Human Health and Disease — Class 12 MCQs with Answers

Human Health and Disease — important questions & MCQs with answers (Class 12 Biology)

14 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 76 are timed and scored when you sign in.

1. Q1Easy

   Malaria is caused by:

   A.Plasmodium (protozoan)✓ Correct

   B.Bacteria

   C.Virus

   D.Fungus

   Answer: A. Plasmodium (protozoan)

   Explanation: Plasmodium, a protozoan parasite, causes malaria; the female Anopheles mosquito is the vector, not the pathogen itself — don't confuse vector with cause.

2. Q2Easy

   Vaccination provides:

   A.Innate immunity only

   B.Passive immunity

   C.Active acquired immunity✓ Correct

   D.None

   Answer: C. Active acquired immunity

   Explanation: Vaccination triggers the body's own B and T cells to make antibodies and memory cells — active acquired immunity — unlike antiserum, which is passive and ready-made.

3. Q3Easy

   Malaria in humans is caused by:

   A.Plasmodium✓ Correct

   B.Entamoeba

   C.Salmonella

   D.Wuchereria

   Answer: A. Plasmodium

   Explanation: Malaria in humans is caused by the protozoan Plasmodium, injected as sporozoites by a female Anopheles mosquito bite — the vector, not a pathogen like Wuchereria.

4. Q4Easy

   The type of immunity present from birth and non-specific is:

   A.Passive immunity

   B.Acquired immunity

   C.Active immunity

   D.Innate immunity✓ Correct

   Answer: D. Innate immunity

   Explanation: Innate immunity is present from birth and is non-specific — skin, mucus, phagocytes and interferons — acting immediately, unlike acquired immunity which needs prior exposure.

5. Q5Easy

   The vector of malaria is the female:

   A.Aedes mosquito

   B.Culex mosquito

   C.Anopheles mosquito✓ Correct

   D.Housefly

   Answer: C. Anopheles mosquito

   Explanation: Female Anopheles mosquitoes are malaria's vector, carrying Plasmodium's sexual stage; Culex carries Wuchereria (filariasis) and Aedes carries dengue — vectors are pathogen-specific.

6. Q6Easy

   Antibodies are produced by:

   A.B-lymphocytes (plasma cells)✓ Correct

   B.RBCs

   C.Platelets

   D.Neurons

   Answer: A. B-lymphocytes (plasma cells)

   Explanation: Antibodies are secreted by plasma cells, which are activated B-lymphocytes that differentiate on encountering an antigen — not by RBCs, platelets or neurons.

7. Q7Medium

   Pneumonia is caused by:

   A.Streptococcus pneumoniae✓ Correct

   B.HIV

   C.Plasmodium

   D.Plant fungus

   Answer: A. Streptococcus pneumoniae

   Explanation: Streptococcus pneumoniae (and Haemophilus influenzae) infect the alveoli, filling them with fluid — a bacterial cause, unlike malaria's protozoan Plasmodium.

8. Q8Medium

   Antibodies are:

   A.Lipids

   B.Y-shaped immunoglobulins✓ Correct

   C.Carbohydrates

   D.Steroids

   Answer: B. Y-shaped immunoglobulins

   Explanation: Antibodies are Y-shaped immunoglobulins (2 heavy + 2 light chains) secreted by plasma cells; the variable tip binds antigen, unlike the lipid/carbohydrate/steroid distractors.

9. Q9Medium

   The malarial parasite reproduces sexually in the:

   A.Female Anopheles mosquito✓ Correct

   B.Human liver

   C.Human RBCs

   D.Human kidney

   Answer: A. Female Anopheles mosquito

   Explanation: Plasmodium's sexual phase, forming a zygote then sporozoites, occurs inside the female Anopheles mosquito; the asexual phase instead occurs in the human host.

10. Q10Medium

    Cell-mediated immunity (CMI) is carried out mainly by:

    A.RBCs

    B.B-lymphocytes

    C.T-lymphocytes✓ Correct

    D.Platelets

    Answer: C. T-lymphocytes

    Explanation: T-lymphocytes carry out cell-mediated immunity, directly attacking infected or foreign cells including graft tissue — B-cells instead secrete antibodies.

11. Q11Medium

    The periodic chill and high fever of malaria are due to release of a toxin called:

    A.Insulin

    B.Histamine

    C.Interferon

    D.Haemozoin✓ Correct

    Answer: D. Haemozoin

    Explanation: Rupture of infected RBCs releases haemozoin, a toxic pigment that triggers the periodic chills and high fever cycle characteristic of malaria.

12. Q12Hard

    Cancer is essentially:

    A.Too few mutations

    B.Lack of cells

    C.Uncontrolled cell division and metastasis✓ Correct

    D.Excess oxygen

    Answer: C. Uncontrolled cell division and metastasis

    Explanation: Cancer is uncontrolled cell division from loss of contact inhibition; malignant cells go on to invade and metastasise to distant sites via blood or lymph.

13. Q13Hard

    HIV preferentially infects:

    A.CD4 T-helper cells✓ Correct

    B.RBCs

    C.Platelets

    D.Bones

    Answer: A. CD4 T-helper cells

    Explanation: HIV preferentially infects CD4-bearing helper T-lymphocytes via its envelope protein, depleting them and crippling cell-mediated immunity — not RBCs or platelets.

14. Q14Hard

    Correct sequence of Plasmodium stages in the human host is:

    A.Gametocyte → sporozoite → merozoite → liver

    B.Sporozoite → liver schizont → merozoite → RBC stages → gametocyte✓ Correct

    C.Merozoite → sporozoite → gametocyte → liver

    D.Sporozoite → gametocyte → RBC → liver

    Answer: B. Sporozoite → liver schizont → merozoite → RBC stages → gametocyte

    Explanation: Sporozoites infect liver cells first, releasing merozoites that invade RBCs; repeated RBC cycles cause symptoms, and some merozoites form gametocytes for the mosquito.

Human Health and Disease — FAQs

More Class 12 Biology chapters

• 01Sexual Reproduction in Flowering Plants
• 02Human Reproduction
• 03Reproductive Health
• 04Principles of Inheritance and Variation
• 05Molecular Basis of Inheritance
• 06Evolution

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