Disease and immunity
Pathogens cause disease and spread by direct contact (blood, body fluids) or indirectly (air, water, food, vectors). The body's defences: skin, mucus and cilia, stomach acid, then white blood cells. Each pathogen carries antigens; lymphocytes make antibodies with complementary shapes that bind to them, marking pathogens for destruction. Memory cells remain, giving active immunity: a second infection is fought off faster and stronger. Vaccines contain harmless antigens to trigger this. Passive immunity (antibodies from breast milk or injection) is short-lived.
≈ 40 minMedicinal and misused drugs
A drug is any substance taken into the body that changes its chemical reactions. Antibiotics kill or stop the growth of bacteria but have no effect on viruses. Overuse leads to antibiotic resistance: random mutations make some bacteria resistant; they survive and multiply (natural selection), e.g. MRSA. Reduce it by prescribing antibiotics only when needed and finishing the course. Misused drugs harm the body: alcohol (depressant, liver damage), heroin (depressant, highly addictive, infection from shared needles), nicotine (addictive), anabolic steroids (muscle growth, banned in sport).
≈ 30 min