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3.4.6
Biodiversity within a Community
Analytical deep dive — question counts, mark distribution, mastery curves, command-word breakdowns, and examiner narrative analysis.
Questions
23
Total marks
51
Marks / Q
2.2
Accessibility
63.5%
Mastery
31.6%
Student strength
49.0%
01
At a glance
3.4.6 · Biodiversity within a Community
8YRSYNTHESIS
3.4.6 (Biodiversity within a Community) appeared in 7 of the 8 years between 2017 and 2024, contributing 23 questions and 51 marks across Papers 1, 2 and 3. APPLICATION dominates the mark distribution at 58.8% of total marks. The accessibility–mastery gap sits at 31.8 percentage points (63.5% vs 31.6%) — 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 2023 (16.0%) and highest in 2019 (41.2%). Calculation marks are a small share (9.8%) but typically sit at the lower end of the mastery distribution.
Access–mastery gap
+32 pp
Lowest mastery
2023 · 16.0%
Highest mastery
2019 · 41.2%
02
Question type split
By marks · compound to dominant
51MARKS
51
marks
Application58.8%30 marks
Knowledge31.4%16 marks
Calculation9.8%5 marks
(by marks; compound rows assigned to dominant type):
03
Credit terms — quick reference
Mark scheme tier-locked
16TERMS
Tier 1 · Always credit
index of diversityspecies richnessrepresentativenumber of species
Tier 2 · Sometimes credit
random samplingno correlation
Reject · Never credit
inappropriate sampling (quadrats/random coordinates in field)unqualified results being significantN = number of speciespercentage covercounting individualsnumber of each speciesresults are due to chanceresults are not due to chanceP (unqualified)in a population
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 | 13 | 68.0% | 29.5% |
| 2018 | 4 | 9 | 60.8% | 29.2% |
| 2019 | 4 | 6 | 63.0% | 41.2% |
| 2020 | 1 | 2 | — COVID | — COVID |
| 2021 | 0 | 0 | — COVID | — COVID |
| 2022 | 3 | 5 | 66.7% | 38.3% |
| 2023 | 3 | 7 | 54.0% | 16.0% |
| 2024 | 4 | 9 | 66.8% | 33.2% |
06
Mark scheme intelligence
2017–2024 mark scheme corpus
21TERMS
Tier 1 — frequently credited
| Term | Times credited | Years | Notes |
|---|---|---|---|
| index of diversity | 5 | 2017, 2018, 2022, 2023 | |
| species richness | 4 | 2017, 2023, 2024 | |
| representative | 3 | 2017, 2018, 2019 | |
| number of species | 3 | 2017, 2018, 2019 |
Tier 2 — sometimes credited
| Term | Times credited | Years | Notes |
|---|---|---|---|
| random sampling | 2 | 2017 | |
| no correlation | 2 | 2020, 2024 |
Commonly rejected language
| Term | Times rejected | Years | Why rejected |
|---|---|---|---|
| inappropriate sampling (quadrats/random coordinates in field) | 1 | 2017 | |
| unqualified results being significant | 1 | 2017 | |
| N = number of species | 1 | 2017 | |
| percentage cover | 1 | 2017 | |
| counting individuals | 1 | 2017 | |
| number of each species | 1 | 2017 | |
| results are due to chance | 1 | 2017 | |
| results are not due to chance | 1 | 2017 | |
| P (unqualified) | 1 | 2017 | |
| in a population | 1 | 2018 | |
| abundance | 1 | 2018 | |
| number of individuals | 1 | 2018 | |
| single habitat described alone | 1 | 2018 | |
| qualitative description without data values | 1 | 2018 | |
| mark-release-recapture | 1 | 2018 |
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
- N in Simpson's index defined as the number of species rather than total number of individuals — in 2017, a concentrated error in the calculation mark was treating N as the species count; N is the total number of all individual organisms sampled, and n is the number of individuals of each species; inverting these values produces a wrong formula application (2017 P3 Q04.1)
- Statistical tests described as proving or demonstrating accuracy — in 2017, students stated that a statistical test "proves the results are accurate" or "shows the data is correct"; statistical tests assess whether an observed difference is likely due to chance given the null hypothesis; they do not verify accuracy of measurement or prove that a hypothesis is true (2017 P3 Q04.3)
- Low index of diversity interpreted as all species having similar low abundances — in 2023, when asked what a low diversity index indicated about the community, only 7% scored both marks; the correct interpretation is that one or a few species dominate the community numerically; many students wrote that all species had low numbers, which would actually produce a diversity index close to 1 (high diversity); a low index requires one species to be disproportionately abundant (2023 P3 Q05.2)
Vocabulary errors
