Exam Focus

Exam Focus

Non-specific defences are examined at all difficulty levels. Edexcel 1BI0 Paper 1 (Topic 5: Health, Disease and Medicine) includes this content with stimulus-based questions — you may be given a scenario about a patient with a specific infection and asked to "Suggest" how the body would respond. Foundation questions test recall of barriers; standard questions ask for mechanistic explanations of phagocytosis. On Edexcel, 6-mark extended responses often require you to link the non-specific and specific immune responses.

• 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).