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3.4.5
Species and Taxonomy
Analytical deep dive — question counts, mark distribution, mastery curves, command-word breakdowns, and examiner narrative analysis.
Questions
16
Total marks
28
Marks / Q
1.8
Accessibility
65.6%
Mastery
43.0%
Student strength
50.5%
01
At a glance
3.4.5 · Species and Taxonomy
8YRSYNTHESIS
3.4.5 (Species and Taxonomy) appeared in 8 of the 8 years between 2017 and 2024, contributing 16 questions and 28 marks across Papers 1, 2 and 3. APPLICATION dominates the mark distribution at 71.4% of total marks. The accessibility–mastery gap sits at 22.6 percentage points (65.6% vs 43.0%) — most students reach partial credit, but full marks remain harder to secure. Mastery varied year-to-year, lowest in 2022 (16.0%) and highest in 2018 (62.0%). Calculation marks are a small share (3.6%) but typically sit at the lower end of the mastery distribution.
Access–mastery gap
+23 pp
Lowest mastery
2022 · 16.0%
Highest mastery
2018 · 62.0%
02
Question type split
By marks · compound to dominant
28MARKS
28
marks
Application71.4%20 marks
Knowledge25.0%7 marks
Calculation3.6%1 marks
(by marks; compound rows assigned to dominant type):
03
Credit terms — quick reference
Mark scheme tier-locked
12TERMS
Tier 1 · Always credit
Tier 2 · Sometimes credit
common ancestorfertile offspring
Reject · Never credit
two answers given (no mark awarded)A. chlorogaster and A. piperi unrelated to P. pruinosano common ancestorno statistical testing (ignored)no sample size stated (ignored)magnification (unqualified)difficult to stain (without consequence)new technology (unqualified)evolved into new speciesmutated
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 | 4 | 7 | 60.0% | 48.5% |
| 2018 | 1 | 2 | 75.0% | 62.0% |
| 2019 | 1 | 2 | 65.0% | 25.0% |
| 2020 | 2 | 3 | — COVID | — COVID |
| 2021 | 1 | 1 | — COVID | — COVID |
| 2022 | 1 | 2 | 61.0% | 16.0% |
| 2023 | 3 | 5 | 65.0% | 35.0% |
| 2024 | 3 | 6 | 72.3% | 52.3% |
06
Mark scheme intelligence
2017–2024 mark scheme corpus
17TERMS
Tier 1 — frequently credited
| Term | Times credited | Years | Notes |
|---|---|---|---|
| common ancestor | 2 | 2017, 2018 | |
| fertile offspring | 2 | 2019, 2021 |
Tier 2 — sometimes credited
| Term | Times credited | Years | Notes |
|---|---|---|---|
| two answers given (no mark awarded) | 1 | 2017 | |
| A. chlorogaster and A. piperi unrelated to P. pruinosa | 1 | 2018 | |
| no common ancestor | 1 | 2018 | |
| no statistical testing (ignored) | 1 | 2022 | |
| no sample size stated (ignored) | 1 | 2022 | |
| magnification (unqualified) | 1 | 2023 | |
| difficult to stain (without consequence) | 1 | 2023 | |
| new technology (unqualified) | 1 | 2023 | |
| evolved into new species | 1 | 2023 | |
| mutated | 1 | 2023 | |
| magnification | 1 | 2023 | |
| 780 (sum of advertisement + rasping) | 1 | 2024 | |
| 2.5 (percentage used as count) | 1 | 2024 | |
| 1.5% or 0.5% | 1 | 2024 | |
| add males | 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
2CASE STUDIES
Conceptual errors
- Phylogenetic trees read backwards — in 2022, the most common error on a tree-reading question was concluding that more distant branch points indicated closer evolutionary relationship; the correct interpretation is that a more recent common ancestor (branch point closer to the tips) indicates greater relatedness; students who described two species as "unrelated" because their common ancestor appeared lower on the tree inverted the logic entirely (2022 P3 Q05.6)
- Reproductive isolation defined as producing infertile offspring without explaining the mechanism — in 2019, the definition of a species required reference to the ability to interbreed and produce fertile offspring; answers that mentioned "infertile offspring" without stating that this constitutes reproductive isolation — preventing gene flow — earned partial credit only; some students gave hybrid infertility as the definition of the species concept rather than as evidence for reproductive isolation (2019 P1 Q07.3)
- Magnification and resolution conflated — in 2023, students who suggested that higher magnification would reveal more detail about chromosomal features were penalised; magnification increases image size without improving the ability to distinguish fine structural detail; resolution is the relevant property for seeing small or closely spaced structures; this confusion appeared across multiple 2023 questions (2023 P1 Q06.2)
