AQA GCSE Combined Science: Trilogy Biology Paper 1 (Higher), 2023: Question 7

✅ Correct answer

Any one of:

• plasmid
• chromosome
• DNA / genes

1 mark: name any correct location of genetic material.

💡 Key knowledge

• Mutations happen in genetic material.
• In bacteria, that means the chromosome or plasmids.
• Antibiotic resistance can be caused by a mutation in a gene.

🧠 Exam technique

For 1-mark recall questions, the exact word matters. “DNA” is safe, and “plasmid” or “chromosome” are also accepted.

❌ Common errors

• “nucleus” is wrong because bacteria do not have a nucleus.
• “cell wall” is not where mutations happen.

✅ Correct answer

There was no clear area around C and E, so no bacteria were killed by those antibiotics.

1 mark for identifying no clear area, 1 mark for linking this to no bacteria being killed / antibiotic did not work.

💡 Key knowledge

• A clear area around a disc is called a zone of inhibition.
• If there is no clear area, the bacteria are resistant to that antibiotic.

🧠 Exam technique

Use the evidence from the diagram directly. Top answers state what is seen and what it means.

❌ Common errors

• Writing only “C and E are resistant” without using the figure evidence may miss a mark.
• Talking about discs A, B or D is not relevant if the question asks about C and E.

✅ Correct answer

Any valid improvement such as:

• increased the concentration of antibiotic
• increased the dose of antibiotic
• left it longer
• used a different temperature
• used a different sized disc

And the result should be: a clear area seen around the disc or bacteria around the disc killed.

Marks are for describing a change to the method and then describing the expected outcome.

💡 Key knowledge

To show resistance, you would need the antibiotic to have a stronger effect, then observe whether bacteria are killed.

🧠 Exam technique

• Write one method change and one expected result.
• Link your answer to the idea of a clear zone around the disc.

❌ Common errors

• Giving an answer that does not change the method, such as “test more carefully”.
• Writing only a result with no method change.
• Saying “use a different antibiotic” when the question is about making the method show resistance to E.

✅ Correct answer

The treatment injected around the implant

1 mark for identifying the variable changed by the scientists.

💡 Key knowledge

• Independent variable = the factor deliberately changed.
• Here, the treatment type was changed between patients.

❌ Common errors

• “The ratio” is the dependent result, not the independent variable.
• “The type of bacteria” was not what was changed.

✅ Correct answer

Any one of:

• easier to obtain
• less invasive
• quicker to obtain
• fewer side effects
• less painful

💡 Key knowledge

Fat tissue can be collected more easily than bone marrow, so it is a simpler source of stem cells.

🧠 Exam technique

Give a practical advantage. If possible, compare fat tissue with bone marrow.

❌ Common errors

• “Cheaper” is not credited here.
• “Less rejection” is ignored for this mark.

✅ Correct answer

By diffusion

Reason: the concentration of antibiotic was higher in the solution than inside the cells, so it moved down a concentration gradient.

2 marks: 1 for diffusion, 1 for the concentration gradient explanation.

📐 Step-by-step science idea

1. Antibiotic is in a solution around the cells.
2. There is a higher concentration outside the cells.
3. Particles move from high to low concentration.
4. This is diffusion.

🧠 Exam technique

If the question asks for the process and a reason, you need both. Name the process first, then explain why it happens.

❌ Common errors

• Osmosis is wrong because that is only water moving.
• Active transport is wrong because the question gives a passive movement situation.
• “Translocation” is not relevant.

✅ Correct answer

From 0.09 to 0.31

1 mark for reading the lowest and highest values correctly.

💡 Key knowledge

The range means the spread from the smallest value to the largest value.

📐 How to read it

1. Look at the stem cells only data points.
2. Find the lowest result: 0.09.
3. Find the highest result: 0.31.
4. Write the range in that order.

❌ Common errors

• Writing the difference (0.22) instead of the range endpoints.
• Including the other treatment group by mistake.
• Mixing up axes and reading the wrong scale.

✅ What a good answer includes

Any two valid points, for example:

• Pros: stem cells containing antibiotic had the smallest area of infection : total tissue area
• Pros: they had the smallest range of results
• Pros: there was no overlap with the unreactive solution group, suggesting a significant effect
• Cons: only tested on 5 patients
• Cons: some results for antibiotic treatment were similar to stem cells containing antibiotic
• Cons: age / health of patients not controlled
• Cons: only tested on one type of bacterium
• Cons: only tested on one type of implant
• Cons: only collected results after 7 days
• Cons: may lead to antibiotic resistance in S. aureus bacteria

2 marks: choose any two relevant evaluation points, ideally balanced between strengths and weaknesses.

💡 Key knowledge

The graph suggests the stem cells containing antibiotic treatment may work best, but the evidence is limited because the trial was small.

🧠 Exam technique

• Use data from Figure 10 to support your judgement.
• Explain why the result is promising, but also why the conclusion is not fully secure.
• Top answers mention sample size, variation, and whether results overlap.

❌ Common errors

• Just saying “it works” without evidence.
• Only giving pros or only giving cons.
• Ignoring the small number of patients.
• Writing about cost, religion, or embryonic stem cells — these are not needed here.

💡 Key knowledge

• Resistance questions often need you to use evidence from a diagram.
• Diffusion means movement from high to low concentration.
• Independent variable = what was changed.
• Range = lowest value to highest value.

🧠 How marks are awarded

• 1-mark questions: give the exact term.
• 2-mark explain questions: name the idea and explain it.
• Evaluation questions: make a judgement and support it with data.

❌ Final traps to avoid

• Confusing mutation with natural selection.
• Using osmosis instead of diffusion.
• Forgetting to quote values from the graph.
• Giving vague answers like “it’s better” with no reason.