AQA GCSE Biology Biology Paper 2 (Foundation), November 2021: Question 8

8 marks · Low Demand difficulty · Short Answer

Identify structures and components of DNA, deduce complementary bases during replication, and calculate the mass of DNA in a gamete.

Practise this question

Question

Question 08 consists of eight parts (08.1 to 08.8). Figure 13 shows a schematic diagram of a DNA fragment consisting of a sugar-phosphate backbone and base pairs: T paired with A, C paired with G, G paired with C, and A paired with T, with a pentagon sugar ring labelled X. Figure 14 shows a replication fork where DNA is unzipping in section Z, with some unlabelled bases in the template and newly forming strand in section Y. Sub-questions ask to name chromosomes, identify the sugar and base units, label complementary bases (A, C, G, T) in Figure 14, identify DNA replication, state what genes code for (protein), calculate the DNA mass in a sperm cell given body cell DNA mass of 6 × 10^-12 g, and name meiosis as the cell division that produces sperm cells.
Question text

08 The nucleus of a cell contains DNA.

08.1 Name the structures inside the cell nucleus that contain DNA.

[1 mark]

Figure 13 shows part of a DNA molecule.

Figure 13

08.2 Name the part of the DNA molecule labelled X.

[1 mark]

08.3 What type of substances are labelled A, C, G and T in Figure 13?

[1 mark]

Figure 14 shows another section of a DNA molecule.

Figure 14

08.4 Four of the substances you named in Question 08.3 are not labelled in part Y

of Figure 14.

Label each of these substances with the correct letter, A, C, G or T.

Use information from other parts of Figure 14 to help you.

[1 mark]

08.5 What is happening to the DNA in part Z of Figure 14?

[1 mark]

Tick ( ) one box.

Differentiation

Evolution

Fertilisation

Replication 30

08.6 A gene is a length of DNA.

*29* What type of substance does a gene code for?

[1 mark]

08.7 Most human body cells contain 6 × 10–12 grams of DNA.

What mass of DNA will a human sperm cell contain?

[1 mark]

Tick ( ) one box.

6 × 10–6 grams

6 × 10–12 grams

3 × 10–6 grams

3 × 10–12 grams

08.8 What is the name of the type of cell division that produces sperm cells?

[1 mark]

Tick ( ) one box.

Binary fission

Differentiation

Meiosis

Mitosis

Mark scheme

Show the mark scheme Mark scheme for Question 08 shows 1 mark for each part: 08.1 accepts chromosome(s), chromatid(s), gene(s), or allele(s); 08.2 accepts sugar, deoxyribose, or pentose (not ribose); 08.3 accepts base(s) or named bases; 08.4 shows the unlabelled bases correctly completed using complementary base pairing (all four required for 1 mark); 08.5 is replication; 08.6 accepts protein or polypeptide; 08.7 is 3 × 10^-12 grams; 08.8 is meiosis. Total marks: 8.

AO /

Question Answers Extra information Mark

Spec. Ref.

08.1 chromosome(s) allow chromatid(s) / gene(s) / 1 AO1

allele(s) 4.6.1.4

08.2 sugar allow deoxyribose 1 AO1

allow pentose 4.6.1.5

do not accept ribose

08.3 base(s) allow nitrogenous base(s) 1 AO1

allow adenine and cytosine and 4.6.1.5

guanine and thymine

08.4 1 AO3

4.6.1.5

all four required for the mark

AO /

Spec. Ref.

08.5 replication 1 AO3

4.6.1.5

4.1.2.2

08.6 protein allow polypeptide 1 AO1

4.6.1.4

08.7 3 × 10−12 grams 1 AO2

4.6.1.2

08.8 meiosis 1 AO1

4.6.1.2

Total 8

How to answer it

DNA Structure, Function, and Cell Division

WHAT THIS QUESTION TESTS
  • Sub-cellular Organisation: Identifying chromosomes as the DNA-carrying structures in the nucleus.
  • DNA Nucleotide Anatomy: Naming parts of a nucleotide (phosphate, sugar, and bases: A, C, G, T).
  • Base Pairing Rules: Applying complementary base pairing (A with T, C with G) during DNA replication.
  • Gene Function: Recalling that genes code for sequences of amino acids to make proteins.
  • Ploidy & Math Skills: Calculating the mass of DNA in a haploid gamete (sperm) compared to a diploid body cell using standard form.
  • Cell Division: Distinguishing between meiosis (formation of gametes) and mitosis/binary fission.
QUESTION 08.1

Name the structures inside the cell nucleus that contain DNA

[1 mark] • AO1 (Recall) • Spec Ref: 4.6.1.4

✅ Correct Answers

  • chromosome(s)
  • Also allowed: chromatid(s), gene(s), allele(s)

🧠 Exam Technique

Always give the primary biological term: chromosomes. While the mark scheme generously allows "genes", naming the macro-structure containing DNA is the safest answer.

