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TL;DR Paper 3 Section B gives you a choice of two essays worth 25 marks each. Most students lose marks not because they lack content knowledge but because they write vaguely, ignore the question scope, or fail to include enough named examples. This guide gives you a repeatable paragraph framework, a bank of high-value named examples, and a question-type playbook so you can consistently hit 20/25.
Paper 3 Section B is the only part of the H2 Biology A-Level examination where you write in continuous prose without guided sub-parts. That freedom is both an opportunity and a trap: examiners can reward breadth of knowledge and scientific communication, but they can also penalise waffle, imprecision, and off-topic material with equal efficiency.
Point-based with a quality of written communication (QWC) band descriptor
Syllabus scope
Any Core Idea or Extension Topic may be tested; cross-topic essays are common
Section B essays are marked using a two-tier system. Content marks reward individual scientific points (typically 20 marking points available, of which 20 maximum are awarded). The remaining marks come from QWC descriptors that assess coherence, use of scientific terminology, and logical flow. You need both accurate content and clear communication to reach the top band.
Content accuracy. Every factual claim must be scientifically correct. A single teleological statement (e.g. "the enzyme wants to bind the substrate") can cost a mark and flag your essay as lacking rigour.
Scientific vocabulary. Use precise terms from the syllabus. Write "hydrolysis" not "breaking down", "complementary base pairing" not "matching bases", and "phosphodiester bonds" not "connections between nucleotides".
Breadth of examples. Top-band essays draw from multiple syllabus areas. An essay on "the importance of proteins" should span enzymes, antibodies, structural proteins, channel proteins, and hormones rather than spending five paragraphs on enzyme kinetics alone.
Coherence and logical flow. Paragraphs should follow a logical sequence. Each paragraph should connect to the question and transition smoothly to the next.
3 Essay structure template
A reliable essay structure for a 25-mark Section B question:
Opening paragraph (2--3 sentences)
Define the key term in the question. State the scope of your answer. Signal the range of biological levels or syllabus areas you will cover.
Example: "Enzymes are globular proteins that function as biological catalysts, lowering the activation energy of metabolic reactions. Their importance extends from intracellular metabolism to extracellular digestion, signal transduction, and DNA replication."
Body paragraphs (4--5 paragraphs)
Each paragraph covers one distinct biological context or syllabus area. See the paragraph framework in Section 5 below.
Closing paragraph (1--2 sentences)
Briefly tie the essay back to the question. Do not introduce new content. A simple restatement that synthesises the breadth of your answer is sufficient.
Example: "Collectively, the roles of enzymes in catalysis, regulation, and cellular signalling illustrate that protein function is central to virtually every biological process."
4 How to unpack the question
Before writing a single sentence, spend two minutes analysing the question. Identify three things:
Scope
What biological concept or molecule is the question about? Does it restrict you to a particular context (e.g. "in mammals" or "at the molecular level")? Ignoring scope constraints is one of the most common reasons students write off-topic paragraphs that earn zero marks.
Biological level
Is the question asking about molecular, cellular, tissue, organism, or population-level phenomena? Some questions span multiple levels; if so, plan your paragraphs to move systematically from small scale to large scale (or vice versa).
Command word
Command word
What it requires
Describe
State what happens, step by step
Explain
State what happens and give reasons (mechanism + cause)
Discuss
Present multiple perspectives or examples, often with evaluation
Compare
Identify similarities and differences in parallel structure
Outline
Give a brief account of the main points without full detail
"Discuss" is the most common command word in Section B. It requires breadth and some evaluative commentary, not just a list of facts.
5 Paragraph structure framework — TEMS
Use the TEMS framework for every body paragraph:
T — Topic sentence. State the point this paragraph will make and connect it to the question.
E — Example (named). Provide a specific, named biological example.
M — Mechanism. Explain the underlying process, pathway, or structural basis.
S — Significance. Explain why this matters in the context of the question.
Worked example
Question: "Discuss the importance of membrane proteins in living organisms."
T: Membrane transport proteins are essential for the selective movement of ions and polar molecules across the phospholipid bilayer. E: The sodium-potassium pump (Na+/K+-ATPase) in animal cell membranes actively transports 3 Na+ ions out and 2 K+ ions into the cell per cycle of ATP hydrolysis. M: This pump undergoes conformational changes upon phosphorylation, alternating between states that expose ion-binding sites to the cytoplasm and the extracellular fluid. The resulting electrochemical gradient is maintained by continuous ATP expenditure. S: The Na+/K+ gradient established by this pump is critical for maintaining resting membrane potential in neurones, driving secondary active transport of glucose in the small intestine, and regulating cell volume through osmotic balance.
Each TEMS paragraph should be 80--120 words. Aim for five such paragraphs to maximise content marks.
6 Breadth vs depth: which strategy scores higher?
This is one of the most common strategic questions students ask. The answer, based on how the mark scheme is structured, is clear: breadth wins.
Paper 3 mark schemes typically list 20 or more marking points, of which you need to hit around 16--18 to reach the top content band. Each marking point usually corresponds to a distinct biological context or example. Writing three paragraphs of deep mechanistic detail on one topic might earn you 6--8 marks. Writing five paragraphs that each cover a different context can earn 15--18 marks.
The practical strategy:
Plan five distinct contexts before you start writing.
Give each context one TEMS paragraph (100 words).
Add depth only if you finish early during the review phase.
This does not mean your paragraphs should be shallow. Each paragraph must include a named example and a correct mechanism. The point is to resist the temptation to write everything you know about one topic at the expense of covering others.
7 Common question types and how to approach each
Type 1: "Discuss the importance of X in living organisms"
This is the classic breadth question. X is usually a molecule (proteins, lipids, water), a process (mitosis, respiration), or a structural feature (membranes, hydrogen bonds).
