← Back to Intelligence
// TOPIC PROFILE
3.5.1
Photosynthesis
Analytical deep dive — question counts, mark distribution, mastery curves, command-word breakdowns, and examiner narrative analysis.
Questions
28
Total marks
64
Marks / Q
2.3
Accessibility
63.8%
Mastery
34.2%
Student strength
48.0%
01
At a glance
3.5.1 · Photosynthesis
8YRSYNTHESIS
3.5.1 (Photosynthesis) appeared in 8 of the 8 years between 2017 and 2024, contributing 28 questions and 64 marks across Papers 1, 2 and 3. KNOWLEDGE dominates the mark distribution at 50.0% of total marks. The accessibility–mastery gap sits at 29.7 percentage points (63.8% vs 34.2%) — most students reach partial credit, but full marks remain harder to secure. The largest single question observed is worth 6 marks, signalling that AQA expects complete hierarchical accounts in this sub-section. Mastery varied year-to-year, lowest in 2022 (13.8%) and highest in 2024 (44.3%). Calculation marks are a small share (6.2%) but typically sit at the lower end of the mastery distribution.
Access–mastery gap
+30 pp
Lowest mastery
2022 · 13.8%
Highest mastery
2024 · 44.3%
02
Question type split
By marks · compound to dominant
64MARKS
64
marks
Knowledge50.0%32 marks
Application43.8%28 marks
Calculation6.2%4 marks
(by marks; compound rows assigned to dominant type):
03
Credit terms — quick reference
Mark scheme tier-locked
26TERMS
Tier 1 · Always credit
reduced NADPATPGPlight-dependent reactionNADPHCalvin cycleRuBPtriose phosphaterubisco
Tier 2 · Sometimes credit
chloroplastDCPIPreductionTPlight-independent reactionwatersolvent front
Reject · Never credit
reduced NADcell bursts/shrivels (must specify chloroplast)turgidflaccidprotonshydrogen ionsH+ aloneoxidation of DCPIPNADHglucose phosphate (for GP)
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 | 5 | 9 | 63.2% | 35.0% |
| 2018 | 4 | 9 | 72.2% | 38.5% |
| 2019 | 6 | 8 | 54.0% | 43.0% |
| 2020 | 1 | 2 | — COVID | — COVID |
| 2021 | 2 | 6 | — COVID | — COVID |
| 2022 | 5 | 17 | 53.0% | 13.8% |
| 2023 | 2 | 6 | 68.0% | 32.5% |
| 2024 | 3 | 7 | 88.7% | 44.3% |
06
Mark scheme intelligence
2017–2024 mark scheme corpus
31TERMS
Tier 1 — frequently credited
| Term | Times credited | Years | Notes |
|---|---|---|---|
| reduced NADP | 6 | 2017, 2018, 2020, 2022, 2024 | |
| ATP | 5 | 2017, 2018, 2020, 2022, 2024 | |
| GP | 5 | 2017, 2018, 2021, 2022, 2024 | |
| light-dependent reaction | 4 | 2017, 2018, 2019 | |
| NADPH | 4 | 2017, 2020, 2022, 2024 | |
| Calvin cycle | 4 | 2017, 2021, 2022 | |
| RuBP | 4 | 2018, 2021, 2022 | |
| triose phosphate | 4 | 2021, 2022, 2024 | |
| rubisco | 3 | 2018, 2021, 2022 |
Tier 2 — sometimes credited
| Term | Times credited | Years | Notes |
|---|---|---|---|
| chloroplast | 2 | 2017, 2018 | |
| DCPIP | 2 | 2017 | |
| reduction | 2 | 2017, 2024 | |
| TP | 2 | 2017, 2024 | |
| light-independent reaction | 2 | 2018 | |
| water | 2 | 2019, 2024 | |
| solvent front | 2 | 2019, 2023 |
Commonly rejected language
| Term | Times rejected | Years | Why rejected |
|---|---|---|---|
| reduced NAD | 3 | 2018, 2020, 2024 | |
| cell bursts/shrivels (must specify chloroplast) | 1 | 2017 | |
| turgid | 1 | 2017 | |
| flaccid | 1 | 2017 | |
| protons | 1 | 2017 | |
| hydrogen ions | 1 | 2017 | |
| H+ alone | 1 | 2017 | |
| oxidation of DCPIP | 1 | 2017 | |
| NADH | 1 | 2018 | |
| glucose phosphate (for GP) | 1 | 2018 | |
| stoma | 1 | 2018 | |
| cytoplasm | 1 | 2018 | |
| mitochondrion | 1 | 2018 | |
| reduced NADP (that is an output); ATP (product not reactant); oxygen (product of photolysis); carbon dioxide (Calvin cycle | 1 | 2019 | |
| not LDR) | 1 | 2019 |
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
4CASE STUDIES
Conceptual errors
- Calvin cycle confused with Krebs cycle — in 2018, a question on the light-independent reactions saw a significant proportion of students describe the Krebs cycle instead of the Calvin cycle; both cycles involve carbon compounds and coenzymes but in entirely different organelles and metabolic contexts; the mark required naming the Calvin cycle and identifying GP, RuBP, and triose phosphate as its intermediates (2018 P2 Q01.2)
- Reduced NAD written instead of reduced NADP in photosynthesis — reduced NAD (NADH) is the coenzyme produced in respiration and the Krebs cycle; photosynthesis produces reduced NADP (NADPH) during the light-dependent reactions; substituting one for the other was explicitly rejected across 2018, 2020, and 2024 and was among the most consistently penalised errors in this sub-section (2018 P2 Q01.2, 2024 P2 Q03.3)
- Light-dependent reaction and light-independent reaction products confused — in 2019, students listed reduced NADP, ATP, and oxygen as inputs to the Calvin cycle rather than as outputs of the light-dependent stage; some listed carbon dioxide as a product of the light-dependent reactions; the mark scheme required products and inputs to be correctly assigned to the correct stage (2019 P2 Q07.1)
Vocabulary errors
- "TP" abbreviation rejected — in 2022, triose phosphate abbreviated as "TP" was explicitly not credited; the abbreviation is not in the specification; the full term "triose phosphate" is required; only 1.68% of students scored all marks on the 2022 Calvin cycle question, and the abbreviation rejection was a contributing factor (2022 P3 Q05.3)
