association and avoid drawing a diagnosis from one symptom such as rash, cough or fever.

A reservoir is a habitat in which an infectious agent normally persists or multiplies; a vector carries an agent between hosts in the relevant cycle. These roles can overlap in complex systems but are not interchangeable definitions. A contaminated object can be a vehicle for transfer without being a living vector. A mosquito that is not infected does not transmit malaria merely by belonging to the relevant genus. Distinguish the vector's biological identity from its infection status and the pathogen's ability to complete the transmission route.

Active and passive immunity

Active immunity develops through the person's own immune response after infection or vaccination. It generally requires time to develop and can involve immune memory. Passive immunity results from receiving antibodies produced elsewhere, such as certain maternal antibodies passed to an infant or antibodies supplied in a medical preparation. Passive protection can act without the recipient first making those antibodies, but it is usually temporary and does not create the same immune-memory process merely by supplying antibodies. The distinction is the source of the immediate protective antibodies, not whether protection is natural or manufactured.

The terms natural and artificial can be combined with active and passive in school classifications. Recovery-associated immune response is an example of naturally acquired active immunity; vaccination is artificially acquired active immunity. Maternal antibody transfer is naturally acquired passive immunity; administration of an antibody preparation is artificially acquired passive immunity. These labels do not rank the methods as better or worse in every setting. A question may mention an injection but still require passive immunity if the injected material is preformed antibody rather than an antigen intended to stimulate a new response.

B lymphocytes can develop into antibody-secreting plasma cells and memory cells. T lymphocytes have several roles, including coordination of immune responses and destruction of certain infected cells. Phagocytic cells can engulf material as part of defence. Inflammation brings changes such as increased local blood flow and immune activity, but it is not identical to infection: tissue injury and other processes can also trigger inflammation. Allergy involves an inappropriate or excessive response to a substance in a susceptible person; autoimmunity involves responses directed against the body's own components. These are different categories of immune behaviour.

Resistance is a property of microbes, not personal stubbornness

Antimicrobial resistance means microorganisms are no longer adequately affected by a medicine that previously acted against them under the relevant conditions. The person does not become an “antibiotic-resistant human” in the genetic sense intended by the term. Resistant variants can survive selection that removes more susceptible organisms, and resistance traits can spread through populations. In bacteria, genes may also move between cells by mechanisms that differ from ordinary parent-to-offspring inheritance. Selection explains why using an antimicrobial creates pressure favouring organisms able to survive it.

Antibiotic resistance is one part of the broader antimicrobial-resistance category. Antivirals, antifungals and antiparasitic agents also have resistance issues. The idea that bacteria deliberately choose to become resistant because they recognise a brand name is not a biological explanation. Variation and selection are sufficient to explain many changes, with different mechanisms in different organisms. For an exam question, separate an antibiotic's target from the microbe's mechanism of resistance. The public-health response involves appropriate prescribing, infection prevention, surveillance and other measures; an exam guide should not supply an individual medication plan.

Incidence, prevalence and attack proportion: calculate the denominator

Suppose a closed teaching population contains 2,000 people free of a specified disease at the start of a month, and 40 develop it during that month. The cumulative incidence over the month is 40/2,000 = 0.02, or 2%, under the simplified follow-up assumptions. It is also 20 new cases per 1,000 people at risk over that period. If the question instead supplies person-time, an incidence rate uses that person-time denominator. A count per population over a fixed period and a rate per person-year are related but not identical measures.

For point prevalence, suppose 60 of 2,000 residents have the condition on a specified date. Point prevalence is 60/2,000 = 3%. The 60 may include people whose illness began earlier, so this is not a count of new cases during the month. A long-lasting condition can accumulate existing cases even when the number of new cases is modest. Comparing two towns requires attention to population size, age structure, case definition, reporting and time. A larger raw case count does not automatically mean a larger individual risk.

An outbreak investigation may describe 30 illnesses among 120 people who attended a meal. The attack proportion in that group is 30/120 = 25%. If another group has 10 illnesses among 100 people, its proportion is 10%. The ratio is 25/10 = 2.5, but this association alone does not identify a specific contaminated dish or establish causation. Differences in food exposure, case definition and other factors need investigation. In a numerical MCQ, calculate the requested ratio; in an interpretation MCQ, avoid adding conclusions that the data do not support.

