NEET Biology Human Health and Diseases MCQs Set 04

Answer: (a) Skin and mucous membranes

Explanation:
1. Physical barriers such as skin and mucous linings stop entry of pathogens before any cell or chemical defence is needed.
2. So the correct choice is option (a).

Teacher's Note:
1. Skin and mucus: physical barrier.
2. Fever and interferon are later, physiological and cellular defences.

Answer: (c) an agent that stimulates antibody production

Explanation:
1. An antigen is any foreign molecule that provokes the immune system to make antibodies.
2. So the correct choice is option (c).

Teacher's Note:
1. Antigens are foreign, antibodies are made by us.
2. Not every antigen is a vaccine.

Answer: (d) Natural killer cell

Explanation:
1. Monocytes, macrophages and neutrophils engulf microbes. NK cells kill infected or abnormal cells by secreting chemicals that make them burst, not by engulfing them.
2. So the correct choice is option (d).

Teacher's Note:
1. Phagocytes: neutrophils, monocytes, macrophages.
2. NK cells are lymphocytes.

Answer: (d) T-lymphocytes (thymus-derived cells)

Explanation:
1. T-cells, which mature in the thymus, carry out cell-mediated responses such as graft rejection.
2. So the correct choice is option (d).

Teacher's Note:
1. B-cells give humoral immunity.
2. T stands for thymus.

Answer: (d) thymus and bone marrow

Explanation:
1. Lymphocytes are produced and mature in the bone marrow and thymus, the primary lymphoid organs. Spleen, tonsils, lymph nodes are secondary.
2. So the correct choice is option (d).

Teacher's Note:
1. Primary: origin and maturation.
2. Secondary: antigen contact and response.

Answer: (b) IgA

Explanation:
1. IgA is found in mucous secretions, tears, saliva and colostrum.
2. So the correct choice is option (b).

Teacher's Note:
1. IgA guards body surfaces.
2. IgE is linked with allergy.

Answer: (a) phagocytosis

Explanation:
1. They are the main phagocytic white cells of the cellular barrier of innate immunity.
2. So the correct choice is option (a).

Teacher's Note:
1. Both engulf and destroy microbes.
2. Antibodies come from plasma cells.

Answer: (c) IgM

Explanation:
1. IgG crosses the placenta from mother, but IgM does not. IgM found in a newborn must have been made by the foetus itself in response to infection.
2. So the correct choice is option (c).

Teacher's Note:
1. IgG crosses placenta, IgM does not.
2. IgM is the first antibody in a primary response.

Answer: (b) 4

Explanation:
1. An antibody is H2L2: two heavy and two light chains.
2. So the correct choice is option (b).

Teacher's Note:
1. Notation H2L2.
2. Heavy chains are the longer ones.

Answer: (c) IgA

Explanation:
1. Colostrum contains abundant IgA that protects the newborn gut and respiratory surface.
2. So the correct choice is option (c).

Teacher's Note:
1. Colostrum gives passive immunity.
2. It is a natural example.

Answer: (c) a molecule that reacts specifically with an antigen

Explanation:
1. Antibodies are protein molecules (immunoglobulins) made by plasma cells that bind a specific antigen.
2. So the correct choice is option (c).

Teacher's Note:
1. They are proteins, not cells.
2. Specificity is the key property.

Answer: (c) T-lymphocytes

Explanation:
1. T-lymphocytes mature in the thymus.
2. So the correct choice is option (c).

Teacher's Note:
1. Thymus: T-cells.
2. Bone marrow: B-cells.

Answer: (d) prophylaxis

Explanation:
1. Vaccines are given before infection to prevent disease, so they are a preventive (prophylactic) measure that gives active immunity.
2. So the correct choice is option (d).

Teacher's Note:
1. Prophylaxis means prevention.
2. Vaccines give active immunity.

Answer: (a) tuberculosis

Explanation:
1. BCG (Bacillus Calmette-Guerin) is a weakened Mycobacterium strain used against tuberculosis.
2. So the correct choice is option (a).

Teacher's Note:
1. BCG: TB.
2. DPT: diphtheria, whooping cough, tetanus.

Answer: (b) individuals of the same species

Explanation:
1. An allograft transfers tissue between genetically different members of the same species. Between species it is a xenograft.
2. So the correct choice is option (b).

Teacher's Note:
1. Allo means other.
2. Autograft is within the same body.

Answer: (d) the cornea is avascular

Explanation:
1. The cornea has no blood vessels, so antibodies and immune cells hardly reach it and rejection is rare.
2. So the correct choice is option (d).

Teacher's Note:
1. No blood supply means little immune attack.
2. Rejection is the main problem in organ grafts.

Answer: (b) active immunity

Explanation:
1. DPT gives the body weakened or inactivated antigens, so the body makes its own antibodies and memory cells.
2. So the correct choice is option (b).

Teacher's Note:
1. Active: own antibodies.
2. Passive: ready-made antibodies.

Answer: (d) memory of the immune system

Explanation:
1. Memory B and T cells formed after the first encounter respond quickly and strongly to the same antigen later.
2. So the correct choice is option (d).

Teacher's Note:
1. Secondary response is faster.
2. Memory cells are the basis.

Answer: (a) It is produced by recombinant DNA technology

Explanation:
1. The vaccine contains the viral surface antigen made by genetically engineered yeast, not the whole pathogen.
2. So the correct choice is option (a).

Teacher's Note:
1. It is the first recombinant vaccine.
2. Safe: no whole virus.

Answer: (a) diseases present from birth

Explanation:
1. Congenital means present at birth, for example Down syndrome or colour blindness.
2. So the correct choice is option (a).

Teacher's Note:
1. Congenital is not the same as infectious.
2. Genetic disease may or may not show at birth.

Answer: (b) Turner syndrome

Explanation:
1. Turner syndrome is 44 + XO, a monosomy of the sex chromosome, giving sterile females with female dysgenesis.
2. So the correct choice is option (b).

Teacher's Note:
1. XO = Turner.
2. XXY = Klinefelter.

Answer: (b) XXY

Explanation:
1. This is Klinefelter syndrome, 44 + XXY, a male with an extra X chromosome.
2. So the correct choice is option (b).

Teacher's Note:
1. XXY male is sterile.
2. Barr body is present.

Answer: (a) 44 + XXY

Explanation:
1. The extra X gives 47 chromosomes, 44 autosomes plus XXY.
2. So the correct choice is option (a).

Teacher's Note:
1. 47 chromosomes.
2. Small testes, gynecomastia.

Answer: (c) typhoid

Explanation:
1. The Widal test detects antibodies against Salmonella typhi in the blood.
2. So the correct choice is option (c).

Teacher's Note:
1. Typhoid: Widal.
2. Malaria: blood smear.

Answer: (b) Diphtheria

Explanation:
1. Diphtheria is caused by Corynebacterium diphtheriae and spreads between people. The others are non-infectious.
2. So the correct choice is option (b).

Teacher's Note:
1. Infectious = caused by a pathogen.
2. Others are lifestyle or metabolic disorders.