The AQA 25-Mark Biology Essay: An Examiner’s Guide to Full Marks

What the Essay Actually Is (and Is Not)

The 25-mark essay appears as the final question on AQA Biology Paper 3 (7402/3). You choose one title from two options and write a continuous essay in approximately 45 minutes.

It is worth 25 marks out of 78 on Paper 3 — that is 32% of the entire paper from a single question. Across your whole A-Level, it accounts for roughly 10% of your final grade. No other single question on any biology paper carries anywhere near this weight.

But here is what most students get wrong about the essay: it is not a test of how much biology you can write. It is a test of whether you can select relevant material from across the specification and link it coherently to a central theme.

AQA themselves describe it as “an exercise in synopsis, not an excuse for students to tell examiners everything they know about just one or two topics.” Students who treat it as a knowledge dump consistently score Level 2–3. Students who treat it as a focused, structured argument consistently score Level 4–5.

The 5-Level Mark Scheme Explained

Unlike 6-mark questions which use three levels, the essay uses five levels. Understanding what each level looks like is the first step to consistently hitting Level 5.

Notice the pattern. The difference between levels is primarily about three things:

1. Breadth — how many different specification topics you cover
2. Relevance — whether your content is linked to the essay title or just a knowledge dump
3. Level of detail — A-level precision versus GCSE generality

The jump from Level 4 to Level 5 adds one extra requirement: evidence of reading beyond the specification. I will cover exactly what this means and how to achieve it later in this article.

The AO1/AO2 Split That Most Students Miss

This is where the vast majority of students lose marks, and most teachers do not explain it clearly enough.

The essay is worth 13 marks for AO1 and 12 marks for AO2. Here is what that means in practice:

• AO1 (13 marks) = demonstrating knowledge and understanding of scientific ideas and processes. This is the biology itself — the facts, the mechanisms, the definitions.
• AO2 (12 marks) = applying knowledge and understanding to unfamiliar or familiar contexts. In the essay, this means explicitly explaining why your AO1 content is relevant to the essay title.

Consider an essay titled “The importance of shapes fitting together in cells and organisms.” Here is the difference between AO1 and AO2:

• AO1: “Enzymes have a tertiary structure with a specific active site shape. The substrate binds to the active site by forming an enzyme-substrate complex.”
• AO2: “This complementary shape is important because it gives enzymes their specificity — each enzyme catalyses only one reaction, allowing metabolic pathways to be precisely controlled.”

The AO1 states the biology. The AO2 explains why that biology matters in the context of the essay title. Students who only write AO1 content — just stating facts — can never score above about 13/25, no matter how accurate their biology is. The other 12 marks require you to link every piece of content back to the essay title.

The 5-Minute Planning Method

Spending 5 minutes planning the essay is not optional if you want Level 5. Here is the method I teach.

The Paragraph Structure That Gets Level 5

Here is the structure I recommend for each topic area in your essay. It ensures you hit both AO1 and AO2 for every point.

For an essay titled “The importance of shapes fitting together in cells and organisms”, your plan might look like this:

This gives you 5 topic areas (enzymes, immunity, hormones, DNA replication, translation), each with AO1 and AO2, plus a beyond-spec example (wobble base pairing). That is a Level 5 structure.

How to Include “Beyond the Specification”

The Level 5 descriptor requires “evidence of reading beyond specification requirements.” This phrase intimidates students, but it should not.

You do not need to reference cutting-edge research papers. You need one or two examples that demonstrate you have read or learned something not explicitly in the AQA textbook. Here are practical ways to achieve this:

Named examples not in the specification

The specification talks about enzymes, but it does not name every enzyme. Referencing a specific named enzyme in a relevant context — for example, “restriction endonucleases recognise specific palindromic DNA sequences” in an essay about shapes — counts as beyond-spec if the specification does not name that enzyme.

