Topic Summaries

Pathogens

IGCSE > Biology > Pearson IGCSE > IGCSE Biology Topic Summaries > Pathogens and non-specific immunity > Pathogens
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Stem cells, microscopy, and microorganisms

Pathogens and non-specific immunity

Plant disease and monoclonal antibodies

Resource cycles and environmental change

Science skills: Measuring results

  • Pathogens are microorganisms (viruses, bacteria, protists, and fungi) that cause infectious disease.
  • There are various ways a disease can be spread in animals and plants:
    • Direct contact: spread by physical contact
    • Transfer of infected fluids: e.g. blood, saliva, semen
    • Contaminated water: travels in unsterilised water
    • Airborne: propelled through the air in tiny droplets of water through sneezing and coughing
    • Food: pathogens in uncooked or spoiled food
    • Via another animal: the animal is called a vector
  • The spread of disease can be reduced or prevented by:
    • Sterilising water with chemicals or UV light
    • Cooking food thoroughly and preparing it in hygienic conditions
    • Disinfecting surfaces
    • Treating infections, e.g. with antibiotics
    • Vaccination
    • Barrier method of contraception to prevent the spread of sexually transmitted diseases, e.g. condoms
  • Bacteria and viruses can reproduce rapidly inside the body.
    • Bacteria can produce toxins that damage tissues and cause disease symptoms.
    • Viruses live and reproduce inside cells, causing cell damage.

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