NCEA 91159: gene expression (Level 2 Biology)

What NCEA 91159 assesses

NZQA says gene expression in the standard (version 2) involves a selection from these ideas and processes:

• nucleic acid structure and the nature of the genetic code: nucleotides, complementary base pairing, triplets, codons, anticodons and redundancy
• the significance of proteins, as products of gene expression, with a gene coding for one polypeptide
• protein synthesis: transcription and translation, and the role of enzymes in controlling them
• the determination of phenotype via metabolic pathways
• the effect of the environment on the genotype through mutations
• the effect of the environment on the expression of the phenotype

The three grades go up in steps. Achieved defines, uses annotated diagrams or models to explain, and gives characteristics of or an account of gene expression. Merit gives a reason as to how or why biological ideas and processes affect gene expression. Excellence links biological ideas and processes about gene expression, and the explanation may involve justifying, relating, evaluating, comparing and contrasting, or analysing.

The NCEA 91159 exam in 2026 and 2027

NCEA 91159 is one of three Level 2 Biology externals, with 91156 (life processes at the cellular level) and 91157 (genetic variation). The 2026 exam is on Friday 20 November, in the morning session. NZQA's specifications for both years say the exam is on printed paper and 91159 is a 4-credit external.

• Three questions: you answer all three. NZQA's 2025 report says each question had bullet points to guide the structure of your answer, and the strongest candidates answered every bullet.
• Question style: you may need to interpret diagrams and new information, draw diagrams, and write responses of one or more paragraphs. Some questions are resource-based, and you may use annotated diagrams as evidence.
• Use the resource and go beyond it: the report says candidates who linked the resource material to their answers did better, and the highest grades added relevant detail that the resource did not give.
• Stay on the question: the report says material that is related to biology but outside what the question asks cannot be credited.
• Bases: NZQA says the bases are adenine, thymine, guanine, cytosine and uracil, and you should understand the relationship between them. Gene mutations may use examples from plants or animals, including humans.

How NCEA 91159 is marked

Each of the three questions is scored N0 to E8 and the scores add to a total out of 24. The 2025 report describes questions on substitution mutations, transcription and translation, and a chlorophyll pathway, so credit came from following a chain from DNA to enzyme to phenotype.

NCEA 91159 cut scores

There was no movement at all in this standard. Achieved began at 8, Merit at 14 and Excellence at 19 in every year. The scores are where each grade begins, out of 24.

Cut scores 2025

2025 schedule: Achieved from 8, Merit from 14, Excellence from 19. The same as 2024.

Cut scores 2024

2024 schedule: Achieved from 8, Merit from 14, Excellence from 19. The same as 2023.

Cut scores 2023

2023 schedule: Achieved from 8, Merit from 14, Excellence from 19. The same as 2022.

Cut scores 2022

2022 schedule: Achieved from 8, Merit from 14, Excellence from 19. The same as 2021.

Cut scores 2021

2021 schedule: Achieved from 8, Merit from 14, Excellence from 19.

Worked examples at each grade

Achieved: transcription and translation

Take a DNA template strand 3′ TAC TTT GGG 5′. RNA polymerase copies it into mRNA using complementary pairs: A pairs with U, T with A, and C with G. Ribosomes read the mRNA in codons, and each codon is matched by a tRNA anticodon:

• mRNA: 5′ AUG AAA CCC 3′
• tRNA anticodons: UAC, UUU, GGG
• amino acids: methionine, lysine, proline

Check the sequence in the DNA Translator, which reads the coding strand ATGAAACCC.

Merit: the effect of substitution mutations

Change one base in the lysine codon AAA. Because there are 64 codons but only 20 amino acids, the code is redundant, and different codons can code for the same amino acid:

• AAA to AAG still codes for lysine. This is a silent mutation, and the protein is unchanged.
• AAA to AAU codes for asparagine instead. This is a missense mutation, and the protein has a different amino acid, which may or may not change how it folds.
• AAA to UAA is a stop codon. This is a nonsense mutation, and the polypeptide stops early.

A substitution changes one codon only, so the other amino acids are the same and the length does not change, except when a stop codon appears. That is different from an insertion or deletion, which shifts the reading frame. The DNA Translator shows the silent change at base 6. NZQA's 2025 report says Merit candidates explained redundancy and linked it to silent mutations.

Excellence: metabolic pathways and the environment

A pigment is made in two steps. Gene 1 codes for enzyme 1, which turns substance P into substance Q, and gene 2 codes for enzyme 2, which turns Q into the pigment. A mutation in gene 1 changes the amino acid sequence, so enzyme 1 folds differently and its active site no longer fits P. Q is never made, enzyme 2 has no substrate, and the pigment is missing. A mutation in gene 2 has the same final effect for a different reason. In 2025, NZQA's questions used this pattern with chlorophyll, where the leaves turn yellow when either enzyme is not working, and where magnesium, an environmental factor, was needed for enzyme 2 to work.

The environment also acts on a normal genotype. In a Himalayan rabbit the enzyme that makes dark pigment only works at low temperatures, so the rabbit has dark fur on its cooler ears, nose and feet and white fur elsewhere. Every cell has the same genes, but their expression differs. Excellence links the mutation, the protein, the pathway and the phenotype in one chain.

Now name some mutations in our Genetics and DNA course, then press Mark to check your answer in the course:

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

The Level 2 Biology track above is a short timed mock of 8 questions, not a full exam and not written by NZQA (NCEA Level 2 Biology). It covers nucleic acids and DNA replication and protein synthesis, which support 91159, but mutations and metabolic pathways get little coverage, and the effect of the environment on the phenotype none. For those use our Genetics and DNA course.

Is NCEA 91159 changing?

NZQA's 2027 specification keeps the five bases (including uracil) and mutation examples from plants and animals. Year 12 changes to the NZ Certificate of Education in 2029.

Common mistakes in NCEA 91159

• Describing a mutation without its effect. NZQA's 2025 report says higher grades linked the mutation to the amino acid sequence, the protein's shape and function, and the symptoms.
• Forgetting the length stays the same. Most candidates did not mention the other amino acids or the unchanged length of the polypeptide for a substitution.
• Skipping why DNA cannot be translated directly. Connect transcription and translation to the reason.
• Restating the question. The report says many candidates only restated the information given and did not explain the metabolic pathway.
• Missing the environmental factor. A factor such as magnesium can stop an enzyme working even when the gene is normal.

Read next

New Zealand · NCEA Level 2NCEA Level 2 Biology: standards, exam date and practiceNCEA Level 2 Biology explained: cell processes, genetic variation and gene expression externals, the internals, the 2026 exam date and worked examples.