AQA GCSE Combined Science: Trilogy Biology Paper 2 (Foundation), 2023: Question 7
8 marks · Standard Demand difficulty · Extended Answer
Explain how the evolution of antibiotic-resistant bacteria can be slowed down and identify evidence for extinct species.
Practise this questionQuestion
Question text
07 It is estimated that 99.9% of all species that have ever existed are now extinct.
07.1 Why is the percentage of species that are extinct only an estimate?
[1 mark]
Tick ( ) one box.
All individuals of one species have the same genes.
Extinction is always caused by humans.
Humans have not found evidence of every species.
07.2 What evidence is used to study species that have become extinct?
[1 mark]
07.3 A bacterium called Clostridioides difficile (C. difficile) can infect the
human digestive system.
C. difficile can multiply and produce toxins. The toxins cause diarrhoea.
Doctors are concerned that new strains of C. difficile may evolve.
Antibiotics may not be able to kill these new strains.
Explain how the evolution of antibiotic resistant C. difficile can be slowed down.
[6 marks]
Mark scheme
Show the mark scheme
Question 7
AO /
Question Answers Extra information Mark
Spec. Ref.
07.1 humans have not found 1 AO3
evidence of every species 4.6.3.2
4.6.3.3
AO /
Spec. Ref.
07.2 fossils allow fossil record 1 AO1
allow remains of organisms 4.6.3.1
allow DNA 4.6.3.2
do not accept fossil fuels 4.6.3.3
AO /
Question Answers Mark
Spec. Ref.
Level 3: Relevant points (reasons / causes) are identified, given in 5–6
07.3 AO2
detail and logically linked to form a clear account.
Level 2: Relevant points (reasons / causes) are identified, and 3–4 AO2
there are attempts at logical linking. The resulting account is not
fully clear.
Level 1: Points are identified and stated simply, but their relevance 1–2 AO1
is not clear and there is no attempt at logical linking.
No relevant content 0
4.6.3.4
Indicative content
4.6.3.1
Methods of reducing rate of evolution and linked explanation
4.6.2.2
• doctors should not prescribe antibiotics inappropriately
o so fewer C. difficile are exposed to antibiotic(s)
• do not use antibiotics to treat mild (bacterial) infection
o because the immune system can respond (to mild bacterial
infection)
• do not use antibiotics to treat (any) viral infections
o because antibiotics do not kill viruses
• patients should complete their course of antibiotics
o so (more likely that) all C. difficile are killed
o so none survive to mutate (and form resistant strains)
• the agricultural use of antibiotics should be restricted
o so fewer C. difficile are exposed to antibiotic(s)
22 • hand washing after going to toilet
o will reduce spread of C. difficile
• people with diarrhoea / C. difficile should stay away from school /
work
o to reduce spread of C. difficile
• develop new antibiotic against C. difficile
o so all C. difficile are killed
o so none survive to mutate and form (another) resistant
strain
• develop vaccine against C. difficile
o would decrease the use of antibiotics
For Level 3, answers must refer to method(s) and linked
explanation(s).
Total Question 7 8
How to answer it
Extinction and Antibiotic Resistance
What this question tests
This question assesses your understanding of biodiversity, the fossil record, and the evolution of antibiotic resistance. You need to show you understand why scientific data can be uncertain and provide a structured explanation of how medical and agricultural practices affect bacterial evolution.
Estimating Extinction
Correct Answer
Humans have not found evidence of every species.
Key Knowledge
- Many species were soft-bodied and left no fossils.
- Fossils may have been destroyed by geological activity.
- Many fossils are still buried deep underground.
Evidence for Extinction
Correct Answer
Fossils
Also accepted: Remains of organisms, DNA.
Common Error
Do NOT write "fossil fuels". Fossil fuels (coal, oil, gas) are the remains of organisms, but they are used for energy, not for studying the specific anatomy of extinct species.
Slowing Down Antibiotic Resistance
6-Mark Extended Response
Exam Technique: The "Method + Reason" Rule
To reach Level 3 (5-6 marks), you must provide a method to slow evolution AND a linked explanation for why it works. Simply listing facts will limit you to Level 1 or 2.
1. Medical Practice
- Method: Doctors should not prescribe antibiotics for viral infections or mild bacterial infections.
- Reason: Antibiotics do not kill viruses. Reducing use means fewer bacteria are exposed to the drug, reducing the "selection pressure" for resistance.
2. Patient Responsibility
- Method: Patients must complete the full course of antibiotics.
- Reason: This ensures all bacteria (including the slightly more resistant ones) are killed, so none survive to mutate and multiply.
3. Farming & Hygiene
- Method: Restrict the use of antibiotics in agriculture (animal feed).
- Method: Improve hygiene (hand washing) and isolate infected patients.
- Reason: This prevents the spread of resistant strains to other people.
Examiner Commentary
Top-tier students mentioned that C. difficile is a bacterium, so it is unaffected by antivirals, and that developing new antibiotics or vaccines is a valid way to stay ahead of evolution.
Common Misconception
The human body does NOT become resistant to antibiotics. It is the bacteria that evolve resistance through mutations in their DNA. Avoid saying "people become immune to the medicine."
- ✅ Did I mention completing the full course?
- ✅ Did I explain that antibiotics don't work on viruses?
- ✅ Did I link hygiene to "reducing the spread"?
- ✅ Did I use the term "mutation" or "selection pressure"?
Topics
Biology · B6: Inheritance, Variation and Evolution · B3: Infection and Response
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Biology Paper 2 (Foundation), 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.