Screening tests: a positive result has a denominator too

Sensitivity is the proportion of people with the target condition who test positive under the evaluation conditions. Specificity is the proportion without it who test negative. These are different from the proportion of positive results that truly represent the condition, which is positive predictive value. A test can have high sensitivity and specificity yet have a substantial fraction of false positives when applied in a population where the condition is rare. This is a mathematical effect of the population and test performance, not proof that all screening is useless.

Consider a completely fictional screening exercise involving 1,000 people, of whom 100 have the target condition according to the reference method. With 90% sensitivity, 90 test positive and 10 test negative among those 100. Among the remaining 900 without the condition, 90% specificity means 810 test negative and 90 test positive. There are 180 positive results altogether, but only 90 are true positives. Positive predictive value is 90/180 = 50%. This example shows why “90% sensitive” cannot be read as “every positive has a 90% probability of being correct.”

The same exercise gives 820 negative results: 810 true negatives and 10 false negatives. Negative predictive value is 810/820, approximately 98.8%. These values belong only to the fictional population and assumptions supplied. Real evaluation depends on the test, specimen, timing, reference standard and setting. A test question can examine the arithmetic without implying that a named real-world diagnostic test has these figures. Keep synthetic data explicitly separate from current performance claims.

PCR, profiling and contamination control

In a simplified ideal PCR model, a target doubles during each fully efficient cycle. Starting with one target copy, ten ideal cycles would yield 2 to the power 10, or 1,024 copies. Starting with five copies gives 5 × 1,024 = 5,120 copies. Real reactions have efficiency limits and eventually cease to follow ideal doubling, so the calculation is a teaching model rather than a promise of laboratory yield. PCR amplifies selected sequences; it does not automatically reveal the identity, behaviour or guilt of the person associated with a specimen.

A positive control checks whether a process can produce an expected positive result with appropriate known material. A negative control helps detect contamination or other causes of an unexpected signal when the target should be absent. A positive result in a negative control raises a problem with interpreting that run; it should not be celebrated as additional evidence from the case sample. Replication, documentation and suitable controls are part of reliable measurement. These concepts are relevant beyond DNA, including chemical and microbiological tests.

DNA evidence requires a distinction between a source proposition and an activity proposition. A profile may support a proposition about who contributed biological material. It does not by itself establish how, when or during which activity that material arrived. Transfer, persistence, mixtures and contamination can complicate interpretation. A random-match probability is also not the probability that a suspect is innocent: those are different conditional questions. For police-exam science, know the role of markers and the need for statistical interpretation while avoiding claims that one numerical match replaces investigation.

Biotechnology products: mechanism before slogan

Fermentation uses biological activity to transform materials. In bread production, carbon dioxide from yeast contributes to dough expansion; in other processes, different organisms and conditions produce acids, enzymes or other products. A microorganism used in an industrial process is not automatically a pathogen. Conversely, calling a process natural does not establish that every product or preparation is safe. The organism, strain, process controls and intended use all matter. Biotechnology is broader than genetic engineering and includes methods that long predate modern molecular genetics.

In a standard recombinant-DNA description, a selected DNA sequence is joined to other DNA and introduced into a suitable host system for a defined purpose. A vector in this context can be a DNA carrier such as a plasmid, which differs from a disease vector such as a mosquito. The word has a different technical meaning in each setting. Restriction enzymes can cut DNA at characteristic sequences, while DNA ligase joins DNA strands at suitable ends. Do not swap the cutting and joining functions merely because both enzymes appear in one workflow.

Retrieval practice with reasons

Exercise A: Forty existing cases among 800 residents on a particular date give 5% point prevalence. Exercise B: In a stated perfect-doubling model, three starting target copies after eight PCR cycles give 3 × 256 = 768 copies. Exercise C: Receiving preformed antibodies is passive immunity; generating an immune response to vaccine antigen is active immunity. Exercise D: Ringworm is fungal despite its name, while malaria is parasitic rather than bacterial.