- "Glucose phosphate" written instead of "GP" (glycerate-3-phosphate) — in 2018, students who named a glucose phosphate compound when asked for the three-carbon intermediate of the Calvin cycle lost the mark; GP is a specific three-carbon acid, not a glucose derivative; the chemical identity matters and glucose phosphate is a different compound (2018 P2 Q01.2)
- Control tube described as "a control" without identifying what it controls — in 2017, fewer than 10% scored the mark for explaining the role of a control tube in a chromatography or DCPIP experiment; "because it's a control" restates the label without explaining that it holds all variables constant except the one being tested, providing a baseline for comparison (2017 P2 Q04.2)
Application errors
- Light-dependent reaction described instead of Calvin cycle when specifically asked about the light-independent stage — in 2017, approximately 50% of students scored zero on a question about the Calvin cycle because they wrote about photolysis, ATP synthesis, and NADPH production in the light-dependent reactions; when a question specifies the light-independent stage, the answer must be confined to that stage (2017 P2 Q04.5)
- Pencil line placed in wrong position on chromatogram — in 2019, only 20% correctly placed the origin line at the base rather than at the solvent front; the sample is spotted and the pencil baseline drawn at the bottom of the paper before the solvent runs upward; many students drew the line at the top, reversing the direction of the technique (2019 P2 Q07.3)
- Chromatography separation attributed to polarity without identifying solubility in the solvent — in 2023, 61% scored zero on a question about why pigments separate on a chromatogram; the mark required that different pigments have different solubilities in the solvent; stating "different polarities" or "different properties" without specifying solubility was insufficient; the mechanism is differential solubility, not polarity in isolation (2023 P2 Q01.2)
High-impact failures · examiner narrative
2017 P2 Q04.52 marks
Role of the light-independent reaction in producing organic molecules. Approximately 50% scored zero. The question required students to describe the Calvin cycle: CO₂ combines with RuBP using rubisco to form GP; GP is reduced using ATP and reduced NADP to form triose phosphate; RuBP is regenerated. Students who described photolysis, photophosphorylation, or ATP synthesis scored nothing. The examiner noted this was a reliable discriminator: students who could reproduce the Calvin cycle accurately scored both marks, and those who could not fell back on the more familiar light-dependent content.
2022 P3 Q05.33 marks
Calvin cycle detail. Only 1.68% scored all three marks — among the lowest mark rates recorded across the data window. The question required naming specific intermediates (RuBP, GP, triose phosphate), their relationships, and the roles of ATP and reduced NADP. The "TP" abbreviation rejection cost many students a mark. Students who knew the cycle sequence but described it at the level of "carbon dioxide is fixed and glucose is produced" without intermediates scored zero. The examiners identified this as a question where students could not distinguish between knowing the cycle exists and knowing how it works step by step.
2023 P2 Q01.22 marks
Why photosynthetic pigments separate during chromatography. 61% scored zero. The question required students to state that different pigments have different solubilities in the solvent and that more soluble pigments travel further. The dominant wrong answers attributed separation to "different-sized molecules," "different molecular masses," or "different polarities" — all of which describe related properties but do not identify solubility as the operative mechanism. The examiner noted that students who had performed chromatography as a practical often described what they observed without understanding the principle behind the separation.
2024 P2 Q03.32 marks
Products of the light-dependent reactions used in the Calvin cycle. The marks required reduced NADP and ATP as inputs from the light-dependent stage. Reduced NAD was accepted zero times — it is the respiration coenzyme. Despite this being the most consistently rejected substitution across multiple years, it appeared repeatedly in 2024 answers. Students who wrote NADH or reduced NAD in a photosynthesis context demonstrated a fundamental coenzyme confusion that cascaded across both marks.
08
Difficulty signals
Performance metric synthesis
30PP GAP
Mean accessibility
63.8%
Mean mastery
34.2%
Mean student strength
48.0%
The accessibility–mastery gap of 29.7 percentage points characterises this sub-section's difficulty profile. Most students reach partial credit; full marks remain harder to achieve. Within 3.5 (Energy transfers in and between organisms), 3.5.1 ranks 4 of 4 sub-sections by mean mastery (1 = hardest). Mastery trajectory is broadly flat across the cohort window: 35.0% in 2017 → 44.3% in 2024 (+9.3 percentage points). Mean mastery was lowest in 2022 (13.8%) and highest in 2024 (44.3%).