Biological Molecules
Cross-subtopic analytical view — comparative performance, yearly shape, and aggregate question structure across all sub-sections.
3.1 (Biological molecules) spans 8 sub-sections contributing 87 questions and 243 marks across Papers 1, 2 and 3 in the 2017–2024 dataset. The topic contains 4 sub-sections with substantive data (≥5 questions) and 3 with sparse coverage (fewer than 5 questions). The heaviest sub-section by marks is 3.1.4 (Proteins and Enzymes, 124 marks); the lightest is 3.1.7 (Water, 5 marks — sparse coverage (1 question in dataset)). By mean mastery, 3.1.7 (Water) is the hardest sub-section at 20.0% (small sample — 1 question) and 3.1.3 (Lipids) is the easiest at 52.5%. The topic-level accessibility–mastery gap is 31.4 percentage points (69.4% vs 38.0%); partial credit is the norm here, but securing full marks requires the kind of precision most students don't consistently land.
| Subtopic | Title | Questions | Marks | Mean accessibility | Mean mastery | Gap (pp) |
|---|---|---|---|---|---|---|
| 3.1.1 | Monomers and Polymers | 2 | 8 | 75.0% | 25.5% | 49.5 |
| 3.1.2 | Carbohydrates | 13 | 37 | 75.4% | 45.4% | 30.0 |
| 3.1.3 | Lipids | 9 | 22 | 76.2% | 52.5% | 23.8 |
| 3.1.4 | Proteins and Enzymes | 44 | 124 | 66.4% | 35.4% | 31.0 |
| 3.1.5 | Nucleic Acids | 14 | 39 | 68.4% | 34.4% | 34.0 |
| 3.1.6 | ATP | 4 | 8 | 76.5% | 49.0% | 27.5 |
| 3.1.7 | Water | 1 | 5 | 65.0% | 20.0% | 45.0 |
| 3.1.8 | Inorganic Ions | 0 | 0 | — | — | — |
| Year | Total questions | Total marks |
|---|---|---|
| 2017 | 12 | 46 |
| 2018 | 13 | 33 |
| 2019 | 6 | 22 |
| 2020 | 9 | 20 |
| 2021 | 11 | 27 |
| 2022 | 11 | 29 |
| 2023 | 7 | 25 |
| 2024 | 12 | 26 |
The three most common command words across this topic are 'Describe', 'Suggest', 'Explain'. Two-mark questions account for 31% of questions (27 of 87), making them the modal question size. This topic includes 9 questions worth 5 or more marks, indicating that AQA expects extended hierarchical accounts in some sub-sections.
| Mark size | Count |
|---|---|
| 1 mark | 19 |
| 2 marks | 27 |
| 3 marks | 25 |
| 4 marks | 7 |
| 5+ marks | 9 |
The topic-level accessibility–mastery gap of 31.4 percentage points confirms a consistent partial-credit pattern — most students access the question but the full mark allocation proves harder to capture. Within this topic, 3.1.7 (Water) is the hardest sub-section at 20.0% mean mastery; 3.1.3 (Lipids) is the easiest at 52.5%. Topic-level mastery trajectory is broadly flat across the cohort window: 49.6% in 2017 → 43.3% in 2025 (-6.2 percentage points).