MDCAT Biology chapter 12: Biology · Immunity MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
28 exam-style questions on Biology · Immunity, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. A virus infects some cells of the nasal lining. Within hours, neighbouring uninfected cells become resistant to this and other viruses, long before any antibodies are made. This is due to
A
histamine released by the mast cells
B
antibodies made by the plasma cells
C
interferon released by the infected cells
D
memory cells formed in the lymph nodes
Show answer
Answer: C. Interferon is a non-specific protein released by virus-infected cells; it helps nearby cells resist viral multiplication. Antibodies and memory cells take days to appear and act against one particular virus only.
2. Which white blood cells are the most numerous in normal blood and are usually the first phagocytes to reach a site of bacterial infection?
A
neutrophils
B
eosinophils
C
monocytes
D
lymphocytes
Show answer
Answer: A. Neutrophils form the largest share of white cells and leave the capillaries quickly to engulf bacteria. Lymphocytes are not phagocytes: they make antibodies or kill infected cells.
3. Which of the following is an autoimmune disease?
A
hay fever
B
AIDS
C
tuberculosis
D
rheumatoid arthritis
Show answer
Answer: D. In rheumatoid arthritis the immune system attacks the tissues of the body's own joints. Hay fever is an allergy, AIDS is an immune deficiency caused by HIV, and tuberculosis is a bacterial infection.
4. During inflammation, an infected wound becomes swollen mainly because
A
the capillary walls become leaky and fluid passes into the tissue
B
the bacteria absorb water from the blood and grow very large
C
the phagocytes divide quickly by mitosis inside the wound
D
blood clots block the veins and stop all blood leaving the area
Show answer
Answer: A. Histamine makes capillaries more permeable, so plasma fluid with proteins and phagocytes leaks into the tissue and causes swelling. Phagocytes reach the wound by squeezing out of capillaries, not by dividing there.
5. When a B lymphocyte meets the antigen it is specific for, it divides repeatedly, and most of the new cells start secreting large amounts of antibody. These antibody-secreting cells are
A
macrophages
B
helper T cells
C
killer T cells
D
plasma cells
Show answer
Answer: D. An activated B cell produces a clone of plasma cells, which secrete antibodies, and memory B cells. T cells and macrophages do not secrete antibodies.
6. Tears, saliva and nasal mucus contain an enzyme that kills many bacteria by breaking down their cell walls. This enzyme is
A
lysozyme
B
lipase
C
amylase
D
pepsin
Show answer
Answer: A. Lysozyme hydrolyses the peptidoglycan of bacterial cell walls, so the bacteria burst. Salivary amylase digests starch and has no action on bacteria.
7. The oral polio vaccine (OPV) given in Pakistan's immunisation programme contains
A
ready-made antibodies against polio from recovered patients
B
polio toxin made harmless by heat or chemicals
C
live polio viruses weakened so that they do not cause disease
D
antiviral drugs that stop polio viruses from multiplying
Show answer
Answer: C. OPV contains live, attenuated (weakened) polioviruses that multiply harmlessly in the gut and stimulate active immunity. Polio is a virus and does not make a toxin, so a toxoid is not possible.
8. A vaccine protects a person for years mainly because it
A
kills all the pathogens already present in the body
B
causes memory cells to form against the antigen
C
supplies antibodies that stay in the blood for life
D
makes the skin and mucous membranes impermeable
Show answer
Answer: B. A vaccine acts as an antigen without causing disease, so the person's own lymphocytes respond and leave long-lived memory cells; a later infection then meets a fast secondary response. Antibody levels themselves fall within months.
9. A single Y-shaped antibody molecule is built from
A
two heavy and two light polypeptide chains
B
one heavy and one light polypeptide chain
C
four identical light polypeptide chains
D
three heavy and one light polypeptide chain
Show answer
Answer: A. Each antibody unit has two identical heavy chains and two identical light chains, held together by disulphide bonds to give the Y shape.
10. A body cell infected with a virus is recognised and destroyed directly, without the help of antibodies, by
A
killer (cytotoxic) T cells
B
plasma cells
C
memory B cells
D
helper T cells
Show answer
Answer: A. Killer T cells bind to infected (and cancerous) cells and destroy them: this is cell-mediated immunity. Helper T cells do not kill cells; they activate B cells and killer T cells.
28, each with the answer and a short explanation, across 2 topics: Innate and adaptive immunity, Types of immunity and vaccination. Every chapter test draws ten of them, so you can take it many times.
Is the MDCAT Biology chapter 12 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
