AQA AS Level Biology Paper 1, June 2023: Question 4

8 marks · Medium difficulty · Practical Techniques & Data Analysis

Calculate the volume of a naïve T cell from an electron micrograph, determine the scale factor compared to an activated helper T cell, distinguish electron microscopy features, state the role of a helper T cell, and describe the role of tRNA in translation.

Practise this question

Question

Exam question showing electron microscope images of a naïve T cell and an activated helper T cell in Figure 5, with scale bars of 2 micrometres. Part 04.1 asks to calculate the volume of the naïve T cell and compare it to the activated helper T cell volume of 463 micrometres cubed. Part 04.2 asks to state and explain one feature showing the images are from an electron microscope. Part 04.3 asks for one role of a helper T cell. Part 04.4 asks to describe the role of tRNA in translation.
Question text

04 Scientists investigated the activation of T lymphocytes.

The scientists studied two types of cell:

• naïve T cells, which are T cells that have not yet been in contact with a foreign

antigen

• activated helper T cells, which are T cells that have been activated by a foreign

antigen.

Figure 5 shows electron microscope images of the two types of cell.

Figure 5

Naïve T cell Activated helper T cell

The activated helper T cell has a volume of 463 μm3

04.1 Calculate the volume of the naïve T cell shown in Figure 5.

Then calculate how many times larger the activated helper T cell volume is compared

with the naïve T cell volume.

Assume the cell is spherical.

Use line PQ to measure the diameter of the naïve T cell.

Volume of a sphere = πr3 where π is 3.14

Show your working.

[3 marks]

Volume of naïve T cell μm3

Number of times larger the activated helper T cell9

volume is compared with the naïve T cell volume

04.2 State one feature that shows the images in Figure 5 were taken with an electron

microscope and not an optical microscope.

Explain your answer.

[2 marks]

04.3 State one role of a helper T cell.

[1 mark]

04.4 The rate of translation is increased in T cells activated by antigens.

Describe the role of tRNA in translation.

[2 marks]

Mark scheme

Show the mark scheme Mark scheme showing accepted answers for parts 04.1 through 04.4, including volume calculations, electron microscope resolution and internal organelle visibility, helper T cell functions, and tRNA anticodon/amino acid binding roles.

Question Marking Guidance Mark Comments

58 = 2 marks

(Volume)

57.91 = 2 marks

Correct answer of 57.9 (μm ) = 2 marks;;

Accept 54.3/54 = 2

marks

OR Accept 61.6/62 = 2

marks

If volume incorrect, evidence of 2.35-2.45 (as

04.1 (3 x

radius) = 1 mark

AO2)

(Times larger) Allow 7.5 – 8.52

ECF Allow any

8 (times larger) (or ECF) = 1 mark; alternative for 8 which

shows 463 ÷ their

volume

1. Accept

1. Nuclear membrane /nucleolus /vesicles/

invaginations of

lysosomes/ribosomes distinct/visible;

membrane

distinct/visible

2. EM has greater resolution; (1 x

04.2 1. Reject nucleus

AO1, 1

1. Reject

x AO2)

mitochondrion

2. assume ‘it’ refers to

electron microscope

Stimulating cytotoxic T cells

OR

Accept ‘activate’ for

1 stimulating

04.3 Stimulating B cells

(AO1)

OR

Stimulating phagocytes;

1. Anticodon (on tRNA) binds to (complementary) 2

04.4 codon (on mRNA); – (2 xLOGY – – JUNE 2023

AO1)

2. (tRNA) brings/carries specific amino acid (to

ribosome); 9

How to answer it

Activation of T Lymphocytes Study Guide

What this question tests

This question assesses your ability to apply mathematical skills to biological structures (calculating spherical volumes and scaling factors), interpret microscope images to distinguish between electron and optical microscopes, recall the specific immunological role of helper T cells, and describe molecular protein synthesis mechanisms (translation and the role of tRNA).

