Exam Tips: Non-Specific Human Defences

State the barrier AND explain the mechanism: "Skin acts as a physical barrier" is one mark. "Skin acts as a physical barrier, preventing pathogens from entering underlying tissues" is two marks. Always link the structure to what it does.

Mucus and cilia work as a pair: Never describe one without the other. Mucus traps the pathogens; cilia move the mucus. Together they form the "ciliary escalator." If smoking destroys cilia, mucus cannot be swept away, increasing infection risk — a favourite exam application question.

Phagocytosis — three clear steps: (1) Phagocyte detects chemicals from the pathogen and moves towards it. (2) Phagocyte surrounds the pathogen with its cell membrane and engulfs it. (3) Enzymes inside the phagocyte digest and destroy the pathogen. Missing step 3 (the enzymes) is the most common mark loss.

Non-specific vs specific immunity distinction: Non-specific responds the same way to ANY pathogen; does not require previous exposure; does not produce memory. Specific (adaptive) immunity is tailored to one specific antigen, is slower on first exposure but faster on re-exposure, and creates memory cells. This distinction is tested frequently.

Required practical — use area not diameter for comparisons: The zone of inhibition is circular. Area = pi x r squared. This gives a more meaningful comparison than diameter alone. Higher-tier questions may ask you to calculate and compare areas from given diameter measurements.