Class 9 Biology Chapter 7: Human Health and Disease MCQ Quiz with Answers

The rationalized CBSE Class 9 syllabus (2024-25) has shifted assessment focus toward Multiple Choice Questions (MCQs) for several pedagogical reasons. First, MCQs test conceptual clarity rather than rote memorization—they force you to distinguish between similar concepts (e.g., active vs. passive immunity, benign vs. malignant tumours). Second, the CBSE board now allocates 20–30% of marks to objective-type questions in most subjects, including Biology. Third, MCQs develop rapid decision-making skills essential for competitive exams (JEE, NEET) taken by Class 9 students aiming ahead. For Chapter 7 specifically, MCQs effectively assess your ability to identify pathogens from symptoms, trace disease transmission pathways, and apply health concepts to real-world scenarios like vaccine schedules and drug abuse prevention. Unlike descriptive questions, MCQs eliminate ambiguity—there is one correct answer—making self-assessment reliable. A strong MCQ practice routine also reduces exam anxiety because you've encountered similar question patterns. Start a 3-day free trial at cbsetutor.ai to access AI-powered MCQ explanations tailored to your weak areas.

**Question 1.** Which of the following is an example of a bacterial pathogen? (A) Plasmodium (B) *Vibrio cholerae* (C) Influenza virus (D) Candida **Answer:** (B) *Vibrio cholerae* **Reason:** *Vibrio cholerae* is a bacterium that causes cholera; Plasmodium is a protozoan, influenza is a virus, and Candida is a fungus. --- **Question 2.** Which vaccine is administered at birth in India as per the national immunization schedule? (A) BCG and Polio (OPV/IPV) (B) MMR (C) Hepatitis B (D) DPT **Answer:** (A) BCG and Polio (OPV/IPV) and Hepatitis B **Reason:** BCG (tuberculosis), Polio, and Hepatitis B vaccines are given at birth; others are given at later ages. --- **Question 3.** AIDS is caused by which virus? (A) HIV-1 (B) Hepatitis B virus (C) Ebola virus (D) Measles virus **Answer:** (A) HIV-1 **Reason:** HIV-1 (Human Immunodeficiency Virus) attacks CD4⁺ T cells, leading to AIDS (Acquired Immunodeficiency Syndrome). --- **Question 4.** Which of the following is a non-communicable disease? (A) Malaria (B) Tuberculosis (C) Diabetes (D) Measles **Answer:** (C) Diabetes **Reason:** Diabetes is a metabolic disorder not transmitted person-to-person; others are communicable diseases. --- **Question 5.** What is the primary function of white blood cells (WBCs)? (A) Oxygen transport (B) Defense against pathogens (C) Blood clotting (D) Nutrient absorption **Answer:** (B) Defense against pathogens **Reason:** WBCs (lymphocytes, neutrophils, macrophages) form the immune system's first line of defense. --- **Question 6.** Which of the following is a symptom of tuberculosis? (A) Persistent cough lasting >3 weeks (B) Acute diarrhea (C) Skin rash (D) Severe headache **Answer:** (A) Persistent cough lasting >3 weeks **Reason:** TB primarily affects lungs; chronic cough with blood-tinged sputum is a hallmark symptom. --- **Question 7.** Alcohol abuse primarily damages which organ? (A) Heart (B) Liver (C) Brain (D) All of the above **Answer:** (D) All of the above **Reason:** Chronic alcohol consumption causes cirrhosis (liver), cardiomyopathy (heart), and cognitive impairment (brain). --- **Question 8.** Which of the following is an example of active immunity? (A) Antibodies from mother's milk (B) Vaccination (C) Serum injection (D) Blood transfusion **Answer:** (B) Vaccination **Reason:** Vaccination stimulates your own immune cells to produce antibodies; passive immunity is acquired from external sources. --- **Question 9.** Malaria is transmitted by which mosquito? (A) *Aedes aegypti* (B) *Culex* species (C) *Anopheles* species (D) *Culex quinquefasciatus* **Answer:** (C) *Anopheles* species **Reason:** Female *Anopheles* mosquitoes transmit the Plasmodium parasite; *Aedes* transmits dengue, *Culex* transmits lymphatic filariasis. --- **Question 10.** Which lifestyle factor does NOT increase cancer risk? (A) Smoking (B) Regular physical exercise (C) Excessive alcohol consumption (D) Obesity **Answer:** (B) Regular physical exercise **Reason:** Exercise reduces cancer risk; smoking, alcohol, and obesity are established risk factors.

