Community Q&A
A-Level Biology May/June 2025 Q1(d)(ii): Student X stated that acid phosphatases and sorgoleone could be transported out of root…
A-Level Biology · Paper 9700/22 · May/June 2025 · Question 1(d)(ii) · [4 marks]
Student X stated that acid phosphatases and sorgoleone could be transported out of root hair cells using the same process. Student Y stated that acid phosphatases and sorgoleone are transported out of root hair cells using different processes. Suggest the reasons given by student X and by student Y to support their statements.
A full-marks model answer with a mark-by-mark examiner breakdown is below.
1 answer
- accepted ✓
Student X (Same Process)
Student X could reason that both substances are transported out of the cell via exocytosis. This is a form of bulk transport suitable for large molecules like the acid phosphatase enzyme. In this process, vesicles containing the substances, likely formed by the Golgi apparatus, move to the cell surface membrane. These vesicles then fuse with the cell surface membrane, releasing their contents into the surroundings.
Student Y (Different Processes)
Student Y could argue that the transport mechanisms differ due to the different chemical properties of the two molecules.
- Acid phosphatase: As an enzyme, it is a protein and therefore a large, hydrophilic molecule. It cannot pass through the lipid bilayer directly. It would be transported via facilitated diffusion through a specific transport protein embedded in the membrane.
- Sorgoleone: This molecule is hydrophobic/lipid-soluble. This property allows it to move directly across the hydrophobic core of the phospholipid bilayer by simple diffusion, down its concentration gradient.
How the marks are awarded
- B1 — For Student X: correctly identifies the shared process as exocytosis.
- B1 — For Student X: describes the mechanism of exocytosis, stating that vesicles move to and fuse with the cell surface membrane.
- B1 — For Student Y: explains that the enzyme (acid phosphatase) requires a transport or membrane protein to cross the membrane.
- B1 — For Student Y: explains that sorgoleone, being hydrophobic, can cross the phospholipid bilayer directly.
Common mistakes
- Confusing the properties of the molecules, for example, stating that the protein is hydrophobic or that sorgoleone is polar.
- Providing a vague mechanism like 'diffusion' without specifying 'simple' vs 'facilitated' and linking it to the properties of the specific molecule.
- Incorrectly suggesting active transport without any information about moving against a concentration gradient or using ATP.
- Only providing an explanation for one of the students (either X or Y) and therefore failing to access all the marks.
Examiner tip: Always link the chemical properties of a molecule, such as its size and polarity, to its specific mechanism of transport across a cell membrane.
AI-generated model answer, grounded in the official Cambridge mark scheme and reviewed by the MarkScheme team. Mark your own answer to this question →
Your answer
Sign in to answer this question.