Question 04.1 (3 Marks)

Calculating Cell Volume and Scaling Factors

✅ Correct Answers

  • Volume of naive T cell: 57.9 µm³ (Accept 57.91, 58, 54.3, or 61.6 depending on exact ruler measurements).
  • Number of times larger: 8 (Accept 7.5 to 8.5 , or any correct ECF value based on 463 ÷ your volume ).

📐 Step-by-Step Calculation

  1. Measure diameter: Use a ruler to measure line PQ on the naive T cell image in cm, then convert to µm using the scale bar ( 2 µm ). Let us assume a measured diameter d = 4.8 cm and scale bar 1.66 cm = 2 µm , giving an actual diameter of approx 4.8 µm (Accept range 4.7 to 4.9 µm ).
  2. Calculate radius (r): r = diameter ÷ 2 = approx 2.4 µm (Accept range 2.35 to 2.45 µm ). [1 mark for correct radius].
  3. Calculate volume: Use formula V = (4 ÷ 3) × π × r³ .
    V = (4 ÷ 3) × 3.14 × (2.4)³ = 57.9 µm³ . [2nd mark for volume].
  4. Calculate scaling factor: Divide activated helper T cell volume by naive T cell volume: 463 ÷ 57.9 = 8 . [3rd mark].

❌ Common Calculation Traps

  • Forgetting to halve the diameter: Using the full diameter instead of radius ( r ) in the r³ formula.
  • Incorrect scale bar conversion: Misreading the micrometer scale bar provided on the figure.
Mark breakdown: 2 marks for volume (1 mark for correct radius identification if final volume is wrong), 1 mark for the correct multiple/ECF.
Question 04.2 (2 Marks)

Microscopy Identification: Electron vs Optical

✅ Correct Answers

Any one valid structural feature visible, plus the correct explanation linking it to resolution:

  • Feature: Nuclear membrane, nucleolus, vesicles, lysosomes, or ribosomes are distinct/visible. (Reject nucleus or mitochondria alone as they can sometimes be vaguely seen with very high-end light microscopes).
  • Explanation: The electron microscope has a greater resolution (due to shorter wavelength of electrons).

💡 Key Knowledge

  • Optical microscopes use light waves with a long wavelength, limiting maximum resolution to ~0.2 µm.
  • Transmission Electron Microscopes (TEM) use electron beams with much shorter wavelengths, revealing internal ultrastructure like distinct nuclear envelopes and ribosomes.
Mark breakdown: 1 mark for identifying a valid organelle/feature visible only under TEM; 1 mark for stating electron microscopes have higher resolution.
Question 04.3 (1 Mark)

Role of a Helper T Cell

✅ Correct Answers

State one of the following target immune cells stimulated by helper T cells:

  • Stimulating cytotoxic T cells
  • Stimulating B cells (plasma cell pathway/antibody production)
  • Stimulating phagocytes

🧠 Exam Technique

Keep your answer concise and direct. Use precise immunological terminology—accept "activate" interchangeably with "stimulate". Avoid vague statements like "fights pathogens".

Mark breakdown: 1 mark for naming any correct cell type stimulated by helper T cells.
Question 04.4 (2 Marks)

Role of tRNA in Translation

✅ Correct Answers

  • 1. Anticodon on tRNA binds to the complementary codon on mRNA.
  • 2. tRNA brings/carries a specific amino acid to the ribosome.

❌ Common Errors

  • Confusing codons and anticodons: Stating that mRNA has anticodons or that tRNA has codons will lose you the first mark. Remember: mRNA = codon, tRNA = anticodon.
  • Vague amino acid reference: Saying "carries an amino acid" without specifying that it brings a specific amino acid coded by the triplet.
Mark breakdown: 2 marks total (1 mark for anticodon-codon complementary binding, 1 mark for bringing/transporting a specific amino acid).

Topics

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

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