**Question 11.** A patient exhibits fever, chills, and a rash 10 days after a mosquito bite in a malaria-endemic area. Which stage of the parasite's life cycle is most likely active in the bloodstream? (A) Sporozoite (in salivary glands) (B) Merozoite (in RBCs) (C) Gametocyte (in RBCs) (D) Oocyst (in mosquito midgut) **Answer:** (B) Merozoite (in RBCs) **Reason:** Merozoites released from the liver multiply in RBCs, causing hemolysis, fever, and the characteristic clinical symptoms. --- **Question 12.** Which of the following best describes the difference between innate and adaptive immunity? (A) Innate is present from birth; adaptive develops after exposure. (B) Innate is specific; adaptive is non-specific. (C) Innate requires vaccination; adaptive doesn't. (D) Innate involves antibodies; adaptive involves phagocytes. **Answer:** (A) Innate is present from birth; adaptive develops after exposure. **Reason:** Innate immunity (skin, tears, WBCs) is always ready; adaptive immunity (B cells, T cells, antibodies) develops after antigen exposure. --- **Question 13.** A 25-year-old shows CD4⁺ T-cell count of 150 cells/mm³ and is diagnosed with *Pneumocystis jirovecii* pneumonia. Which stage of HIV infection is this person in? (A) Acute phase (B) Asymptomatic phase (C) AIDS (D) Post-treatment viral suppression **Answer:** (C) AIDS **Reason:** AIDS is defined as CD4⁺ count <200 cells/mm³ with opportunistic infections like PCP; normal count is 500–1,500 cells/mm³. --- **Question 14.** Which of the following modes of HIV transmission has the HIGHEST viral load risk? (A) Receptive anal intercourse (B) Sharing eating utensils (C) Mosquito bite (D) Donating blood **Answer:** (A) Receptive anal intercourse **Reason:** Anal mucosa is thin and highly vascularized, with higher transmission probability; other options have no/negligible risk. --- **Question 15.** A benign tumour is best characterized by which combination of features? (A) Slow growth, localized, no metastasis, no angiogenesis (B) Rapid growth, invasive, metastasis, necrosis (C) Slow growth, metastatic, capsulated, differentiated (D) Rapid growth, localized, high mitotic rate, undifferentiated **Answer:** (A) Slow growth, localized, no metastasis, no angiogenesis **Reason:** Benign tumours are typically slow, encapsulated, and non-invasive; malignant tumours show rapid growth, invasion, and spread. --- **Question 16.** Which oncogenic virus is most strongly associated with cervical cancer in women? (A) Hepatitis B virus (HBV) (B) Human Papillomavirus (HPV), especially types 16 & 18 (C) Herpes Simplex Virus (HSV-2) (D) Cytomegalovirus (CMV) **Answer:** (B) Human Papillomavirus (HPV), especially types 16 & 18 **Reason:** HPV-16 and HPV-18 integrate into the cervical epithelial genome, inactivating p53 tumour suppressor genes, causing ~70% of cervical cancers. --- **Question 17.** A student consumes 40 mL of spirits (40% alcohol) daily. After 2 years, liver biopsy shows fatty infiltration and portal fibrosis. Which histological process is occurring? (A) Steatosis leading to cirrhosis (B) Alcoholic hepatitis with necrosis (C) Fulminant hepatic failure (D) Acute fatty liver of pregnancy **Answer:** (A) Steatosis leading to cirrhosis **Reason:** Chronic alcohol metabolism generates acetyl-CoA, promoting triglyceride deposition (steatosis), followed by inflammation and fibrosis. --- **Question 18.** Which of the following is a mechanism by which drug abuse impairs the immune system? (A) Direct suppression of CD8⁺ T cell proliferation (B) Increased cortisol, reducing lymphocyte numbers (C) Damage to lymphoid tissues (thymus, spleen) (D) All of the above **Answer:** (D) All of the above **Reason:** Drugs like opioids and cannabinoids suppress T cells, increase stress hormones, and cause direct lymphoid tissue damage. --- **Question 19.** Which vaccine strategy is most effective in eradicating a disease globally? (A) Vaccination of high-risk groups only (B) Mass vaccination achieving >95% population immunity (herd immunity threshold) (C) Vaccination at age 18+ only (D) Optional vaccination **Answer:** (B) Mass vaccination achieving >95% population immunity (herd immunity threshold) **Reason:** For measles (R₀ ≈ 12–18), herd immunity threshold = 1 − 1/R₀ ≈ 95%, protecting even unvaccinated individuals. --- **Question 20.** A TB patient on first-line anti-TB therapy (RIPE: Rifampicin, Isoniazid, Pyrazinamide, Ethambutol) for 6 months shows sputum-positive status. Which phenomenon is most likely? (A) Drug resistance (MDR-TB) (B) Poor medication adherence (C) Malabsorption of drugs (D) Immune restoration disease **Answer:** (A) or (B) — most commonly **(B) Poor medication adherence** **Reason:** Non-adherence causes treatment failure and selects resistant strains; MDR-TB is confirmed only after drug susceptibility testing.