Exercise E: A profile comparison supports a possible common biological source. It does not independently prove the activity during which material was deposited. Exercise F: A positive signal appears in a control that should contain no target. Investigate the control failure before treating the case result as reliable. Exercise G: A test detects host antibodies. It is measuring part of the host response, not directly counting whole pathogens. Explain the distinction before choosing among antigen, antibody and nucleic-acid testing options.

Recall and review

Differentiate pathogen, vector and disease using malaria and dengue. Describe barrier, innate and adaptive defence in broad sequence. Explain why vaccination and antibiotic treatment serve different purposes. Identify why antibiotics generally do not treat viruses and why misuse can support resistance. Compare antigen, antibody and nucleic-acid tests by what they detect. Finally, state what PCR amplifies and what a DNA-profile match can and cannot establish. Attempt the chapter practice set, then use the explanations to revisit any uncertain concepts.

Figure 17. Original chapter diagram.

Practice 31 questions

Choose one answer for each item. The answer key and explanations follow this chapter set.

1. Who discovered penicillin, the first antibiotic, in 1928?

A. Alexander Fleming B. Selman Waksman C. Edward Jenner D. Louis Pasteur

2. Which human disease was declared eradicated worldwide by the World Health Organization in 1980?

A. Poliomyelitis B. Smallpox C. Measles D. Tuberculosis

3. Arrange the following landmarks in chronological order:
P. Discovery of penicillin by Alexander Fleming
Q. Edward Jenner's smallpox vaccine
R. Birth of Dolly, the cloned sheep
S. Louis Pasteur's rabies vaccine

A. Q, S, P, R B. Q, S, R, P C. Q, P, S, R D. S, Q, P, R

4. Arrange these public-health and microbiology milestones from earliest to latest: A Fleming reports penicillin; B Koch identifies the tuberculosis bacterium; C Jenner demonstrates smallpox vaccination; D Pasteur gives a rabies vaccine.

A. C, D, B, A B. B, C, D, A C. C, B, D, A D. C, B, A, D

5. A vaccine produces immune memory because it primarily stimulates the recipient to make:

A. Only ready-made antibodies imported from another person B. Its own adaptive immune response and memory cells C. Urea and digestive enzymes D. Red blood cells against the pathogen

6. Bt cotton, grown widely in India, has been genetically modified mainly to resist which pest?

A. Bollworm B. Whitefly C. Aphid D. Locust

7. Dolly the sheep was cloned by transferring the nucleus of which type of cell from an adult sheep into an enucleated egg?

A. Embryonic stem cell B. Mammary gland (udder) cell C. Red blood cell D. Sperm cell

8. Golden Rice, a genetically engineered variety of rice, was developed mainly to combat the deficiency of:

A. Vitamin A B. Vitamin C C. Vitamin D D. Vitamin B12

9. Which GM crop was placed under a central-government moratorium on commercial release in India in February 2010?

A. Flavr Savr tomato B. Bt brinjal C. Bt cotton D. Golden rice

10. Consider the following statements:
Statement I: Antibiotics are not effective against viral infections such as the common cold.
Statement II: Smallpox was declared eradicated worldwide by the WHO in 1980.
Which of the above is/are correct?

A. Only I B. Only II C. Both I and II D. Neither I nor II

11. Which of the following pairs of scientist and discovery is NOT correctly matched?

A. Karl Landsteiner — ABO blood groups B. Edward Jenner — Smallpox vaccine C. Robert Koch — Tuberculosis bacterium D. Alexander Fleming — Streptomycin

12. The central Indian law that provides for regulation of human organ transplantation and recognises brain-stem death was originally enacted in which year?

A. 1988 B. 1994 C. 2002 D. 2011

13. Fleming shared the 1945 Nobel Prize in Physiology or Medicine for penicillin with which two researchers who advanced its therapeutic development?

A. James Watson and Francis Crick B. Frederick Banting and John Macleod C. Howard Florey and Ernst Chain D. Jonas Salk and Albert Sabin

14. Norman Borlaug, called the 'Father of the Green Revolution', developed high-yielding dwarf varieties of which crop in Mexico?

