Mark it yourself: HSC Biology short and extended responses

How to use this pack

You improve fastest when you can mark your own answers the way a NESA marker would. This pack takes four question types that come up in almost every HSC Biology Section II and shows, for each one:

1. what the official NESA marking criteria look like (quoted from real marking guidelines, with links)
2. what earns each mark
3. an original practice question with our sample answer at the top mark (written by ExamExplained, not an official NESA exemplar)
4. the errors that most often cost marks
5. a self-marking prompt you can paste into NSWEduChat (if your school gives you access), ChatGPT or another AI tool.

How NESA marking guidelines work

Every Section II question in the published marking guidelines has a criteria table. A few features are consistent from year to year:

• The verb sets the ceiling. The top criterion repeats the verb from the question. In the 2025 guidelines a 2-mark question tops out at "Outlines how mechanism B maintains homeostasis", and a 3-mark mutation question tops out at "Explains the type of mutation" with "Makes reference to the data provided". An outline cannot earn an explain mark.
• Levels are holistic. For bigger questions a level lists several bullets ("Demonstrates an extensive understanding ... Provides a relevant judgement"). Markers place your answer at the level it best fits, so one missing element (usually the judgement) drops a whole level.
• The floor is "Provides some relevant information". One correct, relevant idea almost always earns 1 mark. Never leave a Biology question blank.
• The sample answer is not the only answer. Guidelines often add "Answers could include", listing other acceptable examples. Any accurate, relevant response that meets the criteria earns the marks.

The verbs matter because the criteria are written in them. NESA's glossary defines them:

Type 1: the 2 to 3 mark "explain" question

What the official criteria look like. In the 2025 HSC Biology guidelines, Question 31(b) was marked: "Explains the type of mutation" and "Makes reference to the data provided" (3 marks); "Outlines the mutation with reference to the data provided" (2 marks); "Provides some relevant information" (1 mark). Short questions follow this ladder: full verb for top marks, a lesser verb for the middle, relevant information for 1.

Mark by mark (3-mark explain):

Practice question (ours). Explain how a single base substitution in a gene can change the function of the protein it codes for. (3 marks)

Our sample answer (top mark).

A substitution replaces one base in a DNA triplet, so after transcription one mRNA codon is different. If the new codon codes for a different amino acid (a missense mutation), a different amino acid is added during translation. Because a protein's three-dimensional shape depends on its amino acid sequence and the interactions between R groups, this can change how the polypeptide folds, altering an active site or binding site so the protein works less well or not at all. For example, in sickle cell anaemia one substitution replaces glutamic acid with valine in the beta chain of haemoglobin, changing the shape of red blood cells. If the new codon is a stop codon (a nonsense mutation), the polypeptide is shortened and usually non-functional.

Why it earns 3: every step is linked (DNA to mRNA to amino acid to shape to function), and the example shows the chain working in a real case.

Other common mark-losing errors: calling a substitution a frameshift; writing "the gene changes the protein" without mentioning transcription or translation; saying every substitution changes the protein (silent mutations exist because the code is redundant).

Type 2: evaluating a claim using data (3 to 4 marks)

What the official criteria look like. In the 2025 guidelines, Question 25 asked students to evaluate a product statement using data. The top level (3 marks) was "Provides an accurate evaluation of the product statement" and "Demonstrates a sound understanding of the data provided"; 2 marks for "some understanding of the product statement and the data provided"; 1 mark for "some relevant information". The top mark needs both a judgement on the claim and correct use of the numbers.

Mark by mark (4-mark version):

Practice question (ours). A hand sanitiser is labelled "kills 99.9% of germs". A student pressed one hand onto an agar plate after each treatment and counted bacterial colonies after 48 hours at 25 °C: no treatment, 240 colonies; washing with soap and water for 20 seconds, 18 colonies; sanitiser, 31 colonies. Each treatment was done once. Evaluate the label's claim using the data. (4 marks)

Our sample answer (top mark).

The data do not support the claim. Colonies fell from 240 to 31 after using the sanitiser, a reduction of (240 minus 31) / 240 = about 87%, well short of 99.9%, which would leave fewer than one colony. The sanitiser was also less effective than soap and water (18 colonies, about a 92% reduction). However, the evidence is limited: each treatment was done only once, on one hand, so the results may not be reliable, and agar at 25 °C only shows bacteria that grow in those conditions, not viruses or other "germs" the label refers to. Repeated trials with several people would be needed to evaluate the claim confidently, but on this evidence the claim is not supported.

Other common mark-losing errors: judging the claim true because the sanitiser "reduced bacteria"; ignoring the control (no treatment); forgetting that one trial limits reliability; treating colony counts as a measure of viruses.

Type 3: genetics calculations with working (3 marks)

What the official criteria look like. In the 2024 guidelines, Question 28(a) (a cystic fibrosis probability question) was marked: 3 marks for "the correct parental genotypes and suitable working with a Punnett square" and "the correct probability"; 2 marks for "the correct probability with some correct working" or "the correct parental genotypes with suitable working"; 1 mark for relevant information. A bare answer with no working cannot reach full marks.

