AQA AS Level Biology Paper 1, June 2022: Question 9
10 marks · Medium difficulty · Short Answer
Analyze blood gas composition in the fetus versus mother, explain fetal protection via maternal IgG antibodies, discuss herd immunity and vaccination effects against measles and tetanus, and explain the immunological basis of booster vaccinations.
Practise this questionQuestion
Question text
09 Read the following passage.
The placenta is a specialised exchange surface.
In the placenta, substances are exchanged between the blood of a fetus and
the blood of its mother. Gas exchange for the fetus occurs in the placenta.
There is also transfer of IgG antibodies in the placenta between the mother’s
blood and fetal blood. These IgG antibodies protect the fetus against the 5
pathogens that infect its mother during pregnancy. The IgG antibodies can
circulate at high concentration in the mother’s blood for months or years. A
fetus does not produce IgG antibodies.
The UK immunisation programme vaccinates as many babies as possible to
protect the UK population against pathogens such as measles viruses and 10
tetanus bacteria. Measles viruses spread quickly from infected people.
Despite the efforts of the NHS, there has been a recent increase in the number
of children catching measles.
Tetanus bacteria enter the body through skin wounds. Tetanus bacteria do not
spread from infected people. In order to develop good immunity against 15
tetanus, children are given three tetanus vaccinations at regular intervals
before they reach their first birthday.
Use the information in the passage and your own knowledge to answer the
following questions.
09.1 Gas exchange for the fetus occurs in the placenta (line 3).
Describe how the composition of blood in the pulmonary artery of a fetus is different
from the composition of blood in the pulmonary artery of its mother.
Give one reason for this difference.
[2 marks]
09.2 Explain how a fetus is protected against the pathogens that infect its mother during
pregnancy (lines 5–6).
Do not give details of an active immune response in the mother.
[3 marks]
09.3 Suggest how vaccinating as many babies as possible protects the UK population
against pathogens such as measles viruses and tetanus bacteria (lines 9–11).
[2 marks]
Protection against measles
Protection against tetanus
09.4 Suggest why there has been a recent increase in the number of children catching
measles (lines 12–13).
[1 mark]
09.5 Explain why giving children more than one tetanus vaccination develops good
*21* immunity against tetanus (lines 15–17).
[2 marks]
Mark scheme
Show the mark scheme
Question Marking Guidance Mark Comments
09.1 1. Fetal blood has more oxygen 1. Accept converse for
references to
OR mother’s pulmonary
artery
Fetal blood has less carbon dioxide;
1. Accept fetal blood
2 is oxygenated
2. (Because) gas exchange occurs in the (2 x AO2)
placenta 1. Accept high for
‘more’ OR low for
OR ‘less’
1. Ignore affinity
Gas exchange does not occur in (fetal) lungs;
09.2 1. (IgG) antibodies (from mother) are 1. Accept Antibodies
complementary/bind specifically; bind with antigens /
antigen-antibody
2. To pathogens/antigens crossing the complex
placenta;
3. Giving passive immunity (in fetus)
OR (3 x AO2)
Stopping symptoms forming (in fetus)
OR
Giving immediate/rapid protection (in fetus);
09.3 (Against measles)
1.Accept ‘herd effect’
1. (To achieve) herd immunity to reduce
for herd immunity
spread;
(Against tetanus) 2
(2 x AO2)
2. No herd immunity 2. Accept Only
protects the individual
OR
Skin wounds are common (in children); – LOGY – – JUNE 2022
09.4 Accept ‘more
Reduced vaccination (in children) unvaccinated
individuals entering
1 the country/
OR
(AO2) population’
virus has mutated; Reject disease
mutated
09.5 1. (Production of) more memory cells; Ignore active
immunity
2. (So) higher concentration of antibodies (in
2. Accept More
blood)
2 antibodies (in blood)
OR (2 x AO2)
(So) more rapid production of antibodies (on
further infection);
How to answer it
Biological Exchange Surfaces & Immunity Study Guide
What this question tests
This passage-based structured question assesses your understanding of gas exchange surfaces in fetuses, passive immunity via placental antibody transfer, herd immunity principles, disease transmission vectors, and the cellular basis of secondary immune responses following vaccination.
Fetal Blood Composition & Gas Exchange
Compare pulmonary artery blood composition and state one reason. (2 marks)
✅ Correct Answer
- Fetal blood has more oxygen (or less carbon dioxide) than the mother's pulmonary artery blood.
