Section 15 — Board Previous Year Questions (Class 12 Biology · Chapter 7)
Chapter 7 (Human Health and Disease) is one of the most dependable scoring chapters in the Class 12 Biology Board paper. On average, 7–10 marks of every paper come from this chapter — spread across MCQs, 2/3-mark short answers, and very often a 5-mark question on the immune response, HIV/AIDS, cancer or drug and alcohol abuse.
This section curates 24 high-yield Board questions in the exact format and weighting the examiners use:
| Marks | Number of Qs | Typical paper allocation |
|---|---|---|
| 1 mark | 7 questions (Q1–Q7) | 2–3 / paper |
| 2 marks | 6 questions (Q8–Q13) | 2 / paper |
| 3 marks | 6 questions (Q14–Q19) | 1–2 / paper |
| 5 marks | 5 questions (Q20–Q24) | 1 / paper (very high probability) |
| Total | 24 questions | ~24 marks worth |
How to use: Cover the answer, attempt it yourself scaled to the marks, then check against the model answer and its keyword notes.
No quiz at the end: Pair this set with the Solved Examples and the NEET PYQ section.
What the Board Keeps Asking
Most questions on Chapter 7 fall into six recurring themes:
1. Common human diseases (1- or 2-mark) — pathogen–disease matching, vectors, symptoms, life cycle of Plasmodium.
2. Immunity (2-, 3- or 5-mark) — innate vs acquired, active vs passive, humoral vs cell-mediated, structure of the antibody, primary vs secondary response.
3. Vaccination and lymphoid organs (2- or 3-mark) — how vaccines exploit memory, primary vs secondary lymphoid organs.
4. AIDS (3- or 5-mark) — HIV as a retrovirus, transmission routes, the macrophage–helper T-cell mechanism, diagnosis (ELISA), prevention.
5. Cancer (3- or 5-mark) — contact inhibition, benign vs malignant, metastasis, carcinogens, oncogenes, detection and treatment.
6. Drugs and alcohol abuse (2-, 3- or 5-mark) — opioids, cannabinoids, coca alkaloids, source plants, addiction vs dependence, prevention.
1-Mark Questions (Q1–Q7)
Q1. [1 mark] Name the causative organism of typhoid and the test used to confirm it.
Answer: Salmonella typhi; confirmed by the Widal test.
Keyword note: both the pathogen name and Widal test are needed for the full mark.
Q2. [1 mark] Which cells does HIV finally destroy, causing immunodeficiency?
Answer: The helper T-lymphocytes ( cells).
Q3. [1 mark] Name the enzyme that allows the RNA genome of HIV to form viral DNA inside the host cell.
Answer: Reverse transcriptase.
Q4. [1 mark] What is the property called by which normal cells stop dividing on contact with other cells, and which cancer cells lose?
Answer: Contact inhibition.
Q5. [1 mark · Assertion–Reason]
Assertion (A): Colostrum provides passive immunity to a newborn. Reason (R): Colostrum is rich in IgA antibodies.
Options: (a) Both A and R true and R explains A. (b) Both true but R doesn't explain A. (c) A true, R false. (d) A false, R true.
Answer: (a) — colostrum gives ready-made antibodies (passive immunity), and it is the abundant IgA in it that does so, so R correctly explains A.
Q6. [1 mark] From which plant and its part is heroin (smack) obtained?
Answer: It is derived from morphine present in the latex of the opium poppy, Papaver somniferum.
Q7. [1 mark] Name the two primary lymphoid organs of the human body.
Answer: Bone marrow and thymus.
2-Mark Questions (Q8–Q13)
Q8. [2 marks] Distinguish between innate immunity and acquired immunity on the basis of specificity and memory.
Answer: Innate immunity is non-specific (acts against any foreign agent), is present from birth, and has no memory. Acquired immunity is pathogen-specific, develops after exposure, and shows memory, giving a faster, stronger response on re-exposure.
Keyword note: the two comparison axes — specificity and memory — carry the marks.
Q9. [2 marks] Differentiate between active immunity and passive immunity, giving one example of each.
Answer: In active immunity the host's own body makes antibodies after exposure to an antigen (a live/dead microbe or vaccine); it is slow but long-lasting, e.g. immunity after vaccination or natural infection. In passive immunity ready-made antibodies are given from outside; it is fast but short-lived, e.g. antibodies in colostrum, or antitetanus/antivenom injection.
Q10. [2 marks] Name the two types of acquired immune response and state the lymphocyte responsible for each.
Answer: (i) Humoral (antibody-mediated) immune response — carried out by B-lymphocytes, which produce antibodies in the blood. (ii) Cell-mediated immune response (CMI) — carried out by T-lymphocytes, responsible also for graft rejection.
Q11. [2 marks] How does vaccination provide immunity against a disease?
Answer: A vaccine introduces antigenic proteins or a weakened/inactivated pathogen into the body. This makes the body produce antibodies and generate memory B- and T-cells. On later exposure to the actual pathogen, these memory cells mount a rapid, massive secondary response that neutralises it.