**Question 21.** **Assertion (A):** Memory B cells can produce antibodies faster and in higher titres upon re-exposure to the same antigen compared to naive B cells. **Reason (R):** Memory B cells are already differentiated into plasma cells and do not require T cell help. (A) Both A and R are true; R is the correct explanation of A. (B) Both A and R are true; R is NOT the correct explanation of A. (C) A is true; R is false. (D) A is false; R is true. **Answer:** (C) A is true; R is false. **Reason:** Memory cells respond faster and produce higher antibody titres, but they still differentiate into plasma cells during re-exposure and remain T cell-dependent (for most antigens). --- **Question 22.** **Assertion (A):** Passive smoking (exposure to secondhand smoke) increases the risk of lung cancer and cardiovascular disease in non-smokers. **Reason (R):** Secondhand smoke contains lower concentrations of carcinogens than mainstream smoke, so it poses negligible health risk. (A) Both A and R are true; R is the correct explanation of A. (B) Both A and R are true; R is NOT the correct explanation of A. (C) A is true; R is false. (D) A is false; R is true. **Answer:** (C) A is true; R is false. **Reason:** Secondhand smoke DOES contain carcinogenic compounds (polycyclic aromatic hydrocarbons, nitrosamines) at significant concentrations, causing documented health harm. --- **Question 23.** **Assertion (A):** HIV integrates its RNA genome into the host CD4⁺ T cell chromosome using reverse transcriptase and integrase enzymes. **Reason (R):** This integration is why antiretroviral therapy (ART) can suppress viral replication but cannot completely cure HIV infection. (A) Both A and R are true; R is the correct explanation of A. (B) Both A and R are true; R is NOT the correct explanation of A. (C) A is true; R is false. (D) A is false; R is true. **Answer:** (B) Both A and R are true; R is NOT the correct explanation of A. **Reason:** Integration is accurate; however, ART failure to cure is primarily due to latent viral reservoirs in long-lived cells, not solely integration. --- **Question 24.** **Assertion (A):** A malignant tumour that has metastasized (TNM stage IV) has a worse prognosis than a localized malignant tumour (stage I). **Reason (R):** Metastatic tumours are resistant to all chemotherapy drugs and radiotherapy. (A) Both A and R are true; R is the correct explanation of A. (B) Both A and R are true; R is NOT the correct explanation of A. (C) A is true; R is false. (D) A is false; R is true. **Answer:** (C) A is true; R is false. **Reason:** Stage IV tumours do have worse prognosis, but many metastatic cancers respond to modern targeted therapy and immunotherapy; resistance is not absolute. --- **Question 25.** **Assertion (A):** The incubation period of COVID-19 (typically 5–14 days) is shorter than that of Ebola virus disease (~2–21 days). **Reason (R):** Shorter incubation periods indicate higher transmission rates and more severe initial symptoms. (A) Both A and R are true; R is the correct explanation of A. (B) Both A and R are true; R is NOT the correct explanation of A. (C) A is true; R is false. (D) A is false; R is true. **Answer:** (C) A is true; R is false. **Reason:** Incubation period is true but does NOT determine transmission rate or severity; asymptomatic transmission and viral load kinetics are more relevant. --- **Question 26.** **Assertion (A):** Vaccination against polio (IPV/OPV) generates both humoral immunity (antibodies) and cell-mediated immunity (T cells). **Reason (R):** OPV is a live attenuated vaccine that triggers T cell responses; IPV is inactivated and triggers only B cell responses. (A) Both A and R are true; R is the correct explanation of A. (B) Both A and R are true; R is NOT the correct explanation of A. (C) A is true; R is false. (D) A is false; R is true. **Answer:** (C) A is true; R is false. **Reason:** Both vaccines generate T and B cell responses; OPV is live-attenuated (stronger T cell response), but IPV also stimulates T cell help for B cells. --- **Question 27.