AQA AS Level Biology Paper 1, June 2025: Question 2

8 marks · Medium difficulty · Short Answer

Complete the diagram of an ATP molecule, describe ATP hydrolysis and the cellular use of phosphate, and describe the co-transport mechanism by which glucose is absorbed in the ileum.

Practise this question

Question

Question text

02.1 Figure 4 shows one component of an ATP molecule.

Figure 4

Complete Figure 4 to show the structure of an ATP molecule.

Label all of its components.

[2 marks]

02.2 Describe how phosphate is released from ATP within cells.

Explain one way in which this phosphate can be used by cells.

[3 marks]

How phosphate is released from ATP

One way in which phosphate can be used by cells

02.3 Cells lining the ileum of mammals absorb glucose against a concentration gradient.

Describe how.

[3 marks]

Mark scheme

Show the mark scheme

Question Marking Guidance Mark Comments

1. Adenine, ribose and 3 x phosphate correctly 1. Accept P in a

labelled; circle/P /PO –3

i 4

for phosphate. Reject

2. Bonds (between ribose and adenine and phosphorus

between ribose and phosphates) in correct 1. Ignore pentose,

positions; 2 reject deoxyribose

02.1 (2 x 1. Ignore labelling of

AO1) bonds

1. Ignore shapes of

adenine and

phosphates

1. Hydrolysis; 1. Reject hydrolysis of

hydrogen bond

2. ATP hydrolase;

1. Ignore other named

bonds

3. Phosphorylate other substances to make them

more reactive/change their shape

2. Accept ATPase

02.2 OR (3 x

3. Accept description

AO1)

of phosphorylation

To form DNA/RNA/phospholipids;

3. Accept any named

biological molecule

containing phosphate

e.g. triose phosphate

3. Ignore to form ATP

1. Sodium ions actively transported out (of cells); 1, 2 and 3. Accept

Na+ for sodium ions

2. Maintains/generates a concentration/diffusion 1. Accept ‘pumped

gradient (for sodium ions); 3 using ATP’ for active

02.3 (3 x transport

AO1) 1,2 and 3. Reject lack

of ‘ions’ once

3. Co-transport (with sodium ions); 3. Accept ‘co-

transporter’ for ‘co-

transport’

How to answer it

AQA AS Level Biology • Cell Biology & Biological Molecules

ATP Structure, Hydrolysis & Glucose Co-Transport

What This Question Tests

ATP Architecture: Identifying and drawing the three fundamental components of an adenosine triphosphate molecule and their attachments.
Hydrolysis Reaction & Enzymes: Precision regarding the chemical splitting of ATP by ATP hydrolase .
Biological Roles of Phosphate: Understanding phosphorylation (increasing reactivity/changing shape) or incorporation into biological polymers.
Secondary Active Transport: Step-by-step mechanism of glucose absorption in the ileum epithelial cells involving Na⁺/K⁺ pumps and co-transporter proteins.

Question 02.1: Drawing and Labelling the ATP Molecule

2 Marks • AO1 (Recall & Application)

✅ Required Diagram & Labels

Mark 1: Correctly label Ribose (the pentagon provided), Adenine (the nitrogenous base), and 3 × Phosphate groups.
Mark 2: Correct bond positions:
- Adenine attached directly to the ribose ring (to the left).
- Chain of 3 phosphate groups attached sequentially to the ribose ring (to the right).

💡 Diagram Visualisation

[Adenine] — [Ribose pentagon] — Ⓡ — Ⓡ — Ⓡ

Phosphates must be connected in a linear chain of 3. Labels can be full words or shorthand like P in a circle, Pi , or PO₄³⁻ .

🧠 Exam Technique

Label everything: The question asks you to "Label all of its components." Students frequently forget to label the pentagon itself as Ribose!
Shapes don't need to be artistic: The mark scheme specifically states: "Ignore shapes of adenine and phosphates". A rectangle for adenine and circles for phosphates earn full credit.

❌ Common Errors to Avoid

Writing Deoxyribose (instantly rejected; ATP contains ribose).
Writing Phosphorus instead of phosphate.
Branching the 3 phosphates off different carbon atoms on the ribose ring.