Q12. [2 marks] Name the causative agent and the vector of malaria. Which is the most serious form?
Answer: Malaria is caused by the protozoan Plasmodium (species P. vivax, P. malariae, P. falciparum), transmitted by the bite of the female Anopheles mosquito. Malignant malaria caused by Plasmodium falciparum is the most serious and can be fatal.
Q13. [2 marks] Differentiate between addiction and dependence with respect to drug/alcohol abuse.
Answer: Addiction is a psychological attachment to the euphoria or well-being drugs/alcohol produce, driving a person to take them even when not needed. Dependence is the body's tendency to show an unpleasant withdrawal syndrome (anxiety, shakiness, nausea, sweating) if the regular dose is stopped abruptly.
3-Mark Questions (Q14–Q19)
Q14. [3 marks] Describe the life cycle of Plasmodium in brief, naming the infective stage and the role of each host.
Answer: Plasmodium enters the human body as sporozoites (the infective stage) through the bite of an infected female Anopheles mosquito. The parasites first multiply in the liver cells, then attack and multiply inside the red blood cells, rupturing them. This rupture releases a toxin, haemozoin, responsible for the recurring chill and high fever. When another female Anopheles bites the infected person, the parasite enters the mosquito, develops further, and forms sporozoites stored in its salivary glands, ready to infect the next person.
Keyword note: sporozoite (infective stage), liver → RBC, haemozoin, two hosts.
Q15. [3 marks] List the four types of barriers that make up innate immunity, with one example each.
Answer: (1) Physical barriers — skin and the mucus lining of respiratory, gastrointestinal and urogenital tracts. (2) Physiological barriers — acid in the stomach, saliva, tears. (3) Cellular barriers — PMNL-neutrophils, monocytes, natural killer cells and tissue macrophages that phagocytose microbes. (4) Cytokine barriers — interferons secreted by virus-infected cells that protect neighbouring cells.
Q16. [3 marks] How does HIV cause immunodeficiency after entering the body? Name the test used to detect the infection.
Answer: HIV enters macrophages, where its RNA is copied into viral DNA by reverse transcriptase; this DNA integrates into the host DNA and directs the cell to make more viruses, so the macrophage acts as an HIV factory. HIV also enters helper T-lymphocytes, replicates, and the progeny viruses destroy more cells. The progressive fall in helper T-cell numbers leaves the person unable to fight infections that are normally harmless. Detected by the ELISA test.
Q17. [3 marks] How is a cancerous cell different from a normal cell? Explain the term metastasis.
Answer: Normal cells show contact inhibition and their growth and differentiation are tightly regulated. Cancer cells lose contact inhibition, so they divide uncontrollably to form masses called tumors, and they compete with normal cells for nutrients. Metastasis is the property of malignant tumor cells to detach, travel through the blood to distant sites, and start new tumors there — the most feared property of malignant tumors.
Q18. [3 marks] What are carcinogens? Classify them with examples, and name two techniques used to detect internal cancers.
Answer: Carcinogens are physical, chemical or biological agents that transform normal cells into cancerous cells. Examples: physical/radiation — ionising X-rays and gamma rays, non-ionising UV; chemical — components of tobacco smoke; biological — oncogenic viruses carrying viral oncogenes. Internal cancers are detected by radiography (X-ray), CT scan and MRI, and by biopsy/histopathology.
Q19. [3 marks] Name the three main categories of commonly abused drugs, their source plants, and one effect of each.
Answer: (1) Opioids — e.g. heroin/morphine from the opium poppy, Papaver somniferum; act as depressants that slow body functions. (2) Cannabinoids — marijuana, hashish, charas, ganja from Cannabis sativa; affect the cardiovascular system and brain. (3) Coca alkaloids (cocaine) — from Erythroxylum coca; a potent CNS stimulant producing euphoria and, in excess, hallucinations.
5-Mark Questions (Q20–Q24)
Q20. [5 marks] Explain the acquired immune response of the human body. Distinguish humoral from cell-mediated immunity, describe the structure of an antibody, and explain the primary and secondary responses.
Answer:
Acquired immunity is pathogen-specific and shows memory, carried out by two lymphocytes — B-cells and T-cells.
Humoral (antibody-mediated) immunity: B-lymphocytes produce antibodies that circulate in the blood and fight pathogens. Cell-mediated immunity (CMI): T-lymphocytes act directly; they do not secrete antibodies but help B-cells, and are responsible for graft rejection and self/non-self recognition.
Structure of an antibody: each molecule has four peptide chains — two light and two heavy — and is represented as . Types include IgA, IgM, IgE and IgG.
Primary vs secondary response: the first encounter with a pathogen gives a low-intensity primary response; because of memory cells, a later encounter with the same pathogen gives a highly intensified secondary (anamnestic) response. This memory is the basis of vaccination.
Keyword note: B vs T, , Ig types, primary vs secondary/anamnestic.
