AQA A-Level Biology Paper 1, June 2023: Question 6

8 marks · Medium difficulty · Short Answer

Define genome and proteome, evaluate early bacterial classification using flagella, suggest reasons for renaming species, and calculate image magnification.

Practise this question

Question

A multi-part question starting with defining genome and proteome, followed by a text passage about early 20th-century bacterial classification using flagella. Questions 06.2 and 06.3 ask to consider limitations and reasons for renaming species. Question 06.4 includes Figure 6 showing an optical microscope image of a single bacterial cell with a flagellum, requiring a magnification calculation.
Question text

06.1 Define genome and proteome.

[2 marks]

Genome

Proteome

The classification system used in the early 20th century grouped different species of

bacteria according to the position and shape of flagella on bacterial cells and by the

number of flagella per cell. These were observed using an optical microscope.

Each species of bacterium has a characteristic cell shape and arrangement of flagella.

These characteristics may be shared with other species within a genus.

Flagella are fragile, difficult to stain and may extend from the cell at any angle.

06.2 Consider the accuracy and limitations of the early classification of bacteria using the

arrangement of flagella.

[3 marks]

06.3 Suggest why several bacterial species have been renamed in recent years.

[1 mark]

06.4 Figure 6 shows an image from an optical microscope of a single bacterial cell.

Figure 6

This bacterial cell is 2.3 μm long (excluding the flagellum).

Calculate the magnification of this image.

Show your working.

[2 marks]

Magnification ×

Mark scheme

Show the mark scheme The mark scheme provides acceptable marking points for each sub-question: 06.1 details definitions for genome and proteome; 06.2 lists limitations such as optical microscope resolution and fragile flagella; 06.3 suggests base sequencing or electron microscopes; 06.4 details the steps and expected answer range for calculating magnification.

Question Marking Guidance Mark Comments

(Genome)

1. Complete set of genes in a cell 1. Reject ‘all the

DNA/genes within a

OR species/population’

(All) the DNA in a cell

1 and 2. Accept

OR organism for cell

(All) the genes/alleles/genetic material in a

cell 2 2. For ‘full range’

06.1 accept ‘complete set’

(2 x OR all

OR AO1)

The total number of DNA bases in a 2. Do not accept

cell; ‘number of proteins’

unqualified

(Proteome)

2. (Full) range of proteins that a cell can produce

2. Ignore ‘range of

OR proteins that a

species/population

(Full) range of proteins coded for by the cell’s can produce’

DNA/genome;

1. Can not identify/distinguish species;

2. (Optical) microscope resolution is low; 2. Ignore

magnification

3. Flagella (are fragile so) broken/damaged/missing

3 max

OR 4. Ignore difficult to

06.2 (3 x

stain unqualified

Artefacts misinterpreted/mistaken for flagella; AO3)

5. Accept ‘out of

4. (Flagella) difficult to stain so not visible;

plane’ for ‘at an angle’

5. (Flagella) at an angle so not visible;

6. Not all bacteria have flagella;

DNA/mRNA/RNA base sequencing Accept genome

sequencing

OR

Amino acid sequencing

OR 1

06.3 Ignore detail OR

(AO1) magnification for

Use of electron microscopes with greater resolution

16 resolution

OR Accept abbreviations

TEM OR SEM in this

Use of electron microscopes and improved instance

staining/preparation;

Correct answer of

19 565 (from measurement of 45mm) Accept answers that

round correctly to

OR those shown

20 000 (from measurement of 46mm)

OR

20 435 (from measurement of 47mm) = 2 marks;;

06.4 (2 x

AO2) Accept division by 2.3

x 10-3 OR 0.0023

Accept for 1 mark, evidence of

45 000 OR 46 000 OR 47 000 (correct image size

in μm)

OR

÷ 2.3 (correct use of equation);

How to answer it

Bacterial Classification, Genomics & Microscopy Calculations

What this question tests

This question assesses your recall of core molecular biology definitions (genomes vs. proteomes), your ability to evaluate the limitations of historical classification methods using microscopes, your understanding of modern DNA-based taxonomy, and your practical microscopy calculation skills using standard magnification formulas and unit conversions.

Question 06.1 [2 marks]

Definitions of Genome and Proteome

✅ Correct Answer

  • Genome: The complete set of genes in a cell (or all the DNA / genetic material in a cell).
  • Proteome: The full range of proteins that a cell can produce (or proteins coded for by the cell's DNA/genome).

❌ Common Errors

  • Saying "all the DNA within a species or population" instead of a cell/organism.
  • Qualifying proteome incorrectly as just a "number of proteins" without stating it is the full range/set produced.
Question 06.2 [3 marks]

Evaluating Early Classification Using Flagella

✅ Correct Answer (Any 3)

  • Optical microscopes have low resolution, so they cannot distinguish or identify certain species clearly.
  • Flagella are fragile and easily broken, damaged, or missing during preparation.
  • Artefacts can be misinterpreted or mistaken for flagella.
  • Flagella are difficult to stain, making them invisible.
  • Flagella positioned at an angle may be out of the plane of focus and not visible.
  • Not all bacteria actually possess flagella.

🧠 Exam Technique

This is an AO3 evaluation question. You must combine biological knowledge of optical microscope limitations (wavelength of light limits resolution) with the practical physical properties of bacteria provided in the stem (fragility, staining difficulties, angles).

Question 06.3 [1 mark]

Modern Re-classification of Bacteria

✅ Correct Answer

DNA / mRNA / rRNA base sequencing, amino acid sequencing, or the use of electron microscopes with greater resolution and improved staining/preparation techniques.

💡 Key Knowledge

Modern taxonomy relies heavily on molecular phylogeny (comparing base sequences in DNA or amino acid sequences in proteins like RNA polymerase or cytochrome c) rather than observable physical characteristics (phenotypes), which can be misleading due to convergent evolution.

Question 06.4 [2 marks]

Microscopy Calculation

📐 Step-by-Step Calculation

  1. Recall the formula: Magnification = Image size ÷ Actual size ( M = I / A ).
  2. Measure the image: Using a ruler on Figure 6, measure the length of the bacterial cell in millimetres (typically between 45 mm and 47 mm, depending on print scale).
  3. Convert units: Convert mm to micrometres (µm) by multiplying by 1000.
    e.g., 45 mm = 45 000 µm.
  4. Substitute and calculate:
    45 000 µm ÷ 2.3 µm = 19 565
    (Acceptable range based on 45–47 mm measurements: 19 565 to 20 435).

❌ Common Calculation Traps

  • Unit Mismatch: Forgetting to convert image size (mm) into the same units as actual size (µm). This is the #1 reason students lose marks here!
  • Incorrect measuring: Failing to measure along the major axis of the cell accurately. Always show your measured image size clearly in your working out to secure error-carried-forward (ecf) marks.

Topics

Biology · 3.4 Genetic information, variation and relationships between organisms

Question and mark scheme from the AQA A-Level Biology examination, Paper 1, June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.