Mark by mark:

Practice question (ours). Cystic fibrosis is an autosomal recessive condition. Two parents who do not have cystic fibrosis have a first child who does. Their second child does not have cystic fibrosis. Calculate the probability that the second child is a carrier. Show your working. (3 marks)

Our sample answer (top mark).

Key: F = normal allele, f = cystic fibrosis allele. The first child is ff, so each parent passed on an f allele. Both parents are unaffected, so both are Ff.

	F	f
F	FF	Ff
f	Ff	ff

The second child does not have cystic fibrosis, so they are FF, Ff or fF (three equally likely outcomes; ff is ruled out). Two of these three are carriers. Probability the second child is a carrier = 2/3.

Other common mark-losing errors: no key for the alleles; parental genotypes not justified from the affected child; using X-linked notation for an autosomal condition.

Type 4: the 7-mark extended response with a judgement

What the official criteria look like. In the 2025 guidelines, Question 30(b), a 7-mark question on the impacts of genetic technologies for society, was marked:

The 2024 guidelines used the same ladder (extensive, thorough, sound, some) for a 7-mark discussion of two biotechnologies. Two things decide your band: depth (extensive means specific mechanisms, named examples and consequences) and whether there is a judgement. With no judgement, the best possible result is 3 to 4 marks.

Practice question (ours). Assess the effectiveness of TWO strategies used to control the spread of a named infectious disease. (7 marks)

Our sample answer (top band).

Malaria is caused by the protist Plasmodium (most deadly species P. falciparum) and is transmitted when an infected female Anopheles mosquito bites a person. Control strategies are effective if they break this transmission cycle, can be sustained, and reach the people most at risk. Judged this way, insecticide-treated bed nets are highly effective, while antimalarial drugs are effective for individuals but increasingly limited as a control strategy.

Insecticide-treated nets break transmission at the vector stage. Anopheles mosquitoes mostly bite at night, so a net over a sleeping person blocks bites, and the insecticide kills mosquitoes that land on it, reducing the vector population for the whole community. Large randomised trials, summarised in Cochrane reviews, found that treated nets reduced child deaths from all causes by roughly a sixth compared with no nets. Nets are cheap and simple to distribute. Their effectiveness is limited because they must be replaced as the insecticide wears off, not everyone uses them every night, and mosquitoes resistant to pyrethroid insecticides are now widespread, which is why newer nets combine two active ingredients.

Antimalarial drugs, especially artemisinin-based combination therapies, act on the pathogen inside the host. Prompt diagnosis and treatment cure most patients and, by clearing parasites from the blood, reduce the number of people who can pass the parasite to mosquitoes. However, treatment works only after infection, depends on access to diagnosis and health care, and is threatened by drug resistance: partial resistance to artemisinin appeared in South-East Asia and has since been reported in parts of Africa. Using combinations of drugs slows resistance but does not stop it.

Overall, bed nets are the more effective strategy for controlling spread because they prevent transmission before infection and protect whole communities cheaply, while drugs mainly protect the individual and are losing effectiveness as resistance spreads. The most effective control combines both, alongside newer measures such as the malaria vaccines now recommended by the World Health Organization.

Why it earns 7: it names the disease, pathogen and vector; explains HOW each strategy breaks transmission; gives evidence and limitations for each; sets criteria for "effective" in the first paragraph; and makes a clear, supported judgement at the start and the end.

The errors that cost the most marks in 7-mark questions:

• No judgement. Two good descriptions with no "therefore X is more effective" sit at 3 to 4 marks.
• A judgement with no reasons. "Vaccination is very effective" is not supported until you say why (for example, herd immunity reduces transmission).
• No named example. "A disease" or "a pathogen" reads as general knowledge, not extensive understanding.
• Only one strategy when the question asks for two.
• Writing everything you know. Markers reward relevance to the question, not length.

Your self-marking prompt

Copy this into NSWEduChat, ChatGPT or another AI tool. Replace the parts in square brackets. Paste the criteria from the matching question type above (or from a real NESA marking guideline if you are doing a past paper).

You are an experienced HSC Biology marker. Mark my answer strictly against
the marking criteria below. Do not award a mark the criteria do not allow,
and do not reward length.

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

Marking criteria:
[paste the criteria table, one line per mark level]

My answer:
[paste your answer]

1. For each criterion, quote the words in my answer that meet it, or say
   clearly that it is not met.
2. Check the biology for errors and list any incorrect statements.
3. Give my mark and name the criteria level it matches.
4. Tell me the single most important change that would lift my mark by one
   level. Do not rewrite the whole answer for me.

Next steps

• Practise the multiple-choice half with the harder exam-style HSC Biology quiz.
• Take one real past paper, write the Section II answers under time, then mark them with the official guideline for that year from the NESA exam papers page.
• Revise the content behind these question types in the Modules 5 and 6 guide and the disease guide.