Real-world applications

Mentioning CRISPR-Cas9 in an essay about gene expression, or referencing mRNA vaccine technology in an essay about the immune response, shows you have read beyond the textbook. These do not need to be detailed — a sentence or two showing awareness is sufficient.

Named organisms

Using a specific organism to illustrate a point — for example, the Venus flytrap for rapid plant responses, or the axolotl for regeneration — adds beyond-spec value when those organisms are not in the specification.

Where to find these examples

• New Scientist and Biological Sciences Review — even reading headlines builds awareness
• BBC Bitesize “In the News” sections — short, accessible summaries of recent biology
• Your tutor or teacher — ask them to share one interesting fact per topic that goes beyond the textbook

The Mistakes That Cap Students at Level 3

Level 3 (11–15 marks) is where the majority of students end up. Here is why, and how to break through.

1. Only covering 2–3 topic areas

This is the most common reason for Level 3. AQA requires content from “several” areas, defined as a minimum of four. If you write brilliantly about enzymes, antibodies, and DNA — three topic areas — you are capped at Level 3 regardless of quality. You need at least four, ideally five or six.

2. Writing AO1 without AO2

Students write page after page of accurate biology without ever linking it to the essay title. Remember, 12 of the 25 marks are for application. If your essay reads as “here are some facts about biology” rather than “here is why these biological processes are important for [essay title],” you are leaving nearly half the marks on the table.

3. GCSE-level detail

“Enzymes speed up reactions” is GCSE. “Enzymes lower the activation energy by stabilising the transition state of the enzyme-substrate complex within the active site” is A-Level. The examiner assesses the level of detail, and GCSE content drags you down even if it is accurate. Every paragraph should contain terminology and detail that a GCSE student would not know.

4. No structure

An essay that jumps randomly between topics, circles back, or reads as a stream of consciousness is a Level 2–3 essay. Level 4–5 requires a logical structure where each paragraph builds on the last. This is why the 5-minute plan is so important.

5. No beyond-spec material

Without it, you cannot reach Level 5. Many students score a solid Level 4 (16–20 marks) and wonder why they did not hit 21+. The answer is almost always the absence of beyond-spec content.

Past Essay Titles and Themes

Understanding the pattern of past titles helps you prepare. Most follow one of two formats:

• “The importance of [concept] in living organisms” — for example, the importance of water, shapes, cycles, transport, energy transfers
• “How [structure/process] is related to [function]” — for example, how the structure of proteins relates to their functions

Common themes that have appeared repeatedly since 2017 include: shapes fitting together, cycles in biology, the importance of water, the role of proteins, variation and its biological importance, energy transfers, movement and transport, responses to stimuli, and the role of DNA and gene expression.

You should practise planning essays for a range of these themes. You do not need to write a full essay every time — writing detailed plans (5 topics, key terms, AO1/AO2 for each) is highly effective practice and takes only 10–15 minutes per title.

For links to official AQA past papers and mark schemes, see my AQA A-Level Biology page or visit the resources hub.

The Bottom Line

The 25-mark essay is not about writing everything you know. It is about selecting relevant content from across the specification, structuring it logically, and linking every paragraph explicitly to the essay title. Get the AO1/AO2 split right, cover at least five topic areas, and include one beyond-spec example, and you are looking at Level 5.

If you are an AQA student and want help with essay technique — including practice essays with detailed examiner-style feedback — I offer one-to-one online tuition and small group sessions. You can also book a free 20-minute consultation to discuss your preparation.

Tyrone John

Chartered Biologist (CBiol MRSB) • Former WJEC/Eduqas & Edexcel Examiner

Tyrone taught AQA Biology for 5 years at Gower College Swansea before switching to WJEC for the remaining 13 years. He has examining experience with WJEC/Eduqas and Edexcel, giving him insight into levels-based marking across multiple boards. He now provides specialist online tuition to AQA students across the UK.

Learn more about Tyrone →

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