Overview: Paper 3 Essay (25 marks)
- You are given a choice of two titles to write a detailed essay that draws on knowledge and understanding from across the entire specification.
- 25 marks are split between:
- 13 marks for AO1: Demonstrate knowledge and understanding of scientific ideas, processes, techniques and procedures
- 12 marks for AO2: Apply knowledge and understanding of scientific ideas, processes, techniques and procedures
Overall Tips
- Include at least 4 different topics from across the specification (You can cover 5 topics if you have time)
- Link each topic back to the theme of the essay
- Use detailed, A-level explanations (not GCSE level content) with specific examples
- Be careful NOT to include biology inaccuries or irrelevant material (i.e content that is not related to the title), as these will lose marks
- An introduction or conclusion isn’t required, so you don’t need to spend time on this
- To achieve 24/25 marks, you need to include material beyond the specification. This needs to be relevant, correct, and at least an A-level standard.
Example Essay Template
Planning (~5-10 mins)
- Select 4–5 topics from different areas of the course that are relevant to that concept
- For each topic write 2-3 bullet points, explaining the key points you want to cover in the essay.
- It can be helpful to structure bullets as AO1 (knowledge) and AO2 (why it’s important). Examiner reports often state that students can write excellent descriptions (AO1) but fail to explain the importance (AO2).
Writing (~40 mins)
- Aim to write 4-5 paragraphs, one per topic
- Each paragraph could have the following included:
- Introduce your topic and ensure it refers to the title directly
- Detailed description & explanation of the topic, using accurate terminology and providing specific examples (AO1)
- Explain why this topic is important and ensure you link it back to the essay theme (AO2)
- This includes thinking about:
- Why is this topic important?
- What would be the consequences or impact without it?
- This includes thinking about:
Always link back to the title
It is easy to write a lot about a topic without actually answering the question. Always think about linking and explaining why the concept is important in the context of the essay theme — not just what it is or how it works.
Example: Essay Planning
The plan below shows how you could approach the title. Note: There are many different topics you could have chosen — this is just a selection.
Each topic has an AO1 point(knowledge) and an AO2 point (application/importance), with the spec references shown.
Phosphorus-containing substances and their importance in biological systems
ATP (3.1.6)
- AO1: Structure ATP & ATP hydrolysis. Hydrolysis of ATP can be coupled to energy-requiring reactions within cells.
- AO2: Important for energy requiring reactions: muscle contraction (e.g detaching myosin heads), active transport (e.g sodium-potassium pump)
DNA and RNA (3.1.5.1 & 3.4.2)
- AO1: Structure of DNA and RNA (nucleotides /phosphodiester bonds). DNA/RNA role in transcription & translation
- AO2: Importance of accurate transcription & translation for protein synthesis.
- DNA coding > primary structure. This determines secondary & tertiary protein structure.
NAD - Respiration (3.5.2)
- AO1: NAD’s role in respiration
- Reduced in glycolysis and the Krebs cycle
- Oxidised in oxidative phosphorylation.
- AO2: Importance for chemiosmosis & ATP generation
NADP - Photosynthesis (3.5.1)
- AO1: NADP’s role in photosynthesis
- Light-dependent reaction becoming reduced (NADP → NADPH)
- Reduced NADP then donates hydrogen to reduce GP to triose phosphate in the Calvin cycle
- AO2: Importance of NADP in the light-independent reactions and for the plant producing glucose.
cAMP Control of Blood Glucose (3.6.4.2)
- AO1: Cyclic AMP is a phosphorus-containing second messenger
- Glucagon/adrenaline bind to receptors, activating adenyl cyclase which converts ATP to cAMP
- cAMP activates protein kinase, triggering glycogen breakdown
- AO2: Important for glycogenolysis / raising blood glucose levels (control of blood glucose)
Examiner tips from examiner report summarised
Examiner tips from examiner report summarised
- Choose different phosphorus-containing substances for each paragraph — writing only about ATP across multiple topics effectively makes the essay “ATP and its importance”
- Proteins and enzymes are not phosphorus-containing substances — including a paragraph on either is a significant biological error and will be marked as irrelevant
- The AO2 “importance” aspect is most commonly missed out. It’s important to go beyond describing the process and explain why the phosphorus-containing substance is important. E.g Students gave good AO1 descriptions on how DNA and RNA are involved in transcription and translation, but chose to write about protein structure instead of outlining how and why DNA and RNA are important in protein synthesis.
- Not every bond is a hydrogen bond — be precise about bond types (phosphodiester, glycosidic, peptide, etc.)
- ATP hydrolysis does not power every aspect of muscle contraction — be specific about which steps require ATP