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

10 marks · Medium difficulty · Extended Answer

Identify eukaryotic cell organelles and their roles in enzyme secretion, interpret a graph comparing glucose uptake mechanisms with and without oxygen, and calculate an uptake ratio.

Practise this question

Question

Question 02 includes a diagram of part of a eukaryotic cell (Figure 3) with labels X pointing to a mitochondrion, Y to the rough endoplasmic reticulum, and Z to the Golgi apparatus. Sub-questions ask to name X and its function (2 marks), explain why pancreatic cells contain large numbers of Y and Z to secrete digestive enzymes (4 marks), and analyze a line graph (Figure 4) showing rate of glucose uptake against external glucose concentration. Figure 4 features Curve S (with oxygen) which rises steeply from 0 to plateau at 600 arbitrary units, and Curve T (without oxygen) which remains at zero until approximately 6 mg dm⁻³ and then increases linearly to 240 arbitrary units at 14 mg dm⁻³. Questions ask for conclusions about glucose uptake mechanisms (3 marks) and to calculate the uptake ratio with oxygen : without oxygen at 14 mg dm⁻³ (1 mark).
Question text

02 Figure 3 shows part of a eukaryotic cell.

Figure 3

02.1 Name the organelle labelled X and state its function.

[2 marks]

Name

Function

02.2 Pancreatic cells produce and secrete digestive enzymes.

Explain why pancreatic cells contain large numbers of organelles Y and Z.

[4 marks]

02.3 A scientist placed pancreatic cells in solutions containing different concentrations of

glucose. The scientist measured the rate of uptake of glucose by these cells.

Figure 4 shows the scientist's results.

Figure 4

Using Figure 4, what can you conclude about the processes involved in the uptake of

glucose molecules by pancreatic cells?

[3 marks]

02.4 Use Figure 4 to calculate the ratio

rate of glucose uptake with oxygen : rate of glucose uptake with no oxygen

at an external glucose concentration of 14 mg dm–3

[1 mark]

Ratio =

Mark scheme

Show the mark scheme Mark scheme for Question 02: 02.1 awards 1 mark for Mitochondrion and 1 mark for Aerobic respiration (rejects produces/makes energy). 02.2 awards 4 marks for: enzymes are proteins; Y/RER produces proteins/enzymes; Z/Golgi apparatus modifies/packages proteins/enzymes; vesicles transport proteins/enzymes to cell-surface membrane. 02.3 awards up to 3 marks for: Curve S/with oxygen involves active transport/uses ATP; Curve S levels off when carrier proteins are saturated; Curve T/without oxygen involves facilitated diffusion/channel/carrier proteins; uptake in curve T begins when external glucose concentration exceeds internal concentration. 02.4 awards 1 mark for the ratio 2.5 : 1.

Question Marking Guidance Mark Comments

2. Reject

1. Mitochondrion; 2

produces/makes

02.1 (2 x energy

2. Aerobic respiration; AO1)

1. (Digestive) enzymes are proteins;

2. Ignore RER/ER

2. Y/rough endoplasmic reticulum produces

2. Accept ribosomes

proteins/enzymes;

4 3. Accept Golgi

3. Z/Golgi apparatus modifies/packages

02.2 (4 x body/complex

proteins/enzymes;

AO2)

4. (Golgi) vesicles

4. (Golgi) vesicles transport (modified)

transport (modified)

proteins/enzymes to (cell-surface) membrane;

proteins/enzymes for

exocytosis;

1. Curve S/with oxygen active transport of glucose 1. Accept co-transport

occurs for active transport

OR

Curve S/with oxygen the cells to use ATP to take

up glucose;

2. Curve S levels off when all carrier proteins are in

use;

3. Curve T/without oxygen facilitated diffusion

occurs

3 max

02.3 OR (3 x

AO3)

Curve T/without oxygen movement through

channel/carrier proteins

OR

At 6 mg dm-3 facilitated diffusion;

4. Uptake in curve T/without oxygen starts when

glucose concentration outside cells is greater

(than inside cells);

6 Question Marking Guidance Mark Comments

2.5 : 1; 1

02.4 (1 x

AO2)

How to answer it

Organelle Functions & Glucose Transport in Pancreatic Cells

📌 What this question tests

This question assesses knowledge across two fundamental AS-Level specification topics: Eukaryotic Cell Structure (3.2.1.1) and Transport across Cell Membranes (3.2.3).

  • Organelle Identification & Function: Recognising mitochondria, rough endoplasmic reticulum (RER), and the Golgi apparatus from cell diagrams, and linking their roles to protein/enzyme secretion.
  • Data Analysis & Deduction: Comparing rates of solute uptake with and without oxygen to deduce mechanisms of transport (active transport vs. facilitated diffusion).
  • Mathematical Skills: Reading values accurately from multi-line coordinate graphs and expressing relationships as simplified ratios ( n : 1 ).
Question 02.1 • 2 Marks

Organelle X Identification and Function

Identifying organelle X from Figure 3 and stating its biological role

✅ Correct Answer

  • Name: Mitochondrion (plural: mitochondria is accepted)
  • Function: Aerobic respiration (or produces ATP via aerobic respiration)

