A-Level Biology long answers and extended writing: how to score full marks

Where long answers appear

Older Cambridge 9700 papers, set on earlier syllabuses, included an essay section. Practise from papers that match your current syllabus.

The key ideas

Start with the command word. 'Describe' means say what happens or what the data shows. 'Explain' means give reasons, using biological mechanisms. 'Compare' means similarities and differences, with both organisms or processes named in each point. 'Suggest' means apply knowledge to an unfamiliar situation; any reasonable, biologically correct answer can score. 'Evaluate' means weigh evidence for and against.

Count the marks and plan that many distinct points, plus one or two spare. A 6-mark answer needs at least six separate correct ideas. Each point should use the specific term from the specification, such as 'complementary base pairing', 'active site', 'water potential gradient' or 'hydrogen bonds', because mark schemes credit precise terms and reject vague ones such as 'it gets used'.

Order matters. Write a sequence for processes (transcription before translation), and link cause to effect with 'so' or 'therefore'. In data questions, quote figures with units and describe the trend before explaining it.

Worked example 1: 'Explain how a change in the base sequence of DNA can result in a non-functional enzyme.' (6 marks)

1. Plan the chain: DNA base sequence, mRNA, amino acid sequence, folding, active site, substrate binding.
2. A gene mutation such as a substitution, insertion or deletion changes the base sequence (triplets) of the gene.
3. During transcription this produces mRNA with one or more changed codons.
4. An insertion or deletion causes a frameshift, changing every codon after it; a substitution may change one amino acid or create a stop codon.
5. The primary structure (amino acid sequence) of the polypeptide changes.
6. This changes the bonds between R groups (hydrogen, ionic, disulfide), so the polypeptide folds into a different tertiary structure.
7. The active site changes shape, so it is no longer complementary to the substrate; no enzyme-substrate complexes form and the enzyme is non-functional. (A substitution can also be silent because the code is degenerate, which is worth stating.)

Worked example 2: 'Compare facilitated diffusion and active transport.' (4 marks)

1. Both use membrane proteins (carrier proteins; facilitated diffusion can also use channel proteins).
2. Facilitated diffusion moves substances down a concentration gradient; active transport moves them against it.
3. Facilitated diffusion is passive and does not use ATP; active transport uses ATP from respiration.
4. Active transport can accumulate a substance inside a cell; facilitated diffusion stops at equilibrium.
5. Each point names both processes, which is what 'compare' requires. Two separate descriptions without comparison usually score fewer marks.

Common mistakes that cost marks

• Describing when the question says explain, so no reasons are given.
• Vague terms: 'the enzyme dies', 'water moves to where there is less water', 'energy is made'.
• Repeating the question's words instead of adding new points.
• Writing fewer distinct points than the marks available.
• In comparisons, writing two separate paragraphs instead of matched points.
• Ignoring the data or context given in the question stem.

Exam technique and how a tutor helps

Spend 30 seconds planning a long answer as a list of keywords in the margin, then cross them off as you write. Use short sentences, one idea each. For Edexcel WBI15, read the pre-released article several times before the exam, look up unfamiliar terms, and link its content to specification topics.

Writing long answers improves fastest with feedback on real attempts. In one-to-one lessons the student writes an answer under timed conditions, and the tutor marks it against the official mark scheme, showing which sentences earned a mark and which were too vague. Repeating this with past-paper questions from the student's own board is the most direct way to raise marks on these questions.

Self-check: can you do these?

• What is the difference between 'describe' and 'explain'? (Answer: describe says what happens; explain says why)
• How many distinct points should a 5-mark answer have? (Answer: at least five)
• Rewrite 'the enzyme dies' in mark-scheme language. (Answer: the enzyme is denatured; its active site changes shape)
• Name one Cambridge 9700 paper that uses extended structured writing. (Answer: Paper 5)
• Which Edexcel IAL unit paper has a pre-released article? (Answer: Unit 5, WBI15)