Vocabulary errors
- "Base" omitted from DNA sequencing descriptions — in 2023, descriptions of DNA sequencing that referred only to "sequencing the DNA" without specifying that base sequences are compared earned no mark at the precision point; AQA requires students to state that it is the base (nucleotide) sequence that is compared when using molecular evidence for classification (2023 P1 Q06.3)
- "Magnification" used instead of "resolution" when explaining microscopy limitations — as above, writing "magnification is not high enough" when resolution is the limiting factor demonstrates a conceptual error; the mark was for resolution, and substituting magnification showed misunderstanding of the property being discussed (2023 P1 Q06.2)
- "Evolved into new species" and "mutated" rejected as descriptions of phylogenetic divergence — these phrasings were explicitly listed as rejected in 2023; speciation requires reproductive isolation, not just mutation; stating that one species "evolved into" another implies linear succession rather than branching divergence (2023 P1 Q06.3)
Application errors
- Only 14% correct on molecular methods question — in 2017, a question asked which molecular technique would best provide evidence for evolutionary relationships; the majority of students described morphological comparison or behavioural evidence; the mark required naming a molecular approach (DNA base sequence comparison, amino acid sequence comparison, immunological comparisons) and most students' knowledge of molecular phylogeny was too thin to retrieve it under exam conditions (2017 P1 Q08.4)
- Two answers given where one was required — in 2017, a question with a single correct option was answered with two responses; when two answers are given, no mark is awarded regardless of whether one is correct; this was penalised at this sub-section and reflects poor exam technique rather than content ignorance (2017 P1 Q08.1)
- Percentage used as a count in calculation — in 2024, students used 2.5 (a percentage) directly as a count of individuals rather than converting it to the number of individuals it represented; percentage values and raw counts are not interchangeable in these calculations (2024 P1 Q09.1)
High-impact failures · examiner narrative
2017 P1 Q08.43 marks
Molecular evidence for classification. Only 14% scored all marks. The question required naming a molecular technique and explaining how it provides evidence for evolutionary relationships. Students who named morphological comparison, described behavioural similarities, or gave structural homologies earned zero — these are not molecular methods. DNA base sequencing and amino acid sequencing were the expected routes. The examiner noted that many students knew the concept of shared ancestry but could not name the molecular evidence types or explain why similar base sequences indicate recent common ancestry.
2022 P3 Q05.62 marks
Phylogenetic tree interpretation. Mastery 16.0% in 2022. The question asked which of two species was more closely related to a third, using a phylogenetic tree. The majority of students identified the wrong species, suggesting they read the tree direction incorrectly: the more distant branch point (further from the tips) was interpreted as more recent rather than more ancient. The examiner noted this as a consistent direction-reversal error rather than a content gap — students who understood common ancestry still misread which node was most recent.
08
Difficulty signals
Performance metric synthesis
23PP GAP
Mean accessibility
65.6%
Mean mastery
43.0%
Mean student strength
50.5%
The accessibility–mastery gap of 22.6 percentage points characterises this sub-section's difficulty profile. Most students reach partial credit; full marks remain harder to achieve. Within 3.4 (Genetic information, variation and relationships), 3.4.5 ranks 5 of 6 sub-sections by mean mastery (1 = hardest). Mastery trajectory is falling across the cohort window: 48.5% in 2017 → 52.3% in 2024 (+3.8 percentage points). Mean mastery was lowest in 2022 (16.0%) and highest in 2018 (62.0%).