AQA A-Level Biology Paper 1, June 2022: Question 4

9 marks · Medium difficulty · Short Answer

Describe viral replication, compare cell cycles of mitosis and binary fission, complete a meiosis diagram showing non-disjunction, and evaluate a conclusion using data from a population study on meiotic errors.

Practise this question

Question

Question text

04.1 Describe viral replication.

[3 marks]

04.2 Complete Table 2 by putting a tick ( ) where the feature is part of a cell cycle

involving mitosis or a cell cycle involving binary fission.

[2 marks]

Table 2

Cell cycle involving:

Feature

mitosis binary fission

Replication of linear

DNA

Replication of circular

DNA

Produces 2 daughter

cells

Produces 4 daughter

cells

Happens in prokaryotic

cells

Happens in eukaryotic 16

cells

Figure 6 represents a cell undergoing meiosis. It shows the chromosomes in the

parent cell and in the two cells formed after the first meiotic division.

The second division of meiosis proceeds normally except that non-disjunction occurs

in the chromosome labelled N.

Figure 6

04.3 Complete Figure 6 to show the chromosomes inside the daughter cells formed after

the second meiotic division. 17

[2 marks]

Doctors studied babies born with a mutation caused by chromosome

non-disjunction during gamete formation in their mother.

They determined each mother’s age at the time of childbirth and whether the

non-disjunction happened in the first meiotic division (MM1 error) or in the second

meiotic division (MM2 error).

Figure 7 shows the doctors’ results.

Figure 7

Figure 7 not reproduced here due to third-party copyright restrictions

04.4 A student concluded that there were more mothers of age ˃37 with MM2 errors than

with MM1 errors.

Using Figure 7 and suitable calculations show why this conclusion is not valid.

[2 marks]

Mark scheme

Show the mark scheme

Question Marking Guidance Mark Comments

1. Attachment proteins attach to receptors; 3 max 1. For ‘attachment

protein’ accept

2. (Viral) nucleic acid enters cell; (3 x

gp41/gp120/

AO1)

3. Nucleic acid replicated in cell glycoprotein but

ignore ‘receptor

OR protein’ (on virus)

Reverse transcriptase makes DNA from RNA; 1. Accept bind for

attach

4. Cell produces (viral) protein/capsid/enzymes;

2. Accept references

5. Virus assembled and released (from cell); to engulfment OR

injection for enters

Ignore references to

virus DNA/RNA

04.1 incorporated into cell

genome/nucleus/

chromosomes

2. and 3. Accept

RNA/DNA/genetic

material for ‘nucleic

acid’.

4. Accept capsomeres

OR reverse

transcriptase for

protein

5. Accept lysis OR

burst OR bud off OR

emerge for released

One mark for each correct column;; 2

Cell cycle involving (2 x

Feature Mitosis Binary AO1)

fission

Replication of linear ✓

DNA

Replication of circular ✓

04.2 DNA

Produces 2 daughter ✓ ✓

cells

Produces 4 daughter

cells

Happens in prokaryotic ✓ – A-LEVEL BIOLOGY – –

cells

Happens in eukaryotic ✓

cells

(2 x

AO2)

04.3

1. 2 cells on left correct, ignore differences in

chromosome length in drawn cells;

2. 2 cells on right correct, ignore differences in–A-LEVEL BIOLOGY – –

chromosome length in drawn cells;

(Conclusion not valid because) 2

(2 x

1. (MM1) 197/197.1;

AO3)

and

2. (MM2) 83/82.8;

04.4

Correct answer for 2 marks,

114 – 114.3 (correct difference between MM1 and

MM2)

Accept for 1 mark,

14 259.2 and 345.6 (using total population size)

MM2 is 86/86.4 bigger (using population totals)

How to answer it

Viral Replication, Cell Division, and Meiotic Non-Disjunction

What this question tests

This multi-topic question evaluates your knowledge of viral replication mechanisms, comparative features of mitosis versus binary fission, applying understanding of meiosis and chromosome non-disjunction to diagrammatic problems, and performing data analysis and calculations based on epidemiological data sets.