Approach: Plan 5--6 different roles or contexts. Each body paragraph covers one role with a named example. Move across biological levels (molecular, cellular, organism, ecological) to demonstrate range.
Type 2: "Describe how X is maintained"
This tests your knowledge of regulatory mechanisms: homeostasis, gene expression control, or feedback loops.
Approach: Identify 3--4 mechanisms that contribute to maintaining X. For each mechanism, describe the stimulus, the receptor, the effector, and the response. Use specific named examples (e.g. baroreceptors in blood pressure regulation, insulin and glucagon in blood glucose homeostasis).
Type 3: "Compare X and Y"
Comparison questions require parallel structure. Every point you make about X must have a corresponding point about Y.
Approach: Draw a quick comparison table during planning. Organise paragraphs by feature (e.g. structure, function, location, regulation) rather than writing everything about X first and then everything about Y. Integrated comparison paragraph by paragraph earns more marks than a split "X then Y" structure.
Type 4: "Explain how changes in X affect Y"
This tests cause-and-effect reasoning and is common for topics involving regulation, mutation, or environmental change.
Approach: Build a causal chain for each paragraph. State the change in X, identify the immediate molecular or cellular consequence, trace the effect through intermediate steps, and arrive at the impact on Y. Be explicit about each link in the chain — examiners cannot award marks for implied reasoning.
8 Named examples bank
The following 20 named examples are high-value because each one can be deployed across multiple essay types. Memorise the example, the mechanism, and at least two contexts in which it is relevant.
No.
Named example
Key mechanism
Applicable essay topics
1
Haemoglobin
Cooperative binding, quaternary structure, allosteric regulation by CO2/H+ (Bohr effect)
Proteins, gas transport, allosteric regulation
2
Na+/K+-ATPase
Active transport, conformational change, ATP hydrolysis
Membrane proteins, nerve impulse, active transport
Phosphorylation of target proteins, cell cycle progression
Cell cycle, enzymes, cancer
20
Sickle cell haemoglobin (HbS)
Point mutation (Glu to Val), hydrophobic interaction, polymerisation
Mutations, natural selection, protein structure
9 Time management for the essay
You have approximately 45 minutes for Section B. Divide that time deliberately:
Phase
Time
What to do
Planning
5 minutes
Read both questions. Choose one. List 5--6 contexts/examples. Sketch a brief paragraph plan.
Writing
35 minutes
Write 5 TEMS paragraphs plus an opening and closing paragraph. Aim for 600--700 words total.
Review
5 minutes
Check for scientific accuracy, missing key terms, and unanswered parts of the question. Add any quick additional points in the margin if needed.
Planning is non-negotiable. Students who skip the planning phase almost always write essays that drift off-topic or repeat the same point in multiple paragraphs. Five minutes of planning typically adds 3--5 marks to the final score.
10 Common mistakes and how to avoid them
Vague language
"The protein helps the cell" earns nothing. "The channel protein facilitates the diffusion of potassium ions down their concentration gradient across the plasma membrane" earns marks. Every sentence should contain at least one specific scientific term.
Teleological explanations
Saying "the enzyme changes shape so that it can bind the substrate better" implies purpose or intention. Correct phrasing: "the enzyme undergoes a conformational change upon substrate binding, resulting in a more precise fit (induced fit model)."
Forgetting named examples
A paragraph without a named example is a paragraph that earns fewer marks. The mark scheme explicitly awards points for specific named molecules, organisms, or processes. Generic descriptions without names rarely earn full credit.
Ignoring question scope
If the question says "at the molecular level", do not write about whole-organism physiology. If the question says "in plants", do not spend three paragraphs on animal examples. Read the question twice during planning and once more during review.
Writing a narrative instead of making points
Some students write flowing prose that reads well but buries the marking points. Examiners scan for specific scientific statements. Make each point clearly and explicitly, even if the prose style feels more direct than literary.
Unbalanced coverage
Spending half the essay on one topic and rushing through three others in a single paragraph is a common pattern. Your paragraph plan should allocate roughly equal word count to each context.
11 Frequently asked questions
How long should my essay be?
Aim for 600--700 words, or roughly 2.5 to 3 pages of average-sized handwriting. Quality matters more than length, but essays shorter than 500 words rarely cover enough marking points for a top-band score.
Should I use diagrams in my essay?
You may include small, clearly labelled diagrams if they genuinely support a point (e.g. a simple diagram of antibody structure when discussing variable regions). However, diagrams do not replace written explanation. The mark scheme is based on written scientific statements, and examiners will not award marks for a diagram alone without accompanying text.
How do I choose between the two essay questions?
Spend the first two minutes of your planning phase reading both questions carefully. Choose the question where you can identify at least five distinct contexts or examples immediately. Avoid choosing a question just because the topic sounds familiar — if you can only think of two or three points, you will struggle to reach the top band.
Do I need to memorise essay plans?
Memorising rigid essay plans for predicted topics is risky because questions can combine topics in unexpected ways. Instead, memorise a bank of named examples (see Section 8) and practise applying the TEMS framework to past-year and specimen questions. Flexibility with a strong framework beats a memorised script.
Can I use bullet points instead of continuous prose?
No. Section B explicitly requires continuous prose. Using bullet points or numbered lists will lower your QWC band and may result in content marks not being awarded even if the scientific content is correct.
How many past-year essay questions should I practise?
Aim to write at least 8--10 full timed essays before the examination. Focus on variety — cover different question types and syllabus areas. After writing each essay, compare your content against the mark scheme and identify gaps in your named examples or mechanisms.