** **Assertion (A):** Cannabis (marijuana) use in adolescents can permanently alter brain development, particularly in the prefrontal cortex and hippocampus. **Reason (R):** The endocannabinoid system regulates synaptic pruning and myelination during adolescence, which continues until age ~25. (A) Both A and R are true; R is the correct explanation of A. (B) Both A and R are true; R is NOT the correct explanation of A. (C) A is true; R is false. (D) A is false; R is true. **Answer:** (A) Both A and R are true; R is the correct explanation of A. **Reason:** THC disrupts endocannabinoid signalling during critical neurodevelopmental windows, impairing executive function and memory formation. --- **Question 28.** **Assertion (A):** Individuals with a CD4⁺ count >500 cells/mm³ and undetectable plasma viral load on ART cannot sexually transmit HIV ("Undetectable = Untransmittable"). **Reason (R):** Undetectable viral load in plasma directly implies zero viral particles in genital secretions. (A) Both A and R are true; R is the correct explanation of A. (B) Both A and R are true; R is NOT the correct explanation of A. (C) A is true; R is false. (D) A is false; R is true. **Answer:** (B) Both A and R are true; R is NOT the correct explanation of A. **Reason:** U=U is true (evidence-based), but genital viral shedding is not always perfectly correlated with plasma load; the mechanism is more complex than stated in R. --- **Question 29.** **Assertion (A):** Smoking cessation leads to measurable improvements in lung function and reduced cancer risk within 1–5 years. **Reason (R):** Smoking causes only reversible mucus plugging and inflammation; DNA damage from carcinogens is irreversible. (A) Both A and R are true; R is the correct explanation of A. (B) Both A and R are true; R is NOT the correct explanation of A. (C) A is true; R is false. (D) A is false; R is true. **Answer:** (C) A is true; R is false. **Reason:** A is true (evidence-based): FEV₁ improves, cancer risk drops 50% by 10 years. R is partially false: DNA damage is irreversible, but cell turnover and DNA repair mechanisms (e.g., p53) can limit further accumulation. --- **Question 30.** **Assertion (A):** A person receiving chemotherapy for cancer often develops immunosuppression and opportunistic infections similar to AIDS patients. **Reason (R):** Chemotherapy drugs and cancer both directly destroy CD4⁺ T lymphocytes, leading to identical immune deficiency profiles. (A) Both A and R are true; R is the correct explanation of A. (B) Both A and R are true; R is NOT the correct explanation of A. (C) A is true; R is false. (D) A is false; R is true. **Answer:** (C) A is true; R is false. **Reason:** Chemotherapy does cause immunosuppression and opportunistic infections, but the mechanism is broad cytotoxicity (not CD4⁺ specific like HIV) and differs mechanistically.

**Trap 1: Confusing Communicable & Non-Communicable Diseases.** Students often select "diabetes" when asked for a communicable disease or vice versa. **Strategy:** Remember the definition: communicable = pathogen-transmitted (TB, malaria, HIV). Non-communicable = lifestyle/genetic (cancer, diabetes, hypertension). Use the phrase "Can I catch it from someone?" If yes → communicable. **Trap 2: Pathogen Identification by Symptoms Alone.** Multiple pathogens cause fever and cough (viral pneumonia, TB, influenza). **Strategy:** Don't rely on symptoms alone. Link symptoms to specific epidemiological clues: TB → chronic cough >3 weeks + blood sputum + high-risk population. Flu → sudden onset, myalgia, low mortality. **Trap 3: Confusing Active & Passive Immunity.** Options like "antibodies from mother" (passive) are tempting when the question asks for immunity *duration*. Passive immunity lasts weeks; active lasts years. **Strategy:** Active = your body makes antibodies (vaccination, infection). Passive = you receive pre-made antibodies (serum, colostrum). Only active provides memory. **Trap 4: Mistaking Benign for Malignant Tumours.** Both "grow" and can be "solid," but benign tumours DON'T metastasize. **Strategy:** Use the mnemonic **AGIN**: *Appearance* (benign = well-differentiated; malignant = poorly differentiated), *Growth* (benign = slow; malignant = rapid), *Invasion* (benign = localized; malignant = invasive), *Necrosis* (benign = rare; malignant = common). **Trap 5: Confusing Latency & Dormancy in HIV.