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 14 of 16 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Topic position
Section 14 of 16
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; standard questions ask for mechanistic explanations of phagocytosis.
- 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.
- 3-mark phagocytosis sequence: Must include all steps in order: detection (phagocyte detects chemicals from pathogen), engulfment (cell membrane surrounds pathogen), and digestion (enzymes break down the pathogen). 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.
- Mucus and cilia pair: Always describe both together. Mucus traps; cilia sweep. Smoking application: smoking damages cilia so mucus cannot be cleared, increasing infection risk.
Common mark losses: Saying mucus kills bacteria (it traps them; lysozyme kills them). Forgetting that cilia sweep mucus to the throat (not just "upwards"). Not stating what the enzymes do in phagocytosis (they break down/digest the pathogen).