IGCSE · Practice questions · Antibodies and vaccination

Remember the shape.

Six original Cambridge-style questions on antigens and antibodies, the steps of vaccination, primary and secondary responses, vaccination coverage data and passive immunity in infants.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Active remembers, passive borrows.

Antigen = specific shape on the pathogen. Antibody = protein with a complementary shape.
Antibodies destroy pathogens directly or mark them for phagocytes.
Active immunity: your own antibodies, after infection or vaccination; memory cells, long-term.
Passive immunity: antibodies from another individual (placenta, breast milk); no memory cells, short-term.

Recall

[3 marks]

Extended. Outline the process of vaccination.

Weakened pathogens, or their antigens, are put into the body. ✓
The antigens stimulate an immune response by lymphocytes, which produce antibodies. ✓
Memory cells are produced that give long-term immunity. ✓

Explain

[4 marks]

Extended. Explain how antibodies help to destroy a pathogen, and why an antibody made against one pathogen does not protect against a different one.

Antibodies are proteins made by lymphocytes that bind to antigens on the pathogen. ✓
Binding leads to direct destruction of the pathogen, or marks it (and clumps pathogens together) for destruction by phagocytes. ✓
Each pathogen has its own antigens with specific shapes. ✓
An antibody has a shape complementary to only one antigen, so it cannot bind to the antigens of a different pathogen. ✓

Data

[4 marks]

Extended. The antibody level in a person's blood was measured after two exposures to the same pathogen.

	First exposure	Second exposure
Days until antibodies are detected	7	2
Peak antibody level / arbitrary units	15	120
Became ill?	yes	no

(a) Calculate how many times greater the peak was after the second exposure. (b) Explain the differences in the response.

(a) 120 ÷ 15 = 8 times greater. ✓
(b) After the first exposure only a few lymphocytes had the right shape, so antibody production was slow and the pathogen multiplied, causing illness. ✓
Memory cells were made during the first response. ✓
On second exposure the memory cells recognised the antigen at once, so antibodies were made sooner and in much larger amounts, destroying the pathogen before illness. ✓

Analysis

[4 marks]

Extended. In a town, the percentage of children vaccinated against measles fell from 95% to 70% over ten years, and cases of measles rose sharply. Explain why, including why some children who were vaccinated may be put at risk.

Vaccinated children have memory cells, so they do not become ill or pass the virus on. ✓
At 95% an infected child rarely meets an unvaccinated child, so chains of transmission break and the disease cannot spread. ✓
At 70% many more children can catch and pass on the virus, so outbreaks spread through the unvaccinated. ✓
People who cannot be vaccinated (very young babies, people who are ill) are no longer protected by the vaccinated majority; and a few vaccinated people may not have made a full response. ✓

Explain

[3 marks]

Extended. Explain the importance of breast-feeding for the development of passive immunity in infants.

Breast milk contains antibodies made by the mother. ✓
These give the infant immediate protection against pathogens the mother has met, while its own immune system is still developing. ✓
This is passive immunity: it is short-term, because no memory cells are made and the antibodies are gradually broken down. ✓

Recall

[4 marks]

Extended. Compare active immunity and passive immunity. Give two similarities or differences in each of: the source of the antibodies, and how long protection lasts.

Both involve antibodies that bind to specific antigens on a pathogen. ✓
Active: antibodies are made by the person's own lymphocytes, after infection or vaccination. ✓
Passive: antibodies are acquired from another individual, for example across the placenta or in breast milk. ✓
Active immunity is long-term because memory cells are made; passive immunity is short-term because no memory cells are made. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.