This exam focus covers Exam Focus within Human Defense Systems - Non-specific for GCSE Biology. Physical and chemical barriers, white blood cell responses, inflammatory response It is section 16 of 18 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Topic position
Section 16 of 18
Practice
19 questions
Recall
22 flashcards
Exam Focus
Frequently ExaminedNon-specific defences are examined at all difficulty levels in AQA biology. Foundation questions test recall of barriers; higher questions ask for mechanistic explanations of phagocytosis and inflammation.
- 3-mark "describe how the body prevents pathogens entering" questions: Give three distinct points — skin as physical barrier, mucus trapping pathogens in airways, and stomach acid killing swallowed pathogens. Each needs to name the barrier AND explain how it prevents infection.
- 4-mark phagocytosis sequence: Must include all steps in order: recognition, attachment, engulfment (phagosome formation), lysosome fusion, enzyme digestion, waste expulsion. Missing any step loses marks.
- Required practical (disc diffusion): Know independent, dependent, and control variables. Know why 25°C is used. Know how to calculate zone area. Know what a water control shows.
- 6-mark extended response on inflammation: Structure your answer: stimulus (tissue damage/infection) → histamine release → vasodilation → increased blood flow → increased capillary permeability → white blood cells leave bloodstream → phagocytosis of pathogens. Include signs (redness, swelling, heat, pain) with causes.
Common mark losses: Saying mucus kills bacteria (it traps them; lysozyme kills them). Forgetting that macrophages present antigens (this links non-specific to specific immunity). Describing phagocytosis without mentioning lysosomes and enzymes.