AQA A-Level Biology Paper 1, November 2021: Question 6

7 marks · Medium difficulty · Practical Techniques & Data Analysis

Calculate the rate of movement of centromeres during phase E from the graph and name the three phases of mitosis, describing the role of spindle fibres and chromosome behavior in each.

Practise this question

Question

Figure 7 shows a line graph of the mean distance between centromeres and poles in micrometers against time in seconds during mitosis, divided into three phases labelled C, D, and E. Question 06.1 asks to calculate the rate of movement of centromeres during phase E in micrometres per minute to 3 decimal places. Question 06.2 asks to name the three phases of mitosis shown by C, D, and E and describe the role of spindle fibres and chromosome behaviour during each.
Question text

06.1 Figure 7 shows the mean distance between centromeres and the poles (ends) of the

spindle during mitosis.

Figure 7

Calculate the rate of movement of the centromeres during phase E.

Give your answer in μm minute–1 and to 3 decimal places.

[2 marks]

19 μm minute–1

06.2 Name the three phases of mitosis shown by C, D and E on Figure 7.

Describe the role of the spindle fibres and the behaviour of the chromosomes during

each of these phases.

[5 marks]

C

D

E

Mark scheme

Show the mark scheme The mark scheme provides answers for questions 06.1 and 06.2. For 06.1, the correct answer is 1.286 for 2 marks, with acceptable alternative working shown. For 06.2, marking guidance lists C as prophase, D as metaphase, and E as anaphase, along with specific marking points detailing chromosome condensation, attachment to spindle fibres, alignment at the equator, division of centromeres, and movement towards poles.

Question Marking Guidance Mark Comments

06.1 Correct answer for 2 marks, 1.286;;

Accept for 1 mark,

1.28571429 (correct answer not to 3 decimal

places)

OR

1.285 (incorrect rounding to 3 decimal places)

OR

Evidence of 0.02142857

OR

Evidence of 19 and 4 and 700

OR

Evidence of 15 and 1800 and 2500

OR

Evidence of 15 and 700

If mark point 1 is not

06.2 1. C = prophase and

credited = 4 max

D = metaphase and

Do not carry forward

E = anaphase; error from 1.

Accept letters for

2. (In) prophase, chromosomes condense;

stages as indicated in

1.

3. (In) prophase OR metaphase, centromeres

attach to spindle fibres; 2. Accept chromatin

for ‘chromosomes’

4. (In) metaphase, chromosomes/pairs of 5 max and for ‘condense’,

chromatids at equator/centre of spindle/cell; shorten and thicken

5. (In) anaphase, centromeres divide; 6. Accept for

‘chromatids’,

chromosomes but

6. (In) anaphase, chromatids (from each pair) reject homologous

pulled to (opposite) poles/ends (of cell); chromosomes

7. Accept for ‘shorten’,

7. (In) prophase/metaphase/anaphase, spindle

contract

fibres shorten;

How to answer it

Mitosis: Spindle Fibres, Centromeres, and Rate Calculations

What this question tests

This question assesses your ability to interpret graphical data related to cell division, calculate biological rates involving unit conversions (seconds to minutes), and recall detailed knowledge of chromosome behavior and spindle fibre mechanics across specific phases of mitosis (prophase, metaphase, and anaphase).

Question 06.1 [2 marks]

Calculate the rate of movement of the centromeres during phase E. Give your answer in um minute⁻¹ and to 3 decimal places.

✅ Correct Answer

1.286 (Awarded full 2 marks)

Mark breakdown: 2 marks total for the correct final rounded value, or 1 mark for unrounded calculation values (e.g., 1.28571429) or correct intermediate values showing working out.

📐 Step-by-Step Calculation

  1. Identify phase E on the graph: Phase E spans from time = 1800 s to 2500 s.
  2. Determine distance change (Δy): At 1800 s, distance = ~19 um. At 2500 s, distance = ~4 um. Change = 19 - 4 = 15 um.
  3. Determine time change (Δt): 2500 s - 1800 s = 700 s.
  4. Calculate rate in um s⁻¹: 15 um ÷ 700 s = 0.02142857 um s⁻¹.
  5. Convert seconds to minutes (× 60): 0.02142857 × 60 = 1.28571429 um minute⁻¹.
  6. Apply rounding: Round to 3 decimal places to get 1.286 .

❌ Common Errors & Traps

  • Unit conversion omission: Forgetting to multiply by 60 to convert from seconds to minutes (yielding ~0.021).
  • Incorrect rounding: Rounding 1.2857... down to 1.285 instead of correctly rounding up to 1.286 .
  • Reading graph values incorrectly: Misreading the start/end points on the x or y axes due to fine grid scaling.
Question 06.2 [5 marks max]

Name the three phases of mitosis shown by C, D and E on Figure 7. Describe the role of the spindle fibres and the behaviour of the chromosomes during each of these phases.

✅ Correct Marking Points (5 Max)

  • 1. Identification: C = Prophase, D = Metaphase, E = Anaphase. (Must be correct to access full marks; 4 max if incorrect).
  • 2. Prophase: Chromosomes condense / shorten and thicken (accept chromatin).
  • 3. Attachment: Centromeres attach to spindle fibres (in prophase or metaphase).
  • 4. Metaphase: Chromosomes / pairs of chromatids line up at the equator/center of the spindle/cell.
  • 5. Anaphase: Centromeres divide.
  • 6. Anaphase Movement: Chromatids (from each pair) are pulled to opposite poles/ends of the cell.
  • 7. Spindle Mechanics: Spindle fibres shorten / contract.

💡 Key Knowledge Bank

  • Phase C (Prophase): Chromosomes become visible as they coil and condense. Spindle apparatus begins to form.
  • Phase D (Metaphase): A stable plateau on the graph where centromeres maintain a fixed distance from the poles while aligning at the metaphase plate.
  • Phase E (Anaphase): Rapid decrease in distance between centromeres and poles as sister chromatids are pulled apart.

🧠 Exam Technique

  • Structured Answers: Use clear subheadings for C, D, and E to ensure the examiner can easily match your descriptions to the correct phase.
  • Precision in Terminology: Use precise biological terms. Write "chromatids" when describing anaphase separation, and avoid forbidden conflations like "homologous chromosomes" (which separate in meiosis, not mitosis).

Topics

Biology · 3.2 Cells

Question and mark scheme from the AQA A-Level Biology examination, Paper 1, November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.