First line of defence

• Pathogens produce toxins which makes a person sick
• Skin

  Covers the body and protects against physical damage, dehydration, and microbial infection

  Microbes cannot penetrate the skin's dry dead outer cells
• Tears

  Contain lysozyme (enzyme) which breaks down the cell wall of many bacteria, killing them
• Stomach acid

  Exposure to a high level of acidity kills bacteria because they use enzymes to get nutrients

  When exposed to acid, enzymes denature and the bacteria runs out of nutrients
• Mucus is secreted by specialised epithelial cells line the nasal cavity and trachea. Mucus is sticky and traps pathogens

  The epithelial cells also have cilia which move in a wave like motion to move mucus out of the lungs and trachea