AQA GCSE Biology Biology Paper 1 (Higher), June 2025: Question 7

✅ Model Answers

07.1: Stem cells can differentiate into any type of cell (or can differentiate into liver cells). 1 mark

07.2: Any one ethical reason: 1 mark

• Using an embryo destroys a (potential) human life.
• The embryo cannot give consent or make a choice.
• It goes against religious, cultural, or personal beliefs.

💡 Key Knowledge

Embryonic stem cells: Pluripotent cells derived from early-stage embryos. Unlike adult stem cells (e.g. from bone marrow, which can only form blood cells), embryonic stem cells can specialise into all cell types in the body.

🧠 Exam Technique

• Always use the scientific term differentiate rather than loose terms like "change into" or "grow into".
• For ethical questions, be clear and specific. Mentioning that the "embryo is destroyed" or "cannot consent" directly meets marking criteria.

❌ Common Errors

• Vague words like "specialisation" alone without explaining they can turn into any cell type.
• Writing simply "against religion" without specifying that it is against someone's faith/beliefs regarding the destruction of life.

✅ Model Answers

07.3: Cell Types in Figure 9 3 marks

• A: Lymphocyte (or spleen cell / B-cell) [1]
• B: Tumour cell (or myeloma cell) [1]
• C: Hybridoma cell [1]

07.4: How mouse is stimulated 1 mark

The mouse is injected with (liver) antigens (or injected with donor liver cells).

💡 Key Knowledge

To make monoclonal antibodies:

1. Inject mouse with target antigen.
2. Mouse B-lymphocytes produce antibodies but cannot divide.
3. Fuse lymphocyte with a tumour cell (which divides indefinitely) to create a hybridoma.
4. Clone the hybridoma to mass-produce identical (monoclonal) antibodies.

❌ Common Errors

• Writing "white blood cell" instead of lymphocyte for Cell A (rejected by mark scheme).
• Calling Cell B simply "cancer" rather than tumour cell or myeloma.
• In 07.4, stating the mouse is injected with a "pathogen" or "disease". The question specifies liver transplant rejection, so it is stimulated with liver antigens.

✅ Model Answers

07.5: Preventing attack by white blood cells 3 marks

1. Monoclonal antibodies bind to (liver) antigens / cells [1].
2. Because monoclonal antibodies are complementary in shape to the (liver) antigen [1].
3. So antibodies released by the patient's white blood cells cannot bind to the liver antigens (or phagocytes cannot detect/engulf the cells) [1].

07.6: One other use 1 mark

Any one from: Detect pathogens (e.g. lateral flow tests) / locate specific molecules in cells / deliver drugs or radioactive substances to cancer cells.

🧠 Exam Technique: "Explain how" (3 marks)

Notice the 3-step causal chain required for 07.5:

Binding → Reason (Complementary Shape) → Result (Blockade).

Always mention why they bind: their binding sites have a complementary shape to the specific antigens.

❌ Common Errors

• Saying antibodies have the "same shape" as antigens. They are complementary (fit together like lock and key).
• In 07.6, mentioning pregnancy tests when the question explicitly states: "Do not refer to pregnancy tests." Always read exclusions!
• Saying "to treat disease" without qualification. State how (e.g., deliver chemotherapy drugs to cancer cells).

📐 Part 07.8: Building a 6/6 Answer

To achieve Level 3 (5–6 marks), you must link two distinct pathways: Emulsification AND pH / Neutralisation, showing their direct effect on lipase.

Path 1: Emulsification (Surface Area)

1. Severe liver disease means less or no bile is produced.
2. Without bile, large lipid droplets are not emulsified into small droplets.
3. This means the surface area of the fat is not increased.
4. Therefore, lipase enzymes break down fats much more slowly.

Path 2: Neutralisation (Optimum pH)

1. Bile is alkaline and neutralises hydrochloric acid from the stomach.
2. With less bile, stomach acid is not properly neutralised.
3. The pH in the small intestine remains acidic and is not at the optimum pH for lipase.
4. Lipase enzymes can denature (active site changes shape) or work at a drastically lower rate.

🧠 Examiner Level Breakdown

• Level 3 (5–6 marks): Both pathways covered clearly. Specifically mentions lipase activity, emulsification, and pH/acid neutralisation.
• Level 2 (3–4 marks): Mentions both emulsification and neutralisation, but fails to fully link both to lipase activity.
• Level 1 (1–2 marks): Isolated facts (e.g. "bile is made in liver", "fats need lipase") with no logical sequence.