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QLDBiology2024

QCE Biology 2024

Walkthrough of the 2024 QCE biology exam: what it assessed, strategy tips, and the common errors flagged in the official marker report.

Marks
97
Time
180 min
Authority
QCAA
Updated
Open the official PDF Official marking notes
Key fact

This paper was set on the 2019 QCAA syllabus. From the 2026 external assessments the 2025 syllabus applies, so some content and the exam format have changed. It is still useful practice, but check the current QCAA Biology syllabus and QCAA's 2026 key changes before relying on it. The mark and timing figures at the top of this page are a guide based on the 2024 papers (two papers, each with 90 minutes of working time), not QCAA's official structure for every year. Marks and question types vary, so use QCAA's own paper.

What this paper assessed

This QCAA Biology external assessment is sat as more than one paper. It assesses Unit 3 (Biodiversity and the interconnectedness of life) and Unit 4 (Heredity and continuity of life):

  • Unit 3: describing and classifying biodiversity, ecosystem dynamics (energy flow, nutrient cycling, population sampling and ecological niches), and the effects of human activity and environmental change.
  • Unit 4: DNA structure and replication, gene expression (transcription and translation), inheritance and variation, mutations, and the mechanisms and evidence of evolution (natural selection, speciation, biotechnology and population genetics).

The paper combines multiple choice with short-response and an extended-response item, with several questions presenting an unfamiliar diagram or dataset that requires applying core principles. The 2024 paper leaned harder on application items where the surface context was unfamiliar but the underlying skill was core.

Structure and timing

QCAA sets the external assessment as more than one paper, and the number of marks, the sections and the question types differ from year to year. Open the official paper for the exact structure of this year; the marks and time shown at the top of this page are a guide only.

  • Pace by marks. Share your working time in proportion to the marks on offer, so a 6-mark item gets about three times the time of a 2-mark item. Flag any multiple choice item that runs long and return to it.
  • Use perusal time. Scan for the data-heavy items and the longest calculations or extended responses so you can plan them early.
  • Subject habits. For a multi-mark explain or evaluate item, plan three or four linked points so each marking criterion is addressed, and keep a few minutes at the end to check that every explain or justify answer gives a reason, not just a description.

Worked practice questions (exam-style)

Worked example

Question 1 (4 marks): A length of DNA has the template (transcribed) strand 3'-TAC GGA TTC ACT-5'. Determine the mRNA sequence and explain how the cell ensures the correct amino acid is added during translation.

Transcription pairs RNA bases to the template (A-U, T-A, G-C, C-G), read 3'→5' on the template to give 5'→3' mRNA:

Template: 3'-TAC GGA TTC ACT-5'
mRNA: 5'-AUG CCU AAG UGA-3'

During translation, each mRNA codon is read in the ribosome. A tRNA carrying a specific amino acid has an anticodon that is complementary to the codon (e.g. codon AUG pairs with tRNA anticodon UAC, bringing methionine). Complementary base pairing between codon and anticodon ensures the correct amino acid is delivered in the correct order, so the polypeptide's sequence is determined by the mRNA. (Note UGA is a stop codon, ending translation.)

Worked example

Question 2 (5 marks): A population of beetles lives on bark that becomes darker after a wildfire. Over several generations the proportion of dark beetles increases. Explain this change using the theory of natural selection.

  1. Variation: the beetle population shows heritable variation in colour (light and dark), arising ultimately from mutation and recombination.
  2. Selection pressure: after the fire the darker bark means light beetles are more visible to predators, while dark beetles are better camouflaged.
  3. Differential survival and reproduction: dark beetles are more likely to survive predation and reproduce, passing the dark-colour alleles to offspring; light beetles leave fewer offspring.
  4. Change in allele frequency: over successive generations the frequency of dark-colour alleles increases in the population's gene pool.
  5. Outcome: the population becomes better adapted to the new environment - an example of directional selection. (No individual beetle "changes colour"; the population's composition shifts.)
Worked example

Question 3 (6 marks): An ecologist used the capture-mark-recapture method on a frog population. They captured and marked 60 frogs, then in a second capture of 80 frogs, 24 were marked. Estimate the population size and evaluate one assumption of the method.

Use the Lincoln index: N=M×CRN = \dfrac{M \times C}{R}, where MM = first marked (60), CC = total in second capture (80), RR = marked recaptured (24).

N=60×8024=480024=200 frogs.N = \frac{60 \times 80}{24} = \frac{4800}{24} = 200\ \text{frogs}.

Estimated population ≈200\approx \mathbf{200} frogs.

Evaluation of an assumption: the method assumes no births, deaths, immigration or emigration between captures, and that marked individuals mix randomly back into the population. If marking made frogs more visible to predators (reducing RR), the estimate would be too high; if there was insufficient time for marked frogs to redistribute, sampling bias would reduce validity. Improving reliability requires allowing mixing time and minimising the effect of the mark on behaviour.

Common errors students made

The 2024 QCAA marker report flagged that students frequently:

  • confused antigen and antibody, and B cells with T cells, in immunity items;
  • mixed up transcription and translation steps and locations;
  • gave conclusion statements that ignored the data shown;
  • forgot to identify the independent and dependent variables in experimental questions.

Further subject-specific traps:

  • Describing evolution as individual organisms "adapting" rather than allele frequencies changing in a population.
  • Misreading the direction of base pairing (template strand vs mRNA, and DNA's T vs RNA's U).
  • Stating a trend without quoting a specific value and unit from the graph or table.
  • Treating correlation as causation in ecological data and ignoring the command word (describe vs explain vs evaluate).

How to use this paper

  1. The 2024 sitting was two papers of 90 minutes working time each, with 10 minutes of perusal in the booklets. QCAA's 2026 timetable has two papers, each with 5 minutes of perusal and 90 minutes of working time (check the current QCAA syllabus for your sitting). Sit one paper at a time under timed conditions, pacing each by marks.
  2. Self-mark strictly against the official marking guide and the QCAA marker report using the links at the top of this page - award a mark only where the criterion is explicitly met.
  3. Rewrite one extended response per session so it names the principle, applies it to the scenario, and quotes data to support the conclusion.
  4. Keep a glossary of any term used loosely (e.g. "immunity", "expression", "selection") and define each precisely.

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