A. Rice B. Cotton C. Wheat D. Maize

15. Robert Edwards was awarded the 2010 Nobel Prize in Physiology or Medicine for the development of:

A. Mammalian cloning B. Oral polio vaccine C. Recombinant human insulin D. In vitro fertilisation (IVF)

16. Who is regarded as the "Father of the Green Revolution in India"?

A. M.S. Swaminathan B. Norman Borlaug C. Verghese Kurien D. Har Gobind Khorana

17. Which Indian committee under the Environment Ministry appraises proposals for environmental release of genetically engineered organisms, including crops?

A. Genetic Engineering Appraisal Committee (GEAC) B. Council of Scientific and Industrial Research (CSIR) C. Food Safety and Standards Authority of India (FSSAI) D. Indian Council of Agricultural Research (ICAR)

18. Candidiasis, caused by Candida albicans, is an infection due to which type of organism?

A. Bacterium B. Virus C. Fungus D. Protozoan

19. Leprosy, treated with multi-drug therapy (MDT), is caused by:

A. Mycobacterium leprae B. Mycobacterium tuberculosis C. Clostridium tetani D. Treponema pallidum

20. Match List-I (Body component) with List-II (Role):
List-I: (a) B-lymphocytes (b) T-lymphocytes (c) Interferons (d) Platelets
List-II: (i) Proteins that protect neighbouring cells from viral attack (ii) Clump at a wound to start clotting (iii) Mature in the bone marrow and produce antibodies (iv) Mature in the thymus

A. a-iv, b-iii, c-i, d-ii B. a-iii, b-iv, c-ii, d-i C. a-iii, b-iv, c-i, d-ii D. a-i, b-iv, c-iii, d-ii

21. Match List-I (Disease) with List-II (Causative organism):
List-I: (a) Tetanus (b) Diphtheria (c) Giardiasis (d) Ringworm
List-II: (i) Trichophyton (ii) Giardia lamblia (iii) Clostridium tetani (iv) Corynebacterium diphtheriae

A. a-iii, b-iv, c-ii, d-i B. a-iv, b-iii, c-ii, d-i C. a-iii, b-iv, c-i, d-ii D. a-iii, b-ii, c-iv, d-i

22. Match List-I (Disease) with List-II (Type of causative organism):
List-I: (a) Ringworm (b) Rabies (c) Sleeping sickness (d) Diphtheria
List-II: (i) Bacterium (ii) Fungus (iii) Protozoan (iv) Virus

A. a-i, b-ii, c-iii, d-iv B. a-ii, b-iii, c-iv, d-i C. a-iv, b-ii, c-i, d-iii D. a-ii, b-iv, c-iii, d-i

23. A person receives an antiserum containing ready-made antibodies after a suspected exposure. This protection is classified as:

A. Natural active immunity B. Artificial passive immunity C. Natural passive immunity D. Autoimmunity

24. Why does pasteurisation of milk reduce infection risk?

A. It sterilises milk by removing all microorganisms and spores B. Controlled heating reduces many harmful microbes without making the milk sterile C. It converts milk protein into an antibiotic D. It adds antibodies to milk

25. A newborn baby receiving antibodies from its mother through colostrum, the first breast milk, is an example of which type of immunity?

A. Passive immunity B. Active immunity C. Autoimmunity D. Allergic hypersensitivity

26. A person infected with HIV is at increased risk of opportunistic infection mainly because the virus targets which immune cell population?

A. CD4-positive T lymphocytes B. Red blood cells C. Platelets only D. Neutrophils only

27. Typhoid, a disease spread through contaminated food and water, is caused by which bacterium?

A. Vibrio cholerae B. Salmonella typhi C. Mycobacterium tuberculosis D. Clostridium tetani

28. Which enzyme present in tears and saliva destroys the cell walls of bacteria?

A. Lysozyme B. Pepsin C. Trypsin D. Salivary amylase

29. Which feature makes interferons part of early antiviral defence?

A. They are antibodies that bind only one named viral strain B. They are signalling proteins that can induce an antiviral state in nearby cells C. They directly form the clot at a wound D. They are enzymes that digest food proteins

30. Which chemical, released by the body during an allergic reaction, causes sneezing, itching and swelling and is blocked by antihistamine medicines?