Q21. [5 marks] What is AIDS? Name its causative agent and its nature. Describe how HIV spreads, how it damages the immune system, and any two preventive measures.
Answer:
AIDS — Acquired Immuno Deficiency Syndrome — is a deficiency of the immune system acquired during a person's lifetime (not congenital). It is caused by the Human Immunodeficiency Virus (HIV), a retrovirus with an RNA genome enclosed in an envelope.
Transmission: (a) sexual contact with an infected person; (b) transfusion of contaminated blood/blood products; (c) sharing infected needles; (d) from an infected mother to child through the placenta. It does not spread by touch or ordinary physical contact.
Mechanism: inside the body HIV enters macrophages, where reverse transcriptase makes viral DNA that integrates into host DNA and produces new viruses. HIV also infects and replicates in helper T-lymphocytes, whose numbers fall progressively, leaving the patient open to infections by bacteria (e.g. Mycobacterium), viruses, fungi and parasites.
Prevention (any two): making blood in blood banks safe, using only disposable needles and syringes, free distribution of condoms and advocating safe sex, controlling drug abuse, and public education through bodies such as NACO.
Q22. [5 marks] Describe cancer under the following heads: contact inhibition and tumor formation, types of tumors, causes, and methods of treatment.
Answer:
Contact inhibition and tumors: normal cells stop dividing on contact with neighbours (contact inhibition) and are tightly regulated. Cancer cells lose this control and divide continuously to form tumors.
Types of tumors: Benign tumors stay confined to one site and cause little harm. Malignant tumors are masses of rapidly dividing neoplastic cells that invade and damage surrounding tissue, starve normal cells, and show metastasis — spreading through blood to start new tumors elsewhere.
Causes: transformation is induced by carcinogens — ionising radiations (X-rays, gamma rays), non-ionising UV, chemicals in tobacco smoke, and oncogenic viruses with viral oncogenes. Normal cells also carry cellular oncogenes (proto-oncogenes) that can trigger cancer when activated.
Treatment: the three main approaches are surgery, radiotherapy (lethal irradiation of tumor cells) and chemotherapy (drugs that kill cancer cells); often used in combination. Immunotherapy with biological response modifiers such as α-interferon activates the patient's immune system against the tumor.
Q23. [5 marks] Explain the harmful effects of drug and alcohol abuse on an individual, and outline the measures for its prevention and control among adolescents.
Answer:
Harmful effects: immediate effects include reckless behaviour, vandalism and violence; excessive doses can cause coma and death from respiratory failure, heart failure or cerebral haemorrhage. Intravenous drug users risk AIDS and Hepatitis B through shared needles. Chronic use damages the nervous system and liver (cirrhosis), and abuse during pregnancy harms the foetus. Misuse of anabolic steroids in sport causes masculinisation in females, reduced sperm production in males, aggression, mood swings and, in adolescents, stunted growth.
Prevention and control (any relevant points): (i) avoid undue peer pressure — respect the child's own capacity; (ii) education and counselling to handle stress and failure, channelling energy into sports, music, yoga; (iii) seeking help from parents and peers; (iv) looking for danger signs such as falling grades, absenteeism and withdrawal; (v) seeking professional and medical help from psychologists and de-addiction/rehabilitation programmes.
Q24. [5 marks] Describe any five common infectious diseases of humans, naming the causative pathogen, mode of transmission and one key symptom for each.
Answer:
- Typhoid — bacterium Salmonella typhi; spread through contaminated food and water; key symptom: sustained high fever (39–40 °C) with weakness and stomach pain (confirmed by Widal test).
- Pneumonia — bacteria Streptococcus pneumoniae / Haemophilus influenzae; spread by inhaling droplets or sharing utensils; key symptom: fluid-filled alveoli causing difficulty in breathing, fever and chills.
- Common cold — Rhino viruses; spread by droplets and contaminated objects; key symptom: nasal congestion and discharge, sore throat, cough.
- Amoebiasis — protozoan Entamoeba histolytica; spread by faecal contamination of food/water via houseflies; key symptom: stools with excess mucus and blood, abdominal cramps.
- Ringworm — fungi Microsporum, Trichophyton, Epidermophyton; spread by soil or shared towels/clothes/combs; key symptom: dry, scaly lesions with intense itching on skin, nails, scalp.
(Ascariasis by Ascaris and filariasis by Wuchereria are equally acceptable alternatives.)
End of Section 15
You have now worked through 24 high-yield Board questions spanning common diseases, immunity, vaccination, AIDS, cancer and drug/alcohol abuse. If you can answer the five 5-markers (Q20–Q24) from memory with their key points, you have effectively secured this chapter's contribution to your paper.
Final tip: On exam day, draw and label diagrams wherever allowed — the antibody molecule (), the Plasmodium life cycle, HIV replication — examiners give marks for clear labelled structure. Tabulate comparison-type answers (innate vs acquired, active vs passive, benign vs malignant, addiction vs dependence).