Mark scheme: 1 mark for chromosome(s).
QUESTION 08.2

Name the part of the DNA molecule labelled X

[1 mark] • AO1 (Recall) • Spec Ref: 4.6.1.5

✅ Correct Answers

  • sugar
  • Also allowed: deoxyribose, pentose

❌ Common Errors

  • Do NOT write "ribose": Ribose is the sugar in RNA, not DNA. Writing "ribose" scores 0 marks.
  • Confusing the pentagon (sugar) with the circle (phosphate).

💡 Key Knowledge: The Nucleotide Unit

A DNA nucleotide consists of three joined parts: an alternating phosphate group (represented by the small black circle) and sugar molecule (deoxyribose pentagon labelled X) forming the "backbone", attached to one of four bases.

Mark scheme: 1 mark for sugar / deoxyribose. Reject: ribose.
QUESTION 08.3

What type of substances are labelled A, C, G and T in Figure 13?

[1 mark] • AO1 (Recall) • Spec Ref: 4.6.1.5

✅ Correct Answers

  • base(s)
  • Also allowed: nitrogenous base(s)
  • Also allowed: naming all four: adenine and cytosine and guanine and thymine

🧠 Exam Technique

The question asks what type of substances they are, not their individual names. Simply writing bases is the most direct and foolproof way to secure this mark.

Mark scheme: 1 mark for base(s).
QUESTION 08.4

Label each of these substances with the correct letter, A, C, G or T in part Y of Figure 14

[1 mark] • AO3 (Application) • Spec Ref: 4.6.1.5

✅ Correct Base Labels

Looking at the four unlabelled base boxes in bracket Y from top to bottom:

  • Top-left blank (paired with C on right): G
  • Second-left blank (paired with T on right): A
  • Third-right blank (paired with G on left): C
  • Bottom-right blank (paired with A on left): T

💡 Complementary Base Pairing Rule

DNA bases always pair up in a specific way across the two strands:

  • A (Adenine) always pairs with T (Thymine)
  • C (Cytosine) always pairs with G (Guanine)

Mnemonic: Apples on Trees, Cars in Garages.

Examiner Diagram Guide: In bracket Y of Figure 14, look across the complementary strands. Where you see a blank box directly facing a labelled base, apply the rule: opposite C write G; opposite T write A; opposite G write C; opposite A write T.
Mark scheme: 1 mark for all four letters correctly identified. (All 4 required for 1 mark).
QUESTION 08.5

What is happening to the DNA in part Z of Figure 14?

[1 mark] • AO3 (Application) • Spec Ref: 4.6.1.5, 4.1.2.2

✅ Correct Choice

☑ Replication

The original double helix is unzipping and separating down the middle so that new complementary strands can form.

❌ Incorrect Distractors

  • Differentiation: Process where cells become specialised.
  • Evolution: Change in inherited traits over generations.
  • Fertilisation: Fusion of male and female gametes.
Mark scheme: 1 mark for "Replication".
QUESTION 08.6

A gene is a length of DNA. What type of substance does a gene code for?

[1 mark] • AO1 (Recall) • Spec Ref: 4.6.1.4

✅ Correct Answers

  • protein
  • Also allowed: polypeptide

❌ Common Errors

  • "Amino acid" alone: A gene codes for a sequence of amino acids that forms a specific protein. Writing just "amino acid" is often rejected or incomplete compared to "protein".
  • Writing "carbohydrate", "lipid", or "trait/characteristic".
Mark scheme: 1 mark for protein / polypeptide.
QUESTION 08.7

Most human body cells contain 6 × 10⁻¹² grams of DNA. What mass of DNA will a human sperm cell contain?

[1 mark] • AO2 (Application & Maths) • Spec Ref: 4.6.1.2

🔧 Step-by-Step Calculation

  1. Identify ploidy: Body cells are diploid (46 chromosomes). A sperm cell is a gamete and is haploid (contains half the DNA, 23 chromosomes).
  2. Halve the mass:
    Mass in sperm = (6 × 10⁻¹² g) ÷ 2
  3. Calculate:
    (6 ÷ 2) × 10⁻¹² = 3 × 10⁻¹² g

✅ Correct Choice

☑ 3 × 10⁻¹² grams

❌ Standard Form Trap

Do not divide the power of 10! Halving 6 × 10⁻¹² gives 3 × 10⁻¹² , NOT 3 × 10⁻⁶ .

Mark scheme: 1 mark for 3 × 10⁻¹² grams.
QUESTION 08.8

What is the name of the type of cell division that produces sperm cells?

[1 mark] • AO1 (Recall) • Spec Ref: 4.6.1.2

✅ Correct Choice

☑ Meiosis

💡 Meiosis vs. Mitosis Quick Check

  • Meiosis: Produces non-identical gametes (sperm and egg cells) with half the normal chromosome number (haploid).
  • Mitosis: Produces two genetically identical body cells for growth and repair (diploid).
  • Binary fission: Cell division in bacteria (prokaryotes).
Mark scheme: 1 mark for Meiosis.

Topics

Biology · B1: Cell Biology · B6: Inheritance, Variation and Evolution

Question and mark scheme from the AQA GCSE Biology examination, Biology Paper 2 (Foundation), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.