Mark it yourself: QCE Biology short responses

How to use this pack

The QCAA marking guide for Biology is unusually transparent: every short-response mark is listed as a separate element. This pack uses the 2024 Biology external assessment marking guide and the 2024 Biology subject report to show how four common question types are marked. Each type has an original practice question with our own full-mark sample answer (written by ExamExplained, not an official QCAA response), the errors that cost marks, and a self-marking prompt.

These examples come from the 2024 external assessment. QCAA has introduced new senior syllabuses, so check QCAA's current syllabus and assessment information for your cohort; the way individual marks are matched to elements of a response is the part to learn from here.

How the QCAA Biology marking guide works

• Each mark is a separate element. For example, for a 2024 SDI question: "determines SDI as 0.61 [1 mark]" and "provides appropriate working [1 mark]".
• Follow-through is allowed. The guide states that where "an error in the prior section of working is used later in the response, a mark (or marks) for the rest of the response can still be awarded" if it still demonstrates the correct understanding or skill.
• Data must be used. Inference questions pair "infers..." with "justifies inference using SDI data" or "justifies response using data".
• Read the cues. The 2024 subject report recommended "emphasising the importance of cueing factors such as the cognitive verb, the number of marks, key terms in the question and relevant stimulus when planning responses", and correct terminology, "particularly when describing genetics concepts, e.g. 'allele' vs. 'gene'".

Type 1: calculations with working (2 marks)

Official pattern (2024, Paper 1, Question 21a): "determines SDI as 0.61 [1 mark]"; "provides appropriate working [1 mark]". Energy transfer efficiency (Question 26a) and population growth rate (Paper 2, Question 3) were marked the same way.

Practice question (ours). A rocky-shore survey recorded four species: X, 12 individuals; Y, 8; Z, 5; W, 5. Calculate Simpson's diversity index using $SDI = 1 - \frac{\sum n(n - 1)}{N(N - 1)}$. (2 marks)

Our sample answer (2 marks).

N = 12 + 8 + 5 + 5 = 30

$\sum n(n - 1) = 12(11) + 8(7) + 5(4) + 5(4) = 132 + 56 + 20 + 20 = 228$

$SDI = 1 - \frac{228}{30 \times 29} = 1 - \frac{228}{870} = 1 - 0.26 = 0.74$

Type 2: infer and justify with data (2 marks)

Official pattern (2024, Paper 1, Question 21b): "infers that species evenness decreased over the 10-year period [1 mark]"; "justifies inference using SDI data [1 mark]". Paper 2, Question 8b followed the same pattern: "infers that organic matter lowers soil pH [1 mark]"; "justifies response using data [1 mark]".

Practice question (ours). After a severe storm, the same rocky shore was surveyed again: X, 25 individuals; Y, 3; Z, 1; W, 1. The SDI was 0.30, compared with 0.74 before the storm. Infer how the storm affected the community, and justify your inference using the data. (2 marks)

Our sample answer (2 marks).

The storm reduced species evenness, while species richness was unchanged. All four species were still present (richness = 4 before and after), but the community became dominated by species X (25 of 30 individuals, compared with 12 of 30 before), and the SDI fell from 0.74 to 0.30. Because SDI reflects both richness and evenness, and richness stayed the same, the fall in SDI shows that evenness decreased.

Type 3: explaining a process step by step (3 marks)

Official pattern (2024, Paper 1, Question 22b): "explains the observed trends, referring to phenotypic variation [1 mark], differential survival and reproduction [1 mark], change over time [1 mark]". Paper 2, Question 7a (habitat fragmentation and speciation) similarly gave one mark each for isolation, disrupted gene flow and how this leads to speciation.

Practice question (ours). When the myxoma virus was released in Australia in 1950 to control rabbits, it killed most infected rabbits. Over the following decades, a growing proportion of wild rabbits survived infection. Explain this change. (3 marks)

Our sample answer (3 marks).

• Variation: the rabbit population contained genetic variation, and a small number of rabbits carried alleles that made them more resistant to the myxoma virus.
• Differential survival and reproduction: the virus acted as a selection pressure. Resistant rabbits were more likely to survive infection and reproduce, while susceptible rabbits died before reproducing.
• Change over time: resistant rabbits passed the resistance alleles to their offspring, so over many generations the frequency of these alleles in the gene pool increased, and a greater proportion of the population survived infection.

Type 4: describing a method and minimising bias (3 marks)

Official pattern (2024, Paper 1, Question 21c)

"describes an appropriate surveying technique [1 mark]"; "identifies one strategy to minimise bias [1 mark]"; "identifies a second strategy to minimise bias [1 mark]". The sample response used randomly placed quadrats, sampling at least 10% of the site, and a random-number generator to position quadrats.

Practice question (ours)

Describe how the capture-recapture method could be used to estimate the size of a skink population in a nature reserve, and identify two ways to make the estimate more reliable. (3 marks)

Our sample answer (3 marks)

• Method: capture a sample of skinks, mark each one harmlessly (for example, a small dot of non-toxic paint), record the number marked (M) and release them where they were caught. After enough time for them to mix back into the population, capture a second sample, count the total caught (n) and the number already marked (m), and estimate the population using $N = \frac{Mn}{m}$.
• Reliability 1: use marks that do not rub off and do not make skinks more visible to predators, so marked and unmarked skinks are equally likely to be recaptured.
• Reliability 2: keep the interval between captures short enough that births, deaths and migration are unlikely to change the population, and repeat the recapture several times and average the estimates.

Your self-marking prompt

Paste this into ChatGPT or another AI tool, with the question and your answer. Add the elements from the matching table above, or, for a past paper, the itemised marks from the QCAA marking guide.

You are an experienced QCAA Biology external assessment marker. Mark my
answer using the itemised marking elements below. Award each mark only if
that element is clearly present and correct. Apply follow-through only
where an earlier error is carried forward correctly.

Question ([number] marks): [paste the question and any data]

Marking elements:
[paste one line per mark, e.g. "determines SDI [1 mark]",
"provides appropriate working [1 mark]"]

My answer:
[paste your answer]

1. Go through each element and quote the part of my answer that earns
   it, or say that it is missing.
2. Check every calculation and every biological term (for example,
   allele versus gene).
3. Give my total mark.
4. Tell me exactly what to add to earn any missing mark. Do not rewrite
   my answer.

Next steps

• Practise the multiple-choice section with the harder exam-style QCE Biology quiz.
• Revise the content in the Unit 3 deep dive and the Unit 4 deep dive.
• Then complete a QCAA past paper and mark it with its published marking guide.