AQA AS Level Biology Paper 1, June 2025: Question 5

6 marks · Medium difficulty · Short Answer

State methods for comparing genetic diversity between species, describe valid leaf sampling techniques, and calculate the percentage uncertainty of a leaf length measurement.

Practise this question

Question

Question 05 consists of three parts. Part 05.1 asks to give two ways other than observable characteristics in which genetic diversity between species can be compared (2 marks). Part 05.2 describes a student comparing mean surface area of leaves from two populations of wild cherry trees, asking to describe and explain how to collect these leaves to obtain valid data (2 marks). Part 05.3 shows Figure 6, an image of a ruler marked in centimeters from 0 to 10 with millimeter subdivisions, and states a leaf was measured as 86 mm; it asks to state the uncertainty of this measurement and calculate the percentage uncertainty (2 marks).
Question text

05.1 Observable characteristics can be used to compare genetic diversity between

species.

Give two other ways in which genetic diversity between species can be compared.

[2 marks]

05.2 A student compares the mean surface area of leaves on the ground from two

populations of wild cherry trees.

Describe and explain how the student should collect these leaves to obtain valid data.

[2 marks]

05.3 Another student investigated the variation in leaf length using the ruler shown in

Figure 6.

Figure 6

The student measured the length of one leaf as 86 mm

State the uncertainty of this measurement and use this to calculate the percentage

uncertainty in the length measurement.

[2 marks]

Uncertainty mm

Percentage uncertainty

Mark scheme

Show the mark scheme Mark scheme for Question 05. For 05.1: 1. Base sequence of DNA; 2. Base sequence of mRNA; 3. Amino acid sequence of polypeptides/proteins (2 max). For 05.2: 1. Random sample so no bias; 2. Large sample/number so representative / can calculate reliable mean / sufficient for statistical test (2 marks). For 05.3: 1. Uncertainty = 1 mm; 2. Percentage uncertainty = 1.2 or 1.16 or 1.163% (2 marks, with allowance for error carried forward).

Question Marking Guidance Mark Comments

1 and 2. Only penalise

1. Base sequence of DNA;

once if the word ‘base’

2. Base sequence of mRNA; is not used

3. Amino acid sequence of (same) polypeptides/

proteins; Accept:

2 max

1. DNA hybridisation

05.1 (2 x

with reference to

AO1)

bases

3. Immunological

comparisons using

proteins/

antibodies/antigens

1. Random sample so no bias;

2. Large sample/number so representative 2. Accept ≥ 10 for

large number

OR

2. Accept

2 many/multiple but

05.2 Large sample/number so can calculate reliable (2 x

mean ignore several

AO1)

OR

Large sample /number so (sufficient) for

statistical test;

1. (Uncertainty =) 1 mm;

2. (Percentage uncertainty =) 2. Allow correct

1.2/1.16/1.163/1.1628; percentage

2 uncertainty from

(1 x student’s incorrect

05.3

AO1, 1 answer to MP1

x AO2)

e.g. if uncertainty =

0.5, the answer is

0.5814, accept correct

rounding

How to answer it

Investigating Genetic Diversity & Sampling Variation

📋 WHAT THIS QUESTION TESTS

This question assesses core practical and theoretical concepts from Topic 4 (Genetic diversity and biodiversity):

  • Molecular biology techniques for comparing genetic diversity between species beyond observable phenotypic traits.
  • Ecological & field sampling design: ensuring validity through randomised sampling and statistically robust sample sizes.
  • Mathematical practical skills: determining instrument resolution, absolute uncertainty in end-to-end measurements, and calculating percentage uncertainty.
PART 05.1 • 2 MARKS

Comparing Genetic Diversity Between Species

Identifying modern molecular methods that replace observable characteristics

✅ Correct Answers (Any Two)

  • Base sequence of DNA (or DNA hybridisation comparing bases)
  • Base sequence of mRNA
  • Amino acid sequence of identical/homologous proteins (or immunological comparisons using antibodies/antigens)

💡 Key Knowledge

Observable characteristics are often determined by multiple genes (polygenic) and influenced heavily by the environment. Comparing nucleotide or polypeptide sequences provides direct quantitative evidence of evolutionary relationships.

