AQA AS Level Biology Paper 1, June 2024: Question 4

7 marks · Medium difficulty · Practical Techniques & Data Analysis

Complete a table showing DNA features in prokaryotic cells, nuclei and chloroplasts, then use a bar chart to calculate the percentage of deaths involving causal E. coli and identify an incorrect mathematical step, and finally choose the best method for decreasing the frequency of antibiotic-resistant bacteria in human populations.

Practise this question

Question

The question image shows three parts. First is a 3-mark table asking students to tick whether each DNA feature is found in DNA in a prokaryotic cell, nucleus, and chloroplast; the features are that DNA is circular, contains four different types of nucleotide, and is associated with histones. Second is a bar chart labelled Figure 5 showing numbers of deaths in millions, with two bars: associated E. coli at about 0.72 million and causal E. coli at about 0.18 million, alongside a question asking the student to calculate the percentage of deaths involving causal E. coli among deaths where antibiotic-resistant E. coli were present and to identify the incorrect mathematical step. Third is a 1-mark multiple-choice question asking which method is most likely to decrease the frequency of antibiotic-resistant bacteria in populations of people, with options about lower antibiotic doses, testing more people, and vaccinating more people to achieve herd immunity.
Question text

04.1 Complete Table 3 to show whether the feature of DNA is associated with the DNA

molecule found in each of these locations.

Tick ( ) the appropriate boxes.

[3 marks]

Table 3

Location of DNA molecule

Feature of DNA

Prokaryotic cell Nucleus Chloroplast

Is circular

Contains four

different types of

nucleotide

Is associated with

histones 12

Some strains of the bacterium, Escherichia coli, are known to be resistant to

antibiotics.

Scientists analysed data recording the deaths of people in hospitals across the world

during 2019.

They used the data to find how many of the bodies of people who died in hospitals

contained antibiotic-resistant E. coli bacteria and whether the E. coli were:

• not the cause of death (associated E. coli)

• the cause of death (causal E. coli).

Figure 5 shows their results.

Figure 5

04.2 Using Figure 5, a student calculated that out of all the people who died when

antibiotic-resistant E. coli were present, 25% of those deaths involved causal E. coli.

The student’s calculation is incorrect.

Use Figure 5 to calculate the correct percentage of deaths involving causal E. coli in

people who died when infected with antibiotic-resistant E. coli.

Identify the mathematical step the student performed incorrectly in their calculation.

[3 marks]

Correct answer %

Incorrect mathematical step

04.3 Which method is most likely to be successful in decreasing the frequency of

antibiotic-resistant bacteria in populations of people?

Tick ( ) one box.

[1 mark]

Give people lower doses of antibiotics to treat disease.

Test more people to determine if they are infected with

antibiotic-resistant bacteria.

Vaccinate more people to reach herd immunity against bacteria

that cause diseases common in human populations.

Mark scheme

Show the mark scheme The mark scheme shows the DNA table answer with ticks indicating that circular DNA applies to prokaryotic cells and chloroplasts, four different nucleotides applies to all three locations, and association with histones applies only to the nucleus. For the graph calculation, it accepts 20% as the correct percentage, or credit for using the correct values 0.72 and 0.18 or the total 0.9, and gives a method mark for identifying that the denominator should be 0.9 rather than 0.72. For the final multiple-choice question, the correct answer is to vaccinate more people to reach herd immunity against bacteria that cause diseases common in human populations.

Question Marking Guidance Mark Comments

1, 2 and 3. Mark in rows;;;

Prokaryote 3

Nucleus Chloroplast

04.1 cell (3 x

AO1)

1. and 2. Correct calculated answer of 20(%) = 2

marks;;

1. and 2. incorrect calculated answer but evidence

of 0.72 / 720 000 and 0.18 / 180 000(correct

readings from the Figure) = 1 mark

OR

0.9 / 900 000 (correct total number of deaths) = 1

mark

OR

Correct calculation using incorrect graph readings

= 1 mark

OR 3

04.2 (3 x

0.2 (correct answer but not expressed as a

AO3) 3. Accept used 0.72 if

percentage) = 1 mark;

0.9 is also shown as

the denominator in the

calculation

(Incorrect mathematics step)

3. Accept divided by

3. Used 0.72 not 0.9 (as denominator) for denominator

OR 3. Accept the incorrect

0.9 was not the denominator calculation shown e.g.

