Revision notes · Biology
Communicable diseases are caused by pathogens: bacteria (produce toxins), viruses (invade and destroy cells), fungi, and protists.
The body's first line of defence (non-specific): skin (barrier), mucus and cilia (trap and sweep), stomach acid (kills pathogens), tears/saliva (contain lysozyme).
If pathogens enter: white blood cells respond via phagocytosis (engulfing), antibody production (specific to antigens), and antitoxin production.
Vaccination: dead/inactive pathogen injected → white blood cells produce antibodies and memory cells → rapid response if real pathogen encountered.
Antibiotics kill bacteria but NOT viruses. Antibiotic resistance occurs when bacteria evolve to survive antibiotics (e.g. MRSA).