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3.6.1
Stimuli and Responses
Analytical deep dive — question counts, mark distribution, mastery curves, command-word breakdowns, and examiner narrative analysis.
Questions
32
Total marks
72
Marks / Q
2.2
Accessibility
58.7%
Mastery
27.3%
Student strength
39.4%
01
At a glance
3.6.1 · Stimuli and Responses
8YRSYNTHESIS
3.6.1 (Stimuli and Responses) appeared in 7 of the 8 years between 2017 and 2024, contributing 32 questions and 72 marks across Papers 1, 2 and 3. APPLICATION dominates the mark distribution at 65.3% of total marks. The accessibility–mastery gap sits at 31.4 percentage points (58.7% vs 27.3%) — most students reach partial credit, but full marks remain harder to secure. The largest single question observed is worth 5 marks, signalling that AQA expects complete hierarchical accounts in this sub-section. Mastery varied year-to-year, lowest in 2018 (4.0%) and highest in 2022 (35.7%). Calculation marks are a small share (11.1%) but typically sit at the lower end of the mastery distribution.
Access–mastery gap
+31 pp
Lowest mastery
2018 · 4.0%
Highest mastery
2022 · 35.7%
02
Question type split
By marks · compound to dominant
72MARKS
72
marks
Application65.3%47 marks
Knowledge23.6%17 marks
Calculation11.1%8 marks
(by marks; compound rows assigned to dominant type):
03
Credit terms — quick reference
Mark scheme tier-locked
21TERMS
Tier 1 · Always credit
Tier 2 · Sometimes credit
action potentialretinal convergenceIAA/auxinconcentrationcell elongationtemperaturesignificantspatial summationthresholddepolarisationgenerator potential
Reject · Never credit
signals/messages (for impulses)green cones/blue cones/red cones (without 'sensitive'); green pigment/blue pigment/red pigment (without 'sensitive')contains/stores IAA (not sufficient — must say produces)produce energy (must say provide ATP); photosynthesis (glucose not for photosynthesis here)contamination (insufficient — does not explain mechanism); constant temperature alone (insufficient)'decreases length' on its own (must say decreases mean change in length)'there is no difference between observed and expected' (too general); stating a hypothesis rather than a null hypothesishumiditytype of coraldepth of water
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 | 0 | 0 | — COVID | — COVID |
| 2018 | 2 | 6 | 61.5% | 4.0% |
| 2019 | 9 | 17 | 57.2% | 30.4% |
| 2020 | 4 | 10 | — COVID | — COVID |
| 2021 | 5 | 15 | — COVID | — COVID |
| 2022 | 3 | 4 | 51.3% | 35.7% |
| 2023 | 5 | 10 | 61.6% | 32.6% |
| 2024 | 4 | 10 | 62.2% | 18.8% |
06
Mark scheme intelligence
2017–2024 mark scheme corpus
26TERMS
Tier 1 — frequently credited
| Term | Times credited | Years | Notes |
|---|---|---|---|
| action potential | 3 | 2020, 2023 | |
| retinal convergence | 2 | 2018, 2020 | |
| IAA/auxin | 2 | 2019, 2021 | |
| concentration | 2 | 2019 | |
| cell elongation | 2 | 2019, 2024 | |
| temperature | 2 | 2019, 2021 | |
| significant | 2 | 2019, 2021 | |
| spatial summation | 2 | 2020, 2023 | |
| threshold | 2 | 2020, 2023 | |
| depolarisation | 2 | 2020, 2023 | |
| generator potential | 2 | 2020, 2023 |
Tier 2 — sometimes credited
| Term | Times credited | Years | Notes |
|---|---|---|---|
| signals/messages (for impulses) | 3 | 2018, 2020 | |
| green cones/blue cones/red cones (without 'sensitive'); green pigment/blue pigment/red pigment (without 'sensitive') | 1 | 2018 | |
| contains/stores IAA (not sufficient — must say produces) | 1 | 2019 | |
| produce energy (must say provide ATP); photosynthesis (glucose not for photosynthesis here) | 1 | 2019 | |
| contamination (insufficient — does not explain mechanism); constant temperature alone (insufficient) | 1 | 2019 | |
| 'decreases length' on its own (must say decreases mean change in length) | 1 | 2019 | |
| 'there is no difference between observed and expected' (too general); stating a hypothesis rather than a null hypothesis | 1 | 2019 | |
| humidity | 1 | 2019 | |
| type of coral | 1 | 2019 | |
| depth of water | 1 | 2019 | |
| biotic factors from natural marine environment | 1 | 2019 | |
| 'results are significant' (must say 'movement/difference is significant'); p-values without comparison to 0.05 threshold | 1 | 2019 | |
| using 564 mm/min (moving away from light — wrong direction for upward daytime movement) | 1 | 2019 | |
| muscles constrict | 1 | 2020 | |
| reference to shaded/dark side; reference to away from light | 1 | 2021 |
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
3CASE STUDIES
Conceptual errors
- Trichromatic theory described using "green cones" rather than "green-sensitive cones" — less than 1% of students scored full marks on the 2018 trichromatic theory question; the specification requires distinguishing between cone types by their sensitivity to wavelengths, not by naming them as colour-specific structures; writing "red cones" or "blue pigments" implies the cones contain coloured pigment rather than differentially absorbing light, and was explicitly rejected (2018 P2 Q10.2)
- Colour perception described without explaining mixed stimulation — many students stated which cone types are stimulated by a given colour but did not explain that simultaneous stimulation of multiple cone types at different levels is what distinguishes colours from one another; stating that "red-sensitive cones detect red light" stops short of explaining how other colours, including yellow or orange, arise from mixed cone responses (2023 P2 Q05.1)