0.18 ÷ 0.72

OR

3. Accept description

0.72 was the denominator = 1 mark;

of incorrect method

e.g. ‘The associated

not the total is used’

Vaccinate more people to reach herd immunity 1

04.3 against bacteria that cause diseases common in (1 x

human populations. AO3)

How to answer it

DNA Structure, Data Analysis & Antibiotic Resistance

What this question tests

This question assesses your knowledge of organelle DNA characteristics (comparing prokaryotes, nuclei, and chloroplasts), your ability to interpret epidemiological bar charts involving multi-category totals, your data-handling skills in percentage calculations, and your understanding of disease prevention strategies regarding antibiotic resistance.

Question 04.1

Comparing DNA Features Across Cell Locations

✅ Correct Answer (Mark Scheme Table)

  • Is circular: Tick for Prokaryotic cell and Chloroplast. (Nucleus DNA is linear).
  • Contains four different types of nucleotide: Tick for all three locations (A, T, C, G are universal across cellular life).
  • Is associated with histones: Tick for Nucleus only. (Prokaryotes use basic proteins like-histones, not true histones; chloroplasts have naked circular DNA).

💡 Key Knowledge

  • Prokaryotic DNA and chloroplast/mitochondrial DNA are short, circular, and free from histones.
  • Eukaryotic nuclear DNA is long, linear, and tightly wound around histone proteins to form chromosomes.
  • All known cellular DNA uses the same four nucleotide bases (Adenine, Thymine, Cytosine, Guanine).
🎯 Marks available: 3 marks (1 mark per correct row).
Question 04.2

Data Calculation and Identifying Errors

📐 Step-by-Step Calculation

  1. Read Figure 5 carefully:
    Causal E. coli deaths = 0.18 million (or 180,000)
    Associated E. coli deaths = 0.72 million (or 720,000)
  2. Calculate the total population who died with antibiotic-resistant E. coli present:
    Total = 0.18 + 0.72 = 0.9 million (900,000)
  3. Calculate the percentage involving causal E. coli:
    (0.18 ÷ 0.9) × 100 = 20%

❌ Common Errors & Incorrect Mathematical Step

  • The Trap: The student calculated 0.18 ÷ 0.72 = 25%.
  • The Error to State: The student used 0.72 (the associated deaths) instead of 0.9 (the total deaths) as the denominator, OR they failed to add the two categories together to find the true total population.

🧠 Exam Technique

When dealing with charts where bars represent subsets or overlapping categories, always check whether you need to sum values to find the grand total before working out proportions or percentages.

🎯 Marks available: 3 marks (2 for correct calculation/evidence of reading values, 1 for identifying the incorrect math step).
Question 04.3

Controlling Antibiotic Resistance

✅ Correct Answer

Tick the bottom box: "Vaccinate more people to reach herd immunity against bacteria that cause diseases common in human populations."

💡 Why the other options fail

  • Giving lower doses of antibiotics: This promotes selection for resistance (sub-lethal doses allow resistant mutants to survive and reproduce).
  • Testing more people for resistance: This is a diagnostic strategy, not an active method of decreasing the frequency of resistance in the population on its own.
🎯 Marks available: 1 mark (AO3 application).

Topics

Biology · Practical skills · 3.1 Biological molecules · 3.4 Genetic information, variation and relationships between organisms · 3.3 Organisms exchange substances with their environment · Data analysis

Question and mark scheme from the AQA AS Level Biology examination, Paper 1, June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.