AS Level Biology chapter 11: Immunity MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
25 exam-style questions on 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 town has 12 000 people. A vaccine is given to 9 000 of them and is protective in 80% of the people who receive it. What percentage of the town is protected by the vaccine?
A
20%
B
60%
C
75%
D
80%
Show answer
Answer: B. The number protected is 9 000 × 0.80 = 7 200, and 7 200 ÷ 12 000 × 100 = 60%. 75% is the proportion vaccinated, forgetting that the vaccine does not work in everyone. Immune people also protect the unvaccinated by reducing the spread (herd immunity).
2. Why are antibody-producing plasma cells fused with myeloma cells?
A
myeloma cells remove antigens from the culture, which protects the other cells
B
plasma cells make one antibody but cannot divide, while myeloma cells divide continuously
C
plasma cells are too small to survive in culture without the larger myeloma cell
D
myeloma cells make the antibodies, while plasma cells provide the ability to divide indefinitely
Show answer
Answer: B. Fusion gives a cell that both secretes the chosen antibody and keeps dividing, so large amounts of identical antibody can be made.
3. Antibodies bind to many bacteria at once, causing them to clump together. What is this called?
A
neutralisation
B
clonal selection
C
lysis
D
agglutination
Show answer
Answer: D. Clumping is agglutination, which makes pathogens easier for phagocytes to engulf. Neutralisation blocks toxins.
4. Why do only a few of the body's B-lymphocytes respond to a particular pathogen?
A
most B-lymphocytes have already been used up in earlier responses and cannot divide again
B
only the B-lymphocytes that are in the spleen at the time of infection can respond
C
only a few have receptors complementary to the antigen, and only these are selected to divide
D
the other B-lymphocytes are destroyed by the pathogen before they can respond
Show answer
Answer: C. Each B cell has one specific receptor. Those that match the antigen are selected and divide by mitosis: clonal selection and expansion.
5. Which is the correct order of events in a primary immune response to a bacterium?
A
macrophage presents antigen → T-helper cells are activated → selected B cells divide → plasma cells secrete antibodies
B
plasma cells secrete antibodies → macrophage presents antigen → T-helper cells activated → clonal expansion of B cells
C
clonal expansion of B cells → macrophage presents antigen → T-helper activation → antibodies secreted
D
T-helper cells release cytokines → macrophage engulfs the bacterium → B cells divide → antibodies secreted
Show answer
Answer: A. Antigen presentation activates matching T-helper cells, whose cytokines stimulate the selected B cells to divide and form antibody-secreting plasma cells.
6. Some monoclonal antibodies used to treat cancer bind to a receptor found in large numbers on some cancer cells. Why does this reduce damage to healthy cells?
A
the antibody is destroyed by enzymes inside healthy cells before it can act
B
healthy cells have no receptors of any kind, so the antibody cannot bind to them
C
the antibody binds only to cells with that antigen, so few healthy cells are targeted
D
healthy cells divide too slowly for the antibody to affect them
Show answer
Answer: C. Specific binding means the treatment is directed at cells displaying the target antigen, unlike chemotherapy which affects all dividing cells.
7. During a primary immune response, what is the role of T-helper cells?
A
they engulf pathogens by phagocytosis and display antigens on their surface
B
they release cytokines that stimulate B-lymphocytes to divide and form antibody-secreting plasma cells
C
they differentiate into plasma cells that secrete antibodies against the antigen
D
they bind to body cells that display the antigen and destroy them by releasing enzymes
Show answer
Answer: B. T-helper cells release cytokines that activate B cells, macrophages and T-killer cells. Plasma cells make the antibodies.
8. What is the role of the hinge region of an antibody?
A
it binds to antigens on the surface of the pathogen with high specificity
B
it is the region that gives the antibody its specificity for one antigen
C
it lets the two binding sites bind antigens at different distances apart, as on two bacteria
D
it attaches the antibody to receptors on the plasma cell that made it
Show answer
Answer: C. The hinge lets the two arms of the Y move relative to each other, so one antibody can bind two antigens at varying distances apart, for example on two bacteria, causing agglutination.
9. In the hybridoma method, which two cells are fused to make cells that produce monoclonal antibodies?
A
a T-helper cell and a myeloma (cancer) cell that divides rapidly
B
a memory T-cell and an activated B-lymphocyte from the same person
C
two plasma cells from a mouse that has been immunised against the antigen
D
a plasma cell (activated B-lymphocyte) and a myeloma (cancer) cell that can divide indefinitely
Show answer
Answer: D. Plasma cells make one specific antibody but cannot divide; myeloma cells divide indefinitely. The hybridoma does both.
10. A newborn baby has 40 arbitrary units of maternal antibody per cm³ of blood, and this halves every 3 weeks. The baby has not met the pathogen. Which describes the concentration at 12 weeks?
A
10 units, and it keeps falling because the baby has no memory cells for this pathogen
B
2.5 units, and it keeps falling because the baby has no memory cells for this pathogen
C
5 units, and it keeps falling because the baby has no memory cells for this pathogen
D
2.5 units, and it rises again because the baby's plasma cells make more antibody
Show answer
Answer: B. Four halvings in 12 weeks give 40 → 20 → 10 → 5 → 2.5 units. Antibodies from the mother give natural passive immunity: the baby's own lymphocytes were never activated, so there are no memory cells and no new antibody is made.
25, each with the answer and a short explanation, across 2 topics: The immune system, Antibodies and vaccination. Every chapter test draws ten of them, so you can take it many times.
Is the AS Level Biology chapter 11 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.
