← Back to Intelligence
// TOPIC PROFILE
3.1.6
ATP
Analytical deep dive — question counts, mark distribution, mastery curves, command-word breakdowns, and examiner narrative analysis.
Questions
4
Total marks
8
Marks / Q
2.0
Accessibility
76.5%
Mastery
49.0%
Student strength
64.0%
01
At a glance
3.1.6 · ATP
8YRSYNTHESIS
3.1.6 (ATP) appeared in 4 of the 8 years between 2017 and 2024, contributing 4 questions and 8 marks across Papers 1, 2 and 3. KNOWLEDGE dominates the mark distribution at 100.0% of total marks. The accessibility–mastery gap sits at 27.5 percentage points (76.5% vs 49.0%) — most students reach partial credit, but full marks remain harder to secure. Mastery varied year-to-year, lowest in 2024 (25.0%) and highest in 2017 (73.0%).
Access–mastery gap
+28 pp
Lowest mastery
2024 · 25.0%
Highest mastery
2017 · 73.0%
02
Question type split
By marks · compound to dominant
8MARKS
8
marks
Knowledge100.0%8 marks
Application0.0%0 marks
Calculation0.0%0 marks
(by marks; compound rows assigned to dominant type):
03
Credit terms — quick reference
Mark scheme tier-locked
7TERMS
Tier 1 · Always credit
Tier 2 · Sometimes credit
ADPATP synthase
Reject · Never credit
formation of E-S complexpentose (spec requires ribose)adenine with 3 phosphates aloneglycosidic bonds in ATPhydrogen bonds
04
Question patterns
Recurring formats & tariff structure
0PARAGRAPHS
05
Year-over-year presence
P1 + P3 · 2017–2024
8YEARS
| Year | Questions | Total marks | Mean accessibility | Mean mastery |
|---|---|---|---|---|
| 2017 | 1 | 1 | 73.0% | 73.0% |
| 2018 | 0 | 0 | — COVID | — COVID |
| 2019 | 0 | 0 | — COVID | — COVID |
| 2020 | 1 | 2 | — COVID | — COVID |
| 2021 | 1 | 1 | — COVID | — COVID |
| 2022 | 0 | 0 | — COVID | — COVID |
| 2023 | 0 | 0 | — COVID | — COVID |
| 2024 | 1 | 4 | 80.0% | 25.0% |
06
Mark scheme intelligence
2017–2024 mark scheme corpus
7TERMS
Tier 1 — frequently credited
| Term | Times credited | Years | Notes |
|---|---|---|---|
| ADP | 2 | 2020, 2021 | |
| ATP synthase | 2 | 2021, 2024 |
Tier 2 — sometimes credited
| Term | Times credited | Years | Notes |
|---|---|---|---|
| formation of E-S complex | 1 | 2020 | |
| pentose (spec requires ribose) | 1 | 2024 | |
| adenine with 3 phosphates alone | 1 | 2024 | |
| glycosidic bonds in ATP | 1 | 2024 | |
| hydrogen bonds | 1 | 2024 |
Marks in this sub-section are typically awarded for precise terminology and correct application of biological principles. Sequential mark schemes — where each mark requires building on the previous one — are common in multi-mark questions; stating the first step without progression rarely earns more than one mark. Calculation marks are typically split between method (correct setup and value extraction) and answer (accurate numerical result), allowing partial credit when arithmetic errors occur.
07
Where students lose marks
Examiner-anchored error patterns
1CASE STUDIES
Conceptual errors
- ATP synthase and ATP hydrolase confused — the synthesis reaction (ADP + Pi → ATP + H₂O) selected as the hydrolysis reaction and vice versa; confusing which enzyme runs in which direction was the specific error flagged in 2017 Q05.1 (2017 P1 Q05.1)
- Hydrolysis and condensation reactions swapped — water described as produced in hydrolysis and used in condensation, when the reverse is true; the examiner noted this in 2024 Q10.3 as a confident inversion of a fundamental principle (2024 P1 Q10.3)
- ATP structure reduced to "ADP + Pi" — failing to describe the full three-phosphate structure with ribose and adenine; the mark scheme requires all three structural components to be named (2024 P1 Q10.3)
Vocabulary errors
- "Pentose" written instead of "ribose" for the sugar component of ATP — the specification identifies ribose by name; "pentose" is the class and was not credited (2024 P1 Q10.3)
- "Glycosidic bonds" or "hydrogen bonds" cited in ATP structure — neither applies; these errors transfer carbohydrate or protein terminology incorrectly into ATP chemistry (2024 P1 Q10.3)
- "Adenine" with three phosphates stated without mentioning ribose — the structural description must include ribose; adenine alone with phosphates omits the sugar component that connects the two (2024 P1 Q10.3)
Application errors
- "Hydrolysis" not stated for ATP hydrolase activity — students correctly described ATP → ADP + Pi but failed to name the reaction type; naming the reaction is a separate mark point requiring the process term, not just the molecular equation (2024 P1 Q10.3)
- Limited examiner data available for this category beyond the above.
High-impact failures · examiner narrative
2024 P1 Q10.34 marks25%full marks
Tested ATP structure and the reactions catalysed by ATP hydrolase and ATP synthase. Only 25% scored full marks, with most achieving 2–3. The structural mark was the most commonly missed: simple statements like "ATP is made of ADP and Pi" were not credited; ribose, adenine, and three phosphates must all be named. Ribose was the most frequently omitted component, and "pentose" was used as a substitute — not credited because the specification names ribose specifically. Glycosidic and hydrogen bonds appeared in multiple answers, indicating structural confusion with polysaccharides and proteins. The hydrolysis/condensation inversion was noted as a recurring error. Irrelevant metabolic content — ATP as an immediate energy source — appeared frequently and earned no marks.
08
Difficulty signals
Performance metric synthesis
28PP GAP
Mean accessibility
76.5%
Mean mastery
49.0%
Mean student strength
64.0%
The accessibility–mastery gap of 27.5 percentage points characterises this sub-section's difficulty profile. Most students reach partial credit; full marks remain harder to achieve. Within 3.1 (Biological molecules), 3.1.6 ranks 6 of 7 sub-sections by mean mastery (1 = hardest). Mean mastery was lowest in 2024 (25.0%) and highest in 2017 (73.0%).