This exam focus covers Exam Focus within Gas Exchange in Humans for GCSE Biology. Lung structure, alveoli adaptations, breathing mechanism, gas transport in blood, and effects of smoking It is section 17 of 19 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Topic position
Section 17 of 19
Practice
19 questions
Recall
23 flashcards
Exam Focus
Very Frequently ExaminedGas exchange is one of the most heavily examined topics in AQA Unit 2. It has appeared in some form in virtually every exam series since 2017.
- 4-mark "explain the adaptations" questions: Almost always on alveoli. You must state each adaptation AND explain how it increases the rate of diffusion. Use the SLIM mnemonic to ensure you cover all four. Example: "The moist lining dissolves gases, which is necessary because diffusion can only occur across a liquid surface."
- 6-mark extended response: Often asks you to explain the entire gas exchange process or compare breathing and gas exchange. Structure your answer logically: structure of alveolus → concentration gradients → how each adaptation maintains the gradient.
- Breathing mechanism (4 marks): Describe what happens to diaphragm, intercostal muscles, chest volume, pressure, and air movement — in the correct sequence. Include the word "pressure" or you will lose marks.
- Disease application questions: Emphysema, asthma, and lung cancer are the three most common disease contexts. For each, the question tests whether you can link the structural damage to the loss of gas exchange efficiency.
- RPA5 (Photosynthesis) crossover: The same diffusion and surface area principles apply to gas exchange in leaves — be ready to connect these topics.
Common mark losses: Saying the diaphragm goes down during expiration. Saying "more oxygen is needed" as the reason breathing rate rises (the trigger is rising CO₂). Forgetting the moist lining as an alveolar adaptation.