Mark Scheme Notes: Accept P in a circle, Pi , or PO₄³⁻ . Reject 'phosphorus'. Ignore 'pentose' (needs to be ribose for precision). Reject 'deoxyribose'.

Question 02.2: Phosphate Release and Cellular Utilisation

3 Marks • AO1 (Mechanism & Biological Context)

✅ Model Answer

How phosphate is released:

By a hydrolysis reaction (addition of water). [Mark 1]
Catalysed by the enzyme ATP hydrolase (or ATPase). [Mark 2]

One way used by cells (choose one):

To phosphorylate other substances/compounds, making them more reactive or changing their shape. [Mark 3]
OR To synthesise other biological molecules such as DNA, RNA, or phospholipids. [Mark 3]

💡 Chemical Equation

ATP + H₂O → ADP + Pi + Energy
Enzyme: ATP hydrolase

Phosphorylation adds a negative charge and phosphate group, frequently changing tertiary conformation of transport proteins or activating intermediates like glucose-6-phosphate in glycolysis.

❌ Common Pitfalls

"Hydrolysis of hydrogen bonds": Explicitly rejected! ATP cleavage breaks a covalent phosphoanhydride bond.
"Used to make ATP": Ignored by examiners. The question specifically asks what the released phosphate is used for in cellular work.
"Produces energy": ATP releases energy, it does not "produce" it (violates the law of conservation of energy).

🧠 Top Tip

Always name both the reaction type and the specific enzyme when asked how ATP is broken down. Writing just "broken down by water" loses the specific terminology mark for "hydrolysis".

Mark Scheme Notes: Mark 1: Hydrolysis. Mark 2: ATP hydrolase / ATPase. Mark 3: Phosphorylate other compounds to make more reactive / change shape OR formation of named phosphate-containing compound (DNA, RNA, phospholipids, triose phosphate).

Question 02.3: Glucose Absorption Against a Gradient

3 Marks • AO1 (Transport Across Membranes)

✅ 3-Step Marking Pathway

Active transport of sodium ions: Sodium ions (Na⁺) are actively transported out of the epithelial cell (into the capillary/blood) via the sodium-potassium pump. [Mark 1]
Concentration gradient established: This lowers the cellular Na⁺ concentration, creating/maintaining a concentration gradient for sodium ions (higher in lumen, lower inside the cell). [Mark 2]
Co-transport: Sodium ions and glucose enter the epithelial cell together from the lumen via co-transport (facilitated diffusion via a symport/co-transporter protein). [Mark 3]

🧠 Examiner Goldmine: The "Ion" Trap

The single most common reason students lose marks on this classic question:

⚠️ Examiner Comment: "Reject lack of 'ions' once."
If you write "sodium" instead of "sodium ions" or "Na⁺", you will immediately lose credit!

📐 Process Flow Summary

1. Basolateral Membrane: Active transport uses ATP to pump Na⁺ out into blood.
2. Cytoplasm: Intracellular [Na⁺] drops well below lumen [Na⁺].
3. Apical Membrane: Na⁺ flows down its concentration gradient through SGLT1 co-transporter, pulling glucose into the cell against its concentration gradient.
4. Basolateral Exit: Glucose exits into blood down its own gradient via facilitated diffusion (GLUT2).

❌ Common Errors

Stating glucose is directly actively transported by a single pump using ATP (glucose enters via secondary active transport / co-transport without directly hydrolysing ATP at the luminal membrane).
Failing to mention the concentration gradient of Na⁺.
Confusing the directions: sodium ions move out into the blood to pull sodium in from the gut lumen.

Mark Scheme Notes: Accept Na⁺ for sodium ions. Accept 'pumped using ATP' for active transport. Accept 'co-transporter' for 'co-transport'. Remember: Must specify ions.

Topics

Biology · 3.1 Biological molecules · 3.2 Cells · 3.3 Organisms exchange substances with their environment

Question and mark scheme from the AQA AS Level Biology examination, Paper 1, June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.