Free Specific Defense Mechanism MCQs with Answers

• A. Production of antibodies by plasma cells
• B. Intact skin and the mucous membranes of the body openings
• C. Activation of cytotoxic T lymphocytes
• D. Formation of memory cells after an infection

Explanation: The first line is a physical and chemical barrier that stops pathogens entering at all: unbroken skin, mucus that traps microbes, cilia…

• A. plasma cells derived from B lymphocytes
• B. cytotoxic T lymphocytes
• C. macrophages in the lymph nodes
• D. neutrophils in the blood

Explanation: When a B lymphocyte meets its matching antigen it divides, and most of the daughter cells become plasma cells packed with rough…

• A. a single polypeptide chain
• B. two identical polypeptide chains
• C. four polypeptide chains, two heavy and two light, arranged in a Y shape
• D. a chain of nucleotides folded into a Y shape

Explanation: The two arms of the Y carry the variable regions that give each antibody its specific antigen binding sites, while the constant stem…

• A. antibodies dissolved in the plasma
• B. B lymphocytes
• C. complement proteins
• D. T lymphocytes

Explanation: T cells act on cells rather than on free antigen, destroying virus infected cells, cancer cells and transplanted tissue by direct contact…

• A. helper T cells
• B. cytotoxic T cells
• C. plasma cells
• D. free antibody in the plasma

Explanation: Cytotoxic T cells recognise viral antigen displayed on the surface of an infected cell and release perforin, which punches holes in its…

• A. activate B cells and cytotoxic T cells by secreting cytokines
• B. engulf and digest bacteria
• C. secrete large amounts of antibody
• D. produce histamine during an allergic reaction

Explanation: Helper T cells sit at the centre of the response, recognising antigen presented by macrophages and then releasing chemical signals that…

• A. the antigen is weaker the second time
• B. the skin has become impermeable to that pathogen
• C. memory cells produced in the first exposure are already present in large numbers
• D. antibodies from the first exposure are still circulating in the same amount

Explanation: A first exposure leaves behind long lived memory B and T cells specific to that antigen, so a second exposure finds a large clone ready to…

• A. natural passive immunity
• B. artificial passive immunity
• C. natural active immunity
• D. artificial active immunity

Explanation: It is artificial because the antigen is given deliberately rather than met by chance, and active because the person's own lymphocytes…

• A. natural passive immunity
• B. natural active immunity
• C. artificial passive immunity
• D. no immunity at all

Explanation: The baby is given ready made antibody rather than making its own, so the protection is passive, and because it comes through a natural…

• A. ready made antibodies against the pathogen
• B. killed or weakened pathogens, or antigens taken from them
• C. antibiotics that kill the pathogen
• D. living virulent pathogens in a small dose

Explanation: The point of a vaccine is to present the antigen without causing the disease, so the organism is killed, attenuated, or replaced by one of…

• A. a few minutes
• B. about an hour
• C. several days
• D. about a year

Explanation: The lag of roughly five to ten days is the time needed for the one matching lymphocyte to be selected, to divide into a clone and for…

• A. any protein made by a white blood cell
• B. a chemical that destroys bacteria directly
• C. a cell that engulfs foreign particles
• D. any molecule the body recognises as foreign and responds to by making antibodies

Explanation: Antigens are usually proteins or polysaccharides on the surface of a pathogen, a pollen grain or a transplanted cell, and their shape is…

• A. the immune system attacks the body's own tissues
• B. the body cannot make any antibody at all
• C. a virus destroys the helper T cells
• D. an allergen provokes the release of histamine

Explanation: Self tolerance breaks down and lymphocytes treat a normal body component as foreign, the synovial membrane in rheumatoid arthritis and the…

• A. complement proteins puncturing the cell membrane
• B. histamine released from mast cells
• C. cytotoxic T cells destroying the airway lining
• D. the pathogen's own toxins

Explanation: An allergen binds IgE already attached to mast cells, which then release histamine, and histamine dilates blood vessels and makes…

• A. IgA
• B. IgE
• C. IgG
• D. IgM

Explanation: IgG is the smallest and most abundant immunoglobulin in plasma and the only one transported across the placenta, so it gives the fetus and…

• A. IgG
• B. IgM
• C. IgE
• D. IgA

Explanation: IgA is secreted onto mucous surfaces and into milk, where it neutralises pathogens at the point of entry before they can invade, which is…

• A. T lymphocytes recognising the foreign antigens on the graft
• B. histamine released by mast cells
• C. phagocytosis by neutrophils alone
• D. the failure of the graft's own blood supply

Explanation: The donor tissue carries different major histocompatibility antigens, and T cells attack the graft as they would a virus infected cell…

• A. tonsils
• B. thymus gland
• C. thyroid gland
• D. tissue fluid

Explanation: Both kinds of lymphocyte originate in the bone marrow, but T cells travel to the thymus, where those that would attack the body's own…

• A. producing memory cells against bacteria
• B. binding specifically to one type of antigen
• C. digesting the cell walls of bacteria
• D. raising the body temperature during infection

Explanation: Lysozyme is an enzyme that breaks the peptidoglycan of bacterial cell walls, so the cell bursts by osmosis, and it acts on any susceptible…

• A. an Rh positive mother carries an Rh negative fetus
• B. both parents are Rh positive
• C. the mother's blood group is AB
• D. an Rh negative mother, already sensitised, carries an Rh positive fetus

Explanation: An Rh negative mother who has previously been exposed to Rh positive fetal blood makes anti D antibodies, and being IgG these cross the…