Key facts & rules

• Pathogen types: bacteria (e.g. tuberculosis, Salmonella), viruses (e.g. influenza, HIV), fungi, protists (e.g. malaria).
• Transmission: direct contact, droplets, contaminated food/water, vectors (e.g. mosquitoes).
• Physical defences: skin, mucus, cilia (in trachea), stomach acid.
• Phagocytes: engulf and destroy pathogens (non-specific).
• Lymphocytes: produce specific antibodies that bind to antigens on pathogens.
• Memory cells: remain after infection → faster response if same pathogen returns (immunity).
• Vaccination: introduces antigens (dead/weakened/antigen only) → immune system produces antibodies + memory cells.
• Antibiotics: kill bacteria — NOT effective against viruses. Overuse causes antibiotic resistance.