- Petri dish lids described as preventing contamination without explaining the mechanism — in 2019, only 3% of students scored both marks on the Petri dish lid question; the correct mechanism is that lids prevent evaporation of water from the IAA solutions, which would alter their concentration; "to prevent contamination" does not explain why contamination matters or what effect it would have on the variable being measured (2019 P2 Q03.3)
- IAA described as stored or contained in the shoot tip rather than produced there — in 2019, students who wrote "the tip contains IAA" were not credited; the specification requires students to state that the tip produces IAA; the distinction matters because removing the tip removes the source of production, not just a reservoir (2019 P2 Q03.1)
Vocabulary errors
- "Signals" or "messages" used instead of "impulses" — this error appeared across 2018 and 2023 and was among the most consistently penalised terminology failures in this sub-section; nerve impulses (action potentials) are electrochemical events with specific properties; "signals" and "messages" are colloquial terms that carry no biological precision and are explicitly rejected (2018 P2 Q10.1, 2023 P3 Q01.1)
- "Results are significant" written in statistical evaluation instead of "movement/difference is significant" — in 2019, the statistical evaluation mark required students to state that the movement of COTS (or the difference between conditions) was significant; "results are significant" is too broad and was rejected; significance applies to a specific comparison, not to the experiment as a whole (2019 P3 Q05.3)
- "Produce energy" used instead of "provide ATP" — in 2019, glucose metabolism described as "producing energy" was rejected; the correct statement is that glucose is respired to provide ATP; "energy" is not a product of respiration in the biological sense; ATP is the molecule that transfers chemical potential energy to cellular processes (2019 P2 Q03.2)
Application errors
- Trichromatic question answered by describing rod cells — in 2018, some students who knew about retinal cells described rod function rather than the trichromatic theory; the question specifically tested colour discrimination via cones, and discussing rods demonstrated misidentification of which cell type was relevant (2018 P2 Q10.2)
- Null hypothesis stated too broadly for the chi-squared COTS question — in 2019, students wrote "there is no difference between observed and expected" without specifying what behaviour and what light condition; the null hypothesis must reference the specific variables in the investigation — the type of light and the direction of COTS movement — to be credited (2019 P3 Q05.1)
- Speed calculation used wrong directional value — in 2019, approximately 12% of students scored the calculation correctly; a common error was using 564 mm/min (the speed at which COTS move away from a light source) rather than 259 mm/min (the speed at which they move towards it in constant daylight); selecting the wrong row from the data table produced a plausible but wrong answer (2019 P3 Q05.4)
High-impact failures · examiner narrative
2018 P2 Q10.23 marks
Trichromatic theory of colour vision. Less than 1% scored all three marks; only about a third scored any mark. The question was described as a new specification topic and students displayed a poor understanding of how different colours are perceived. The core error was naming cone types by colour rather than by spectral sensitivity: "green cones" instead of "green-sensitive cones" appeared in the majority of responses. Even when cone sensitivity was correctly described, students rarely explained that different colours result from the relative degree of stimulation across all three cone types simultaneously — this mechanism, required for the third mark, was almost universally absent.
2019 P2 Q03.32 marks3%full marks
Why Petri dish lids were used in IAA investigation. Only 3% scored both marks. The answer required explaining that lids prevent evaporation of water from IAA solutions, which would increase their concentration and invalidate the comparison between concentrations. Almost all students wrote "to prevent contamination" without any mechanistic explanation of why contamination would affect the IAA concentration or what variable it would confound. The examiner reported this as one of the least effective discriminators on the paper, with many students applying a generic laboratory safety response rather than thinking about the specific variable being controlled.
2023 P2 Q05.13 marks
Colour vision using trichromatic theory. Only 2.6% scored all three marks. Despite two-thirds of students scoring at least one mark for identifying the role of cones, this mark was frequently negated by writing "red cones" rather than "red-sensitive cones." The explanation of how other colours arise from differential stimulation of multiple cone types was almost never given; most students described what individual cone types do in isolation rather than how their combined response creates colour perception.
08
Difficulty signals
Performance metric synthesis
31PP GAP
Mean accessibility
58.7%
Mean mastery
27.3%
Mean student strength
39.4%
The accessibility–mastery gap of 31.4 percentage points characterises this sub-section's difficulty profile. Most students reach partial credit; full marks remain harder to achieve. Within 3.6 (Organisms respond to changes in their environments), 3.6.1 ranks 2 of 4 sub-sections by mean mastery (1 = hardest). Mastery trajectory is rising across the cohort window: 4.0% in 2018 → 18.8% in 2024 (+14.8 percentage points). Mean mastery was lowest in 2018 (4.0%) and highest in 2022 (35.7%).