AQA AS Level Biology Paper 2, June 2023: Question 2

6 marks · Medium difficulty · Short Answer

Complete a passage about ATP synthase structure, reaction type, and cellular process, and explain how its shape allows it to catalyse ATP synthesis and allow hydrogen ion movement.

Practise this question

Question

Figure 1 shows an ATP synthase enzyme embedded in the inner mitochondrial membrane, with H+ ions passing through it and catalysing the conversion of ADP + Pi into ATP. Below Figure 1, question 02.1 asks students to fill in missing terms in a passage about the structure of ATP synthase, reaction type, and respiration. Question 02.2 asks students to suggest and explain how the shape of ATP synthase allows it to synthesise ATP and allow movement of H+ ions.
Question text

02.1 Figure 1 shows an ATP synthase enzyme in the inner mitochondrial membrane.

Figure 1

Complete the passage with the appropriate terms.

[2 marks]

ATP synthase comprises several polypeptides, so is said to have

a structure.

It catalyses the synthesis of an ATP molecule by a

reaction; this involves the of a water molecule.

The ATP synthase in Figure 1 is in a mitochondrion so would catalyse reactions

during .

02.2 As shown in Figure 1, ATP synthase has two functions.

• It catalyses the synthesis of ATP.

• It allows the movement of H+ ions.

Suggest how the shape of the ATP synthase allows it to have these two functions.

Explain your answers.

[4 marks]

Catalyses the synthesis of ATP

Allows the movement of H+ ions

Mark scheme

Show the mark scheme The mark scheme provides answers for question 02.1 (quaternary, condensation/phosphorylation/reductive, release/loss/formation, (aerobic) respiration) and question 02.2 for synthesising ATP (active site complementary to ADP + Pi, enzyme-substrate complex forms) and allowing H+ movement (channel protein, facilitates diffusion of H+ or specific tertiary structure for H+).

Question Marking Guidance Mark Comments

Quaternary

Condensation/phosphorylation/redox

Release/loss/formation Accept ‘elimination’,

2 ‘production’ for

(Aerobic) respiration;; release

02.1 (2 x

AO1)

All correct = 2 marks,

2–3 correct = 1 mark,

0–1 correct = 0 marks

(Catalyses the synthesis of ATP)

1. Active site complementary to ADP + Pi;

2. Enzyme-substrate complex forms; 2. ‘E-S’ alone is

insufficient

(Allows the movement of H+ ions) 4

02.2 (4 x Accept ‘pore’

3. Channel (in membrane/protein/enzyme);

+ AO2)

4. Allows facilitated diffusion of H

OR

(Channel) has tertiary structure specific for (only)

H+

;

How to answer it

ATP Synthase Structure & Function Study Guide

What this question tests

This question assesses your understanding of protein structure (specifically quaternary structure), enzyme-catalysed reactions (condensation/phosphorylation), and how the specialized 3D tertiary structure of membrane proteins allows them to function simultaneously as enzymes and transmembrane channels during aerobic respiration.

Question 02.1

Complete the passage with appropriate terms (2 marks)

✅ Correct Answers

  • 1st gap: Quaternary
  • 2nd gap: Condensation (accept phosphorylation / redox)
  • 3rd gap: Release (accept elimination / production / loss / formation)
  • 4th gap: (Aerobic) respiration

💡 Key Knowledge

  • Proteins made of more than one polypeptide chain possess a quaternary structure.
  • Joining ADP and Pi to form ATP involves a condensation reaction where a water molecule is eliminated/released.
  • ATP synthase is located in the inner mitochondrial membrane, functioning during oxidative phosphorylation in aerobic respiration.

🧠 Exam Technique

  • Mark allocation: All 4 correct = 2 marks; 2 to 3 correct = 1 mark; 0 to 1 correct = 0 marks.
  • Ensure you use precise biological terminology—do not confuse condensation with hydrolysis.

❌ Common Errors

  • Writing "tertiary" instead of quaternary for proteins containing multiple polypeptides.
  • Stating "hydrolysis" instead of condensation because ATP breakdown is more commonly memorized.
Mark scheme breakdown: 2 marks total (2 × AO1)

Question 02.2

Suggest how the shape of ATP synthase allows it to have two functions (4 marks)

✅ Correct Answers

  • Point 1: Active site is complementary to ADP + Pi.
  • Point 2: Enzyme-substrate complex forms.
  • Point 3: Acts as a channel (in membrane/protein/enzyme) / pore for H⁺ ions.
  • Point 4: Allows facilitated diffusion of H⁺ OR has a tertiary structure specific for (only) H⁺.

💡 Key Knowledge

  • Dual-function proteins combine enzymatic catalytic sites with hydrophilic aqueous channels.
  • Movement of protons (H⁺) down an electrochemical gradient through a channel protein occurs via facilitated diffusion.

🧠 Exam Technique

  • Split your answer clearly into the two functions requested by the prompt: catalytic synthesis versus ion movement.
  • Use the phrase complementary when discussing active sites and substrates.

❌ Common Errors

  • Just writing "E-S" without expanding to "enzyme-substrate complex forms" (insufficient for mark 2).
  • Failing to link the channel property to its specific 3D tertiary structure or to facilitated diffusion.
Mark scheme breakdown: 4 marks total (4 × AO2 - application of knowledge)

Topics

Biology · 3.1 Biological molecules · 3.2 Cells

Question and mark scheme from the AQA AS Level Biology examination, Paper 2, June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.