- "Population" used instead of "community" when describing species richness — species richness refers to the number of different species in a community; a population is all individuals of one species in one area; answering that species richness measures diversity "in a population" fundamentally conflates the ecological levels and was rejected in 2018 (2018 P1 Q03.1)
- "Abundance" and "number of individuals" rejected in species richness definitions — species richness is the number of different species present; it is not a measure of how many individuals there are; some students incorporated abundance information into their definition, which was explicitly not credited (2018 P1 Q03.1)
- Unqualified probability statements rejected — "results are significant" and "results are due to chance" were both rejected in 2017; the mark requires referencing the significance level (p < 0.05) and comparing the calculated statistic to the critical value; unqualified probability language does not demonstrate understanding of the decision rule (2017 P3 Q04.3)
Application errors
- Quadrats and random coordinates suggested as sampling improvements in woodland — in 2017, students who proposed quadrats or random coordinate sampling in a question about woodland biodiversity earned no mark; in some woodland contexts the question required transects or other directional methods reflecting environmental gradients; suggesting the wrong method type demonstrated failure to read the ecological context of the question (2017 P3 Q04.3)
- Qualitative descriptions given instead of data-referenced conclusions — in 2018, a question requiring description of a trend in species diversity data was answered with statements like "species richness is high in habitat A" without referencing the numerical values; qualitative description without data values was rejected; mark schemes required students to cite specific figures or percentage differences (2018 P1 Q03.4)
- Methodology improvement answers missing sufficient specificity — in 2018, fewer than 2% scored both marks on a question asking how to improve the reliability of a biodiversity survey; students who wrote "increase the sample size" without specifying what aspect of the methodology to change, or who described a single habitat alone rather than identifying the multi-habitat comparison as the issue, lost both marks (2018 P1 Q03.4)
High-impact failures · examiner narrative
2017 P3 Q04.12 marks
Simpson's diversity index calculation. The calculation mark required correct N (total individuals) and n (individuals per species) values before substituting into the formula. Students who set N equal to the number of species produced a structurally wrong calculation. Others who correctly identified N and n still made arithmetic errors by copying observed values incorrectly or performing the division in the wrong order. The examiner noted that formula recall was not the issue — most students could write the formula — but variable identification and careful substitution determined whether the calculation succeeded.
2018 P1 Q03.42 marks
Methodology improvement for biodiversity survey. Fewer than 2% scored both marks. The question required identifying a specific flaw in the methodology and proposing a concrete improvement. Most students gave generic responses about increasing sample size or using more replicates without connecting these to the specific design described. The examiner flagged that students needed to identify that the single-habitat sampling approach was the problem, and that comparing multiple distinct habitats using the same method would be the improvement. Vague responses about "doing it more times" or "using a bigger area" did not engage with the methodological logic.
2023 P3 Q05.22 marks7%full marks
Interpretation of a low Simpson's diversity index. Only 7% scored both marks. The question asked what a low index value indicated about the species composition of the community. The dominant error was stating that all species present had low numbers — a misreading of what the index formula produces. A low index value is produced when one species accounts for a large proportion of all individuals; many different species each with low numbers actually produces a higher index. The examiner noted that students who had calculated the index correctly in other questions still interpreted the output incorrectly when asked to reason from the value rather than compute it.
08
Difficulty signals
Performance metric synthesis
32PP GAP
Mean accessibility
63.5%
Mean mastery
31.6%
Mean student strength
49.0%
The accessibility–mastery gap of 31.8 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), 3.4.6 ranks 2 of 6 sub-sections by mean mastery (1 = hardest). Mastery trajectory is broadly flat across the cohort window: 29.5% in 2017 → 33.2% in 2024 (+3.8 percentage points). Mean mastery was lowest in 2023 (16.0%) and highest in 2019 (41.2%).