A. Histamine B. Insulin C. Interferon D. Lysozyme

31. Consider the following statements:
Statement I: The Aedes aegypti mosquito, which spreads dengue, typically bites during the daytime.
Statement II: Antibiotics are effective in curing viral infections such as influenza.
Which of the above is/are correct?

A. Only I B. Only II C. Both I and II D. Neither I nor II

Answers and explanations

1. A. Alexander Fleming observed the antibacterial effect of a Penicillium mould in 1928. Turning penicillin into an effective medicine required later work by many scientists, including Florey and Chain. Jenner is associated with smallpox vaccination, Pasteur with rabies vaccination, and Waksman’s laboratory with streptomycin.

2. B. Smallpox was declared eradicated worldwide by the WHO in 1980, the only human disease eradicated through vaccination so far. Polio, measles and tuberculosis still occur in the world.

3. A. Jenner's smallpox vaccine came in 1796 (Q), Pasteur's rabies vaccine in 1885 (S), Fleming's penicillin in 1928 (P) and Dolly's birth in 1996 (R). Correct order: Q, S, P, R.

4. C. Jenner’s smallpox vaccine was demonstrated in 1796, Koch identified the TB bacterium in 1882, Pasteur’s rabies vaccine followed in 1885 and Fleming reported penicillin in 1928. Thus C, B, D, A. This ordering tests the close 1882 and 1885 dates.

5. B. Vaccination presents a safe antigenic stimulus so the recipient develops an adaptive response and immunological memory. Giving preformed antibodies instead is passive immunisation and usually does not create the same long-lived memory.

6. A. Bt cotton expresses insecticidal protein derived from Bacillus thuringiensis and is designed chiefly to protect against certain bollworm larvae. Efficacy depends on the event, pest and resistance management. It does not itself provide broad protection against whiteflies or aphids.

7. B. Dolly was created by transferring the nucleus of an adult mammary-gland cell into an egg whose nucleus had been removed. Born in 1996, she was the first mammal cloned from an adult somatic cell. Nuclear DNA mainly matched the cell donor, but calling the two animals genetically identical without qualification overlooks mitochondrial DNA and developmental differences.

8. A. Golden Rice was engineered to make beta-carotene, a provitamin A carotenoid, in the edible grain. The body can convert beta-carotene to vitamin A. Its intended public-health purpose was to help address vitamin A deficiency; nutritional impact also depends on diet, conversion and delivery.

9. B. The 2010 decision concerned Bt brinjal. It is a dated policy fact; approval status should be rechecked against current government records before a later edition describes its present legal status. Bt cotton had already been approved for cultivation in India.

10. C. Both statements are correct. Antibiotics act on bacteria and do not treat the viruses that cause ordinary colds; a separate bacterial complication may sometimes need treatment. The World Health Assembly declared smallpox eradicated in 1980.

11. D. Fleming is associated with penicillin, not streptomycin. Streptomycin was isolated in Waksman’s laboratory by Albert Schatz and colleagues; assigning it solely to Waksman would obscure their contribution. Landsteiner described ABO blood groups, Jenner demonstrated smallpox vaccination and Koch identified the tuberculosis bacterium.

12. B. The Transplantation of Human Organs Act was enacted in 1994. The 2011 amendment extended the framework to tissues, and its current title is the Transplantation of Human Organs and Tissues Act, 1994. This asks the original enactment year, not the amendment year.

13. C. Fleming, Howard Florey and Ernst Chain shared the 1945 Nobel Prize for the discovery of penicillin and its curative effect. Florey and Chain led crucial experimental and clinical development; production at scale also involved other teams and industry.

14. C. Borlaug developed high-yielding, disease-resistant semidwarf wheat in Mexico. Indian scientists and institutions, prominently M. S. Swaminathan, advanced its use in India. The Green Revolution had many contributors and uneven regional outcomes, so no single researcher “turned” two states into a grain bowl alone.

