NCEA 91605: evolutionary processes and speciation (Level 3 Biology)

What NCEA 91605 assesses

NZQA's standard says the evolutionary processes involve these biological ideas:

• the role of mutation and of gene flow
• the roles of natural selection and genetic drift
• modes of speciation: sympatric and allopatric
• reproductive isolating mechanisms: geographical, temporal, ecological, behavioural and structural barriers, and polyploidy
• patterns such as divergence, convergence, adaptive radiation, co-evolution, punctuated equilibrium and gradualism

Scientific evidence may include examples from New Zealand's flora and fauna, chosen from fossils, comparative anatomy (homologous and analogous structures), molecular biology (proteins and DNA analysis) and biogeography. Achieved uses biological ideas or evidence to describe the processes. Merit explains how or why they lead to speciation. Excellence links ideas and evidence, which may involve justifying, relating, evaluating, comparing and contrasting, or analysing.

The NCEA 91605 exam in 2026 and 2027

NCEA 91605 is one of three Level 3 Biology externals, with 91603 and 91606. The 2026 exam is on Tuesday 17 November, in the afternoon session. NZQA's 2027 timetable is not out yet: it says exams run from 9 November to 3 December 2027. The 2026 and 2027 specifications match: resource-based questions, graphical and tabulated data, and annotated diagrams allowed. They name terms to know: directional, stabilising and disruptive selection, genetic diversity, allele frequency change, mitochondrial and nuclear DNA evidence, phylogeny, clades and ring species. Geological events that drive speciation include tectonic movement, glaciation, orogeny and sea level change.

How NCEA 91605 is marked: grade score marking

Each question scores N0 to E8 and the three add to 24. Because the standard is 4 credits and evidence points are counted, a single answer that names the isolating mechanism and links it to the resource can bank two or three points at once.

NCEA 91605 cut scores

These are NZQA's cut scores for the total out of 24, taken from each year's assessment schedule. Over these five years Achieved needed 8 in every year but one (7 in 2023), Merit 14 (13 in 2023) and Excellence 19. The 2026 cut scores will appear in NZQA's 2026 schedule once the exam has been marked.

Worked examples at each grade

Achieved: describe a mode of speciation

Describe allopatric speciation. A population is split by a geographical barrier, such as a glacier or rising sea. The two groups can no longer interbreed, so gene flow between them stops. Over time they accumulate different mutations and may become separate species.

Merit: explain how and why

Two populations of an alpine insect have been separated by glaciation for many generations. Explain why they may now be different species. Each population has different mutations, and natural selection favours different alleles in its different habitat. Genetic drift also changes allele frequencies by chance, more strongly in a small population. With no gene flow, the gene pools diverge. Reproductive isolating mechanisms can then arise, such as breeding at different times of year (temporal isolation) or different courtship behaviour (behavioural isolation), so if the barrier disappeared the groups would not interbreed. Individuals that cannot produce fertile offspring together are, by definition, different species.

Excellence: justify a mode with evidence

A new plant species arose from a hybrid of two species growing together, with no geographical barrier. Justify which mode of speciation it shows. This is sympatric speciation. The hybrid had a doubled chromosome number (polyploidy), so it could not form fertile offspring with either parent: a triploid backcross is sterile. It was reproductively isolated in a single generation, which is a reproductive barrier, not a geographical one. Because the parent species occupied the same area throughout, allopatric speciation is ruled out. Molecular evidence supports the claim: DNA analysis showing that the hybrid carries genes from both parents, and a phylogeny placing it as a sister lineage to them.

Check one idea with a question on the page:

Exam answers

The answers and a worked mark scheme come with today's paper once it is marked. We do not publish official or past paper answers. Every question on the daily paper is our own.

Use the daily paper as a practice exam

Uni-Sine publishes a free daily paper on the NCEA Level 3 Biology track. It is a short timed paper of 8 questions worth 25 to 35 marks, not a full NCEA exam, and it is not written by NZQA. Its topics include evolution and speciation, along with inheritance and Hardy Weinberg, which supports the allele frequency ideas in 91605. See the NCEA Level 3 Biology guide for the whole subject.

Common mistakes in NCEA 91605

NZQA's 2025 report on Level 3 Biology says candidates who were Not Achieved commonly:

• Defined terms inaccurately or too loosely for Level 8 of the curriculum, sometimes without relating them to the question.
• Repeated the context from the resource without adding information or explanation.
• Gave examples unrelated to the question. Use the resource material, and link to it.
• Skipped questions. The report says some candidates did not attempt all three, and that poor handwriting made some answers hard to read.

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New Zealand · NCEA Level 3NCEA Level 3 Biology: standards, exam date and practiceNCEA Level 3 Biology explained: externals on responses to the environment, speciation and human evolution, the internals, the 2026 exam date and examples.