Question 04.1 (3 marks)

Describe viral replication.

✅ Expected Answer

Attachment proteins bind to complementary receptors on the host cell membrane.
Viral nucleic acid (DNA or RNA) enters the host cell (or virus is engulfed).
Viral nucleic acid is replicated inside the host cell (or reverse transcriptase makes DNA from RNA).
Host cell synthesizes viral proteins, capsomers, and enzymes.
New virus particles are assembled and released (via lysis, budding, or exocytosis).

💡 Key Knowledge

Viruses are non-living infectious agents and cannot undergo cell division; they rely entirely on host cell machinery.
Specificity is determined by viral attachment proteins fitting specific receptor molecules on target cells.

❌ Common Errors & Examiner Warnings

Students often lose marks by stating that the "virus enters the nucleus" or that "viruses divide by binary fission." Remember: viruses inject or release their genetic material into the host cell cytoplasm/nucleus, but the virus particle itself does not divide.

Maximum 3 marks. Awarded for any 3 valid sequential description points from the mark scheme.

Question 04.2 (2 marks)

Complete Table 2 for Mitosis vs. Binary Fission

✅ Correct Table Completions

Replication of linear DNA: Tick under Mitosis
Replication of circular DNA: Tick under Binary Fission
Produces 2 daughter cells: Ticks under BOTH Mitosis and Binary Fission
Produces 4 daughter cells: Neither (leave blank)
Happens in prokaryotic cells: Tick under Binary Fission
Happens in eukaryotic cells: Tick under Mitosis

🧠 Exam Technique

Read row headings carefully. "Produces 2 daughter cells" applies to both standard cell division cycles, whereas prokaryotes reproduce strictly by binary fission using circular DNA.

2 marks total: 1 mark for each correctly completed column.

Question 04.3 (2 marks)

Complete Figure 6 (Second Meiotic Division with Non-Disjunction)

✅ Correct Diagrammatic Answer

The prompt describes non-disjunction occurring in chromosome N during the second meiotic division. In the affected line:

One daughter cell must receive both sister chromatids (draw a circle containing two attached sister chromatids, e.g., ||| or similar representation).
The corresponding sister daughter cell receives zero chromatids (draw an empty circle containing no chromosomes, e.g., 1 single line representing none/empty).
The unaffected branch on the right proceeds normally, producing two daughter cells each containing a single chromatid (| and |).

💡 Biological Background

Non-disjunction is the failure of sister chromatids (in meiosis II) or homologous chromosomes (in meiosis I) to separate properly during anaphase, leading to gametes with abnormal chromosome numbers (aneuploidy).

2 marks: 1 mark for the correct pair of cells on the left branch, 1 mark for the correct pair of cells on the right branch. Ignore minor variations in chromosome length.

Question 04.4 (2 marks)

Disproving the Student's Conclusion Using Calculations

📐 Step-by-Step Calculation Guide

To show the conclusion ("more mothers of age >37 with MM2 errors than with MM1 errors") is not valid, you must extract data from Figure 7 and calculate the correct proportions or absolute values.

Identify MM1 value: State the correct figure for MM1 errors in mothers >37 (approx. 197 or 197.1 depending on scale/data table).
Identify MM2 value: State the correct figure for MM2 errors in mothers >37 (approx. 83 or 82.8).
Compare values: Clearly state that MM1 has a higher frequency/number than MM2, thereby proving the student's conclusion false.

❌ Common Calculation Traps

Failing to explicitly state the numbers for both MM1 and MM2 from the graph.
Making a qualitative statement ("MM1 is bigger") without backing it up with the required numerical values from Figure 7.

2 marks: 1 mark for correctly quoting/calculating MM1 values, 1 mark for correctly quoting/calculating MM2 values to demonstrate that MM1 is greater than MM2.

Topics

Biology · 3.2 Cells · 3.4 Genetic information, variation and relationships between organisms

Question and mark scheme from the AQA A-Level Biology examination, Paper 1, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.