❌ Common Errors & Misconceptions

  • "Produces / makes energy": Strongly rejected by examiners! Energy cannot be created or destroyed; it is transferred in the form of ATP.
  • "Respiration" alone: Stating just "respiration" often loses the mark at A-Level. You must specify aerobic respiration, as anaerobic respiration occurs in the cytoplasm.
Mark Scheme Breakdown: 1 mark for naming Mitochondrion ; 1 mark for stating Aerobic respiration .
Question 02.2 • 4 Marks

Roles of Organelles Y and Z in Enzyme Secretion

Explaining the abundance of Rough Endoplasmic Reticulum and Golgi apparatus in pancreatic cells

✅ Correct Answer (4 Key Steps)

  1. (Digestive) enzymes are proteins.
  2. Organelle Y (Rough Endoplasmic Reticulum / Ribosomes): synthesises / produces proteins/enzymes.
  3. Organelle Z (Golgi apparatus): modifies and packages proteins/enzymes.
  4. (Golgi) vesicles: transport proteins/enzymes to the cell-surface membrane (for exocytosis / secretion).

💡 Key Knowledge

  • Organelle Y: Rough Endoplasmic Reticulum (RER), identified by folded cisternae studded with ribosomes.
  • Organelle Z: Golgi apparatus / body, identified by flattened, curved stacks of membrane (cisternae) without ribosomes, forming budding vesicles at its edges.
  • Pancreatic acinar cells are specialised secretory cells designed to release large quantities of digestive enzymes into ducts.

🧠 Exam Technique

Always state the fundamental nature of the product first: "Enzymes are proteins." This simple opening statement earns Mark Point 1. Then, describe the pathway logically from synthesis → modification/packaging → transport/exocytosis.

❌ Common Errors

  • Failing to identify that Y is RER and Z is Golgi apparatus before describing their functions.
  • Writing just "ER" without specifying rough ER (the mark scheme notes: ignore RER/ER as an isolated organelle name, but awards the mark for describing protein synthesis at RER/ribosomes).
  • Forgetting to mention the role of vesicles in transport to the plasma membrane.
Mark Scheme Breakdown: 4 marks available (AO2). 1 mark per bullet point: protein nature → RER role → Golgi role → vesicle transport role.
Question 02.3 • 3 Marks

Deducing Glucose Uptake Mechanisms from Figure 4

Interpreting rate curves with oxygen (Curve S) and without oxygen (Curve T)

✅ Mark Scheme Deductions (Any 3 of the following)

  • Active transport: Curve S / presence of oxygen allows active transport of glucose (or cells use ATP to take up glucose / co-transport).
  • Carrier saturation: Curve S levels off because carrier/transport proteins become saturated (all in use / limiting factor).
  • Facilitated diffusion: Curve T / absence of oxygen involves facilitated diffusion (movement through channel/carrier proteins without ATP).
  • Concentration threshold: Uptake in curve T only begins at 6 mg dm⁻³ / when external glucose concentration exceeds internal glucose concentration.

🧠 Top-Level Examiner Insight

  • With Oxygen (Curve S): Oxygen enables aerobic respiration → produces ATP → powers active transport against or up a concentration gradient. Uptake starts even at 0 external concentration.
  • Why Curve S plateaus: The rate reaches a Vmax because carrier proteins are saturated, not because glucose runs out!
  • Without Oxygen (Curve T): No aerobic ATP → active transport stops. Uptake is zero until 6 mg dm⁻³; this reveals that internal glucose is 6 mg dm⁻³, so passive facilitated diffusion can only occur down a gradient once external concentration > 6 mg dm⁻³.
Mark Scheme Breakdown: 3 max marks (AO3). Requires linking specific curves to active transport (requiring ATP), protein saturation, and facilitated diffusion driven by a concentration gradient.
Question 02.4 • 1 Mark

Ratio Calculation

Calculate the ratio of uptake rate with oxygen : without oxygen at 14 mg dm⁻³

📐 Step-by-Step Calculation

  1. Step 1: Read Curve S (with oxygen) at 14 mg dm⁻³:
    Find 14 on the x-axis, read up to Curve S (solid line) → 600 arbitrary units.
  2. Step 2: Read Curve T (without oxygen) at 14 mg dm⁻³:
    Find 14 on the x-axis, read up to Curve T (dashed line) → exactly two small grid squares below 250 = 240 arbitrary units (each small square on y-axis = 10 units).
  3. Step 3: Set up the ratio in the requested order:
    Rate with oxygen : Rate without oxygen = 600 : 240
  4. Step 4: Simplify to the standard n : 1 format:
    Divide both sides by 240:
    600 ÷ 240 = 2.5
    240 ÷ 240 = 1
    Final Ratio = 2.5 : 1

❌ Common Errors & Pitfalls

  • Reversing the terms: Writing 1 : 2.5 (or 0.4 : 1) loses the mark because the question asked for with oxygen : without oxygen.
  • Misreading the y-axis scale: 1 large square = 100 units (divided into 10 small squares), meaning 1 small square = 10 units. Curve T crosses 14 mg dm⁻³ at 240, not 250 or 230.
  • Leaving unsimplified: While sometimes allowed, AQA mark schemes strictly prefer simplified integer or decimal ratios (e.g. 2.5 : 1 or 5 : 2 ).
Mark Scheme Breakdown: 1 mark for 2.5 : 1 (or equivalent simplified ratio such as 5 : 2).

Topics

Biology · Practical skills · 3.2 Cells · Data analysis

Question and mark scheme from the AQA AS Level Biology examination, Paper 2, June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.