AQA GCSE Combined Science: Trilogy Biology Paper 1 (Higher), 2018: Question 5

Key skills

• Read a table and spot the trend.
• Use the percentage decrease formula correctly.
• Explain herd immunity in simple terms.
• Compare primary and secondary immune responses using data from a graph.

How marks are awarded

• 1-mark answers need one correct idea.
• The calculation gives method and answer marks.
• The 6-mark question rewards detailed comparison plus biological explanation.

✅ Correct answer

Any one of these:

• Not everyone would go to the doctor.
• Some cases would not be tested, diagnosed, or confirmed.
• Some samples would not be sent for analysis.

💡 Key knowledge

The table shows medically confirmed cases only. That means it does not include every person who actually had measles.

🧠 Exam technique

Use a reason linked to recording or diagnosis. The examiner accepts ideas such as misdiagnosis or a doctor making a judgement error.

❌ Common errors

• Saying only “some cases are unknown” is too vague.
• Talking about vaccines here is not answering the question.
• Do not say the data is wrong unless you explain why it is incomplete.

📐 Calculation: step by step

1. Find the decrease: 2030 - 91 = 1939
2. Divide by the original number: 1939 ÷ 2030
3. Multiply by 100: (1939 ÷ 2030) × 100 = 95.5%

Percentage decrease = 95.5%

💡 Key knowledge

The formula for percentage decrease is:

(decrease ÷ original value) × 100

Here, the original value is 2030 because that is the 2012 number.

🧠 Exam technique

• Always show your working for method marks.
• Use the starting value as the original number.
• Write the final answer with a percentage sign.

❌ Common errors

• Subtracting in the wrong order gives a negative answer.
• Using 91 as the original value is incorrect.
• Forgetting ×100 means no percentage.
• Rounding too early can lead to 95% instead of 95.5%.

✅ Correct answer

A full-mark answer should include both ideas:

• Most people are immune, so they do not become ill.
• There is less chance of non-immune or unvaccinated people being exposed to the measles virus.

💡 Key knowledge

This is herd immunity or community immunity. If many people are protected, the virus has fewer opportunities to spread from person to person.

🧠 Exam technique

Link the idea of immunity to reduced transmission. The key biological chain is:

more vaccinated people → fewer infected people → less spread → unvaccinated people are less likely to catch it

❌ Common errors

• Saying “everyone is immune” is too absolute.
• Saying “people don’t get it” without mentioning spread loses the second mark.
• You must mention the virus or pathogen, not just “it”.

✅ Correct answer: what to include

• After the vaccine injection, antibodies rise slowly and only to a low level.
• In the graph, the vaccine causes a small increase to about 0.8 arbitrary units around weeks 3–4.
• After exposure to the measles virus, antibodies rise much faster and to a much higher concentration.
• The graph shows a sharp rise to about 7.2 arbitrary units by about week 8–9.
• After exposure, the antibody level stays high for longer than after the vaccine.
• This is because memory cells from the first exposure recognise the antigen and make the correct antibodies quickly.

💡 Key knowledge

• Vaccination gives a primary immune response.
• Later exposure to the real virus triggers a secondary immune response.
• B lymphocytes and memory cells are involved in making specific antibodies.
• The immune system recognises the measles antigen more quickly the second time.

🧠 Exam technique

To reach the top level, do three things:

1. Compare the two responses.
2. Use data from the graph.
3. Explain why the second response is faster and larger.

Good comparative phrases: higher than , faster than , for longer , whereas .

❌ Common errors

• Describing only one part of the graph.
• Forgetting to mention memory cells or previous exposure.
• Using “antibodies” without saying they are specific to the antigen.
• Not quoting any data from Figure 8.

This would be in the top band because it compares, uses data, and explains the biology clearly.

Top-scoring features

• Precise reasons for undercounting in 05.1.
• Correct use of the percentage decrease formula in 05.2.
• Clear herd immunity explanation in 05.3.
• For 05.4, a well-linked comparison using numbers from the graph.

Where marks are often lost

• Writing vague phrases like “it spreads less” without explaining why.
• Doing the calculation with the wrong original value.
• Describing the graph without comparing both responses.