- Reason: Gas exchange for the fetus occurs in the placenta, or gas exchange does not occur in fetal lungs.
💡 Key Knowledge
- The mother's pulmonary artery carries deoxygenated blood away from her heart to her lungs.
- The fetus receives oxygenated blood directly from the placenta via the umbilical vein, meaning fetal blood arriving at tissues is richer in O₂ than maternal pulmonary blood.
🧠 Exam Technique
- Make sure you clearly state the direction of the difference (e.g., "higher oxygen in fetal blood").
- Do not confuse fetal circulation pathways with adult circulation.
❌ Common Errors
- Mentioning "hemoglobin affinity" instead of direct gas concentrations (Examiners ignore references to affinity here as it is not being asked).
Passive Immunity via the Placenta
Explain how a fetus is protected against maternal pathogens (3 marks)
✅ Correct Answer
- IgG antibodies from the mother have variable regions that are complementary/bind specifically to pathogen antigens.
- Antibodies cross the placenta into fetal blood.
- This provides passive immunity, giving immediate protection or preventing symptoms without activating the fetus's own immune system.
💡 Key Knowledge
- Passive immunity involves the introduction of antibodies from an external source.
- The fetus does not produce its own plasma cells or memory cells for these antibodies; protection is short-lived once maternal IgG degrades.
🧠 Exam Technique
- Explicitly use the term complementary when describing antibody-antigen interactions to secure top-tier AO2 credit.
- Ensure you state that the antibodies cross the exchange surface into the fetus.
❌ Common Errors
- Stating that the fetus develops active immunity or produces its own antibodies (the passage explicitly notes: "A fetus does not produce IgG antibodies").
Herd Immunity vs. Non-Contagious Pathogens
Suggest how vaccination protects the population against measles vs tetanus (2 marks)
✅ Correct Answer
- Measles: Achieves herd immunity to reduce the spread of the virus through the population.
- Tetanus: No herd immunity applies because tetanus bacteria do not spread from infected people (transmitted via environmental skin wounds).
💡 Key Knowledge
- ">
- Herd immunity relies on high vaccination rates to break chains of transmission for communicable diseases.
- Tetanus is caused by spores found in soil entering wounds; vaccinating an individual only protects that specific individual, not the wider community from a vector.
🧠 Exam Technique
- Read the passage carefully: line 15 explicitly states "Tetanus bacteria do not spread from infected people." Use this context to justify your tetanus answer.
❌ Common Errors
- Stating that herd immunity protects against tetanus. Herd immunity only applies to contagious/communicable infections.
Factors Influencing Disease Outbreaks
Suggest why there has been a recent increase in children catching measles (1 mark)
✅ Correct Answer
- Reduced vaccination rates in children (e.g., vaccine hesitancy, missed appointments), OR mutation of the measles virus.
💡 Key Knowledge
- When herd immunity thresholds drop due to fewer vaccinated individuals, susceptible pools grow, allowing R-numbers to rise.
- Antigenic changes via mutation can also occasionally bypass existing population immunity.
🧠 Exam Technique
- This is a 1-mark question requiring a concise, direct reason. Keep answers focused strictly on uptake decline or viral mutation.
❌ Common Errors
- Vague statements like "the disease mutated" without linking it to the pathogen/virus (reject "disease mutated" — must specify virus/pathogen).
Secondary Immune Response & Vaccination
Explain why multiple vaccinations develop good immunity against tetanus (2 marks)
✅ Correct Answer
- Produces more memory cells.
- Leads to a higher concentration of antibodies produced rapidly upon further infection, or a more rapid secondary immune response.
💡 Key Knowledge
- Primary responses involve initial clonal selection and expansion of B cells into plasma and memory cells.
- Subsequent booster doses stimulate remaining memory cells to divide rapidly, destroying the toxin/pathogen before symptoms develop.
🧠 Exam Technique
- Always link booster doses directly to memory cells and the speed/volume of antibody production in secondary responses.
❌ Common Errors
- Stating that the vaccine "gives antibodies" — vaccinations contain antigens (or attenuated/dead pathogens), not ready-made antibodies.
Topics
Biology · 3.2 Cells · 3.3 Organisms exchange substances with their environment
Question and mark scheme from the AQA AS Level Biology examination, Paper 1, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.