15. D. Robert Edwards pioneered IVF, which led to the birth of Louise Brown, the world's first IVF baby, in England in 1978. His surgical collaborator Patrick Steptoe had died before 2010, and Nobel Prizes are not awarded posthumously.

16. A. M. S. Swaminathan is widely called the Father of the Green Revolution in India for his leadership in crop improvement and agricultural policy. Norman Borlaug is widely associated with the wider Green Revolution, while Verghese Kurien is associated with India’s dairy cooperative movement.

17. A. The Genetic Engineering Appraisal Committee (GEAC), under the Ministry of Environment, Forest and Climate Change, appraises environmental-release proposals under India’s biotechnology rules. A committee appraisal is part of a regulatory process; it should not be described as automatically authorising all cultivation or food uses.

18. C. Candida albicans is a yeast, which is a fungus, so candidiasis is fungal. Candida can also live harmlessly on the body; infection occurs when conditions allow overgrowth. A clinical diagnosis or treatment choice cannot be inferred from this classification question.

19. A. Leprosy is primarily caused by Mycobacterium leprae; another related species can also cause cases. It usually requires prolonged close contact for transmission, is treatable with multidrug therapy, and should not be associated with casual-contact stigma. The other listed bacteria cause different diseases.

20. C. B lymphocytes develop and mature in the bone marrow and can differentiate into antibody-secreting plasma cells (iii). T lymphocytes mature in the thymus (iv). Interferons participate in antiviral signalling (i), and platelets help initiate haemostasis (ii). Hence a-iii, b-iv, c-i, d-ii.

21. A. Tetanus is caused by Clostridium tetani (a-iii), diphtheria by Corynebacterium diphtheriae (b-iv), giardiasis by the protozoan Giardia lamblia (c-ii), and ringworm by fungi such as Trichophyton (d-i).

22. D. Ringworm is a fungal disease (ii), rabies is viral (iv), sleeping sickness is caused by the protozoan Trypanosoma (iii) and diphtheria by the bacterium Corynebacterium diphtheriae (i): a-ii, b-iv, c-iii, d-i.

23. B. Administered antiserum provides preformed antibodies and is artificial passive immunisation. It can act promptly, but the recipient has not produced the antibodies through a vaccine response. Natural passive immunity includes transfer of maternal antibodies.

24. B. Pasteurisation uses specified heating and cooling conditions to reduce pathogens and spoilage microbes. It does not guarantee sterility or remove all spores. The process was named for Louis Pasteur’s work on microbial spoilage.

25. A. Colostrum supplies maternal antibodies, notably secretory IgA, so the infant receives naturally acquired passive immunity. This is protection from transferred antibodies; active immunity arises when the infant’s own immune system responds to infection or vaccination.

26. A. HIV infects and depletes CD4-positive T helper cells, disrupting immune coordination and increasing risk of opportunistic infections when immune suppression becomes advanced. A diagnosis or clinical prognosis requires proper testing and medical evaluation.

27. B. Typhoid fever is caused by Salmonella enterica serovar Typhi and is usually acquired by the faecal–oral route. Blood culture is a principal diagnostic test. The Widal serology test has poor specificity and is not recommended as a stand-alone confirmation.

28. A. Lysozyme in tears and saliva cuts a component of bacterial peptidoglycan cell walls, contributing to innate defence. It does not destroy every bacterium. Amylase digests starch; pepsin and trypsin digest proteins.

29. B. Interferons are cytokine signalling proteins released in response to infection. They can induce antiviral defences in neighbouring cells and help coordinate immunity. They do not act as pathogen-specific antibodies or clotting platelets.

30. A. Histamine released during an allergic reaction to allergens such as pollen, dust or certain foods causes sneezing, itching and swelling; antihistamines block its action. Interferons protect against viruses and lysozyme attacks bacterial walls.

31. A. Only I is correct. Aedes aegypti usually bites by day and transmits dengue; biting times are tendencies, not an absolute rule for every mosquito. Antibiotics do not cure influenza, which is caused by a virus. Medicines for bacterial complications are a separate matter.