** HIV does not truly "sleep" in CD4⁺ cells; it integrates and is transcribed at low levels. **Strategy:** Know that "latent reservoirs" = anatomical sanctuaries (CNS, lymph nodes) where virus persists despite ART. Not the same as dormant virus. **Trap 6: Misidentifying the Correct Vaccine Age/Schedule.** Questions ask "which vaccine at birth?" Candidates confuse BCG, OPV, Hepatitis B. **Strategy:** Memorize India's National Immunization Schedule (2024-25): *Birth* = BCG + OPV/IPV + HepB; *6 weeks* = DPT + IPV + Rotavirus; *6 months* = DPT booster; *12–15 months* = MMR. **Trap 7: Assuming All Drug Abuse Damages the Same Organ.** Alcohol → liver; opioids → respiratory; stimulants → cardiac. **Strategy:** Know organ-specific targets: Alcohol = liver + brain + pancreas; Tobacco = lungs + cardiovascular; Cannabis = prefrontal cortex (adolescence); Opioids = respiratory depression. **Trap 8: Confusing AIDS Definition with HIV Infection.** All AIDS patients have HIV, but not all HIV+ patients have AIDS. AIDS = CD4 <200 cells/mm³ OR opportunistic infection. **Strategy:** HIV+ ≠ AIDS until CD4 drops below 200 or specific infections (PCP, CMV) appear. **Trap 9: Overstating the Protective Effect of Vaccines.** Vaccines don't provide 100% protection (e.g., flu vaccine ≈ 40–60% efficacy). **Strategy:** Look for phrases like "reduces risk" or "provides immunity to most strains"—not "prevents all cases." **Trap 10: Mixing Up Incubation Period & Infectious Period.** Incubation = time from exposure to symptom onset. Infectious period = when person can spread disease (often overlaps but is distinct). **Strategy:** Incubation is about the individual's symptoms; infectious period is about transmission to others.

**Pre-Exam Preparation (2 Weeks Before).** Allocate 45–60 minutes daily to MCQ practice: 15 min (easy), 25 min (medium), 15 min (hard/assertion-reason). Track which topics you miss most (e.g., HIV transmission routes, vaccine schedules). Spend extra time on weak areas. Use a timer to simulate exam pressure. **Exam Day Strategy (2–3 Hours Before).** Do NOT try new MCQs the morning of the exam. Instead, revise key definitions: immunity types, pathogen classes, disease stages. Skim the common trap list (see above section). Ensure you've eaten and slept adequately; fatigue causes reading errors. **During the MCQ Exam.** **60 seconds per question** is your rough benchmark for a 30-MCQ paper (30 min total). Allocate time by difficulty: - Easy MCQs (Q1–10): 40 seconds each (6–7 min total) - Medium MCQs (Q11–20): 60 seconds each (10 min) - Hard/Assertion-Reason (Q21–30): 90 seconds each (13–15 min) **Answer Selection Technique:** 1. **Read the question twice.** Identify the core concept being tested (e.g., "Which mode of HIV transmission?"). This prevents misreading. 2. **Eliminate obviously wrong options.** In a typical 4-option MCQ, 1–2 are clearly wrong. Eliminate these first. 3. **If unsure between 2 options:** Re-read the question stem carefully. Is it asking for "primary," "most likely," "best," or "all of the above"? These qualifiers change the answer. 4. **Flag & return strategy.** If a question takes >90 seconds, mark it mentally, answer your best guess, and return if time permits. Never leave a blank. **Assertion-Reason Technique (Qs 21–30).** These require a two-step verification: - **Step 1:** Is the Assertion true? (Yes/No) - **Step 2:** Is the Reason true AND does it explain the Assertion? Make a decision matrix: | Assertion | Reason | Correct? | Option | |-----------|--------|----------|--------| | True | True + explains | Yes | (A) | | True | True + doesn't explain | Yes | (B) | | True | False | Yes | (C) | | False | True | No | (D) | **Last 5 Minutes.** Do a final scan: Check that you haven't left blanks. Verify that your OMR sheet (if applicable) matches your answers. Do NOT change answers on a whim unless you spot a clear reading error. **Post-Exam Review.** After the exam, identify 2–3 questions you got wrong and analyze the reason: Was it a knowledge gap or a careless mistake? Record this in a personal "error log" to avoid repeating the same mistakes in your next assessment.