🧠 Exam Technique

Always include the word "sequence" alongside the macromolecule. If discussing nucleic acids, you must specify "base sequence" rather than just "DNA structure".

❌ Common Errors

  • Writing just "DNA" or "genes" without mentioning sequence or bases.
  • Writing "sequence of proteins" without specifying amino acids.
  • Referring back to observable anatomical/morphological traits, which the question explicitly excluded.
Mark Scheme Note: Award 1 mark each for any two distinct valid molecular methods. The mark scheme instructs examiners to "only penalise once if the word 'base' is not used" when mRNA or DNA is referenced.
PART 05.2 • 2 MARKS

Sampling Leaves for Valid Comparison

Methodology: Describe the collection method and explain how it ensures validity

✅ Correct Answer Pairs (Max 2 marks)

The prompt asks to describe AND explain:

  • Description: Collect a random sample (e.g. using a grid and random coordinate generator).
    Explanation: To avoid/eliminate bias. [1 mark]
  • Description: Collect a large sample / large number of leaves (≥ 10 leaves).
    Explanation: To ensure the sample is representative / to calculate a reliable mean / to provide enough data for a statistical test. [1 mark]

🧠 Exam Technique: "Describe and Explain"

When asked to "describe and explain" sampling methods, always match the action to its scientific purpose:

  • Action: Random sampling → Purpose: Removes bias.
  • Action: Large sample size → Purpose: Increases reliability / ensures representativeness.

❌ Common Misconceptions

  • Confusing reliability with accuracy or validity. Saying "a large sample makes it accurate" receives NO credit.
  • Stating "collect several leaves" — the word "several" is too vague; use "a large sample" or a specific number (e.g., 20+).
  • Forgetting to explain why random sampling is used (omitting "to avoid bias").
Mark Breakdown: 1 mark for linking random sampling to the removal of bias; 1 mark for linking a large sample to representativeness, mean reliability, or running a valid statistical test (such as a Student's t-test).
PART 05.3 • 2 MARKS

Measurement Uncertainty Calculation

Determining ruler reading uncertainty and percentage uncertainty

📐 Step-by-Step Calculation

1
Find the absolute uncertainty:
The ruler markings have minor divisions of 1 mm (0.1 cm). Because measuring the length of an object with a standard ruler requires aligning the '0' mark at one end and reading the scale at the other, there is an uncertainty of ±0.5 mm at each end:
Total Uncertainty = 0.5 mm + 0.5 mm = 1 mm
2
Calculate percentage uncertainty:
% Uncertainty = (Uncertainty ÷ Measured value) × 100
% Uncertainty = (1 mm ÷ 86 mm) × 100 = 1.16279... %
3
State to an appropriate number of figures:
Acceptable answers: 1.2% , 1.16% , 1.163% , or 1.1628%

✅ Final Values

  • Uncertainty: 1 mm [1 mark]
  • Percentage uncertainty: 1.2% or 1.16% [1 mark]

❌ Common Calculation Traps

  • Using 0.5 mm: Forgetting that a ruler requires two judgements (one at 0 mm and one at 86 mm), meaning the uncertainties combine: 2 × (±0.5 mm) = 1 mm.
  • Unit mismatches: Dividing 1 mm by 8.6 cm without converting units first. Always ensure both values are in the same units (either mm or cm).
  • Note on error carried forward (ECF): If you stated an uncertainty of 0.5 mm, you can still gain mark 2 if your percentage uncertainty is correctly calculated as (0.5 ÷ 86) × 100 = 0.58% .
Mark Breakdown: MP1 = 1 mm (1 mark); MP2 = 1.2% / 1.16% / 1.163% (1 mark). Allow error carried forward from an incorrect uncertainty in MP1.

Topics

Biology · Practical skills · 3.4 Genetic information, variation and relationships between organisms · Experimental design · Uncertainty and evaluation

Question and mark scheme from the AQA AS Level Biology examination, Paper 1, June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.