Point-based marking
Discrete, creditable ideas
PAPER 1 · STRUCTURED QUESTION 4(a)
State one factor that could explain the lower surface salinity compared to 1000 m depth. [1]
Student answer
more rain and rivers dilute the top layer of water✓
Mark scheme check
✓
Matches accepted mark point: freshwater input (rainfall / river runoff) dilutes surface salinity. Wording differs from the mark scheme but the underlying idea is correct — full credit.
Score: 1 / 1
A near-miss, for comparison
the water is warmer at the top✗
–
Temperature affects density, not salinity directly — this answers a different (also valid) property than the one asked about.
Coaching note
This is a common mix-up at this stage: temperature and salinity are separate variables that both affect density. Worth reviewing which property each factor changes before the next practice set.
Score: 0 / 1
Reasoning-chain marking
Are the right ideas actually connected?
PAPER 1 · STRUCTURED QUESTION 4(b)
Explain how the halocline affects the density of seawater at this location. [3]
Weaker answer
salinity increases with depth so density increases too✗
✓Correctly states salinity increases with depth.
–Jumps straight to the conclusion (density increases) without naming the halocline or the salinity→density mechanism — reads as a memorized fact, not an explanation of why.
–No mention of stratification or resistance to mixing.
Score: 1 / 3
Stronger answer
as you go deeper past the halocline, salinity rises quickly, and because salinity increases density, the water below becomes denser and resists mixing with the layer above✓
✓Links halocline to a zone of rapid salinity change with depth.
✓States that increasing salinity increases density.
✓Connects the density change to stratification / resistance to mixing.
Score: 3 / 3 — all three ideas present and causally linked, which is what "explain" requires over "describe."
Levels-of-response marking
Graded against a band, not a checklist
PAPER 3 · ESSAY QUESTION 7
Evaluate the effectiveness of marine protected areas (MPAs) in preserving reef biodiversity. [8]
Student answer (condensed)
MPAs restrict fishing and boat traffic, which allows coral and fish populations to recover. Many MPAs have shown increased fish biomass within their boundaries. MPAs also protect breeding grounds for reef species. Enforcement is often carried out by local rangers or satellite monitoring.
Band placement
Level 2 of 4 — "relevant points made, limited development or linkage between them"
Coaching note
Every fact here is accurate, and that's not the issue. "Evaluate" specifically asks for a judgement — you list four true points about MPAs but never weigh a strength against a limitation (e.g., enforcement cost, or fish migrating outside boundaries where protection doesn't apply) to reach a conclusion. Add one paragraph that directly compares a strength to a limitation, then state a supported overall judgement, before this can move into Level 3–4.
Score: 4 / 8 — content is solid; structure is capped at description, not evaluation.
Calculation marking · error carried forward
Method is checked separately from the final number
PAPER 2 · DATA-HANDLING QUESTION 3
Calculate the Simpson's Diversity Index using the species count data in Table 1. [3]
Student working
Formula: D = 1 − Σ(n/N)²
Species counts used: 12, 9, 7 (Table 1 shows 8)
N = 28 (using student's own figures) → D = 0.64
Working check
✓Correct formula selected and correctly structured.
Species count transcribed:
7
→ should be 8, one-off transcription slip
✓Final value correctly calculated from the student's own (incorrect) figures — error carried forward applies, so the method mark is still awarded.
Coaching note
The arithmetic slip didn't cost you a mark this time because of error carried forward, but it's worth double-checking table transcriptions before calculating — this is an easy place to lose marks on a question where you otherwise know the method cold.
Score: 2 / 3 — full method credit (ECF applied); one mark held for the transcription error itself.