Pathogens & Barriers | Biology for GCSE/IGCSE - Year 11 PDF Download

Pathogens

• A pathogen is a microorganism that causes diseases. These harmful organisms are responsible for various illnesses in living beings.
• Pathogens are transmitted from one host to another, leading to what are known as communicable diseases.
• Different modes of pathogen transmission exist, such as:
  • Direct contact: Where pathogens are transferred directly from one individual to another through body fluids like blood or semen. For instance, diseases like HIV, gonorrhea, and hepatitis B & C are transmitted this way.
  • Indirect contact: Where the pathogen leaves one host and is transported to another uninfected individual through various means.

Methods of Transmission Table

The Body Defenses

Our body has three primary defense mechanisms against diseases:

• Mechanical barriers: These are protective structures that hinder pathogens from entering the body.
  • Skin: Acting as a physical barrier, the skin covers most of the body, preventing pathogen entry. When damaged, it heals itself, often by forming a scab.
  • Hairs in the nose: These tiny hairs obstruct pathogens from entering deeper into the nose to avoid inhalation into the lungs.
• Chemical barriers: These are substances produced by body cells that trap or kill pathogens before they can cause diseases.
  • Mucus: Generated in various body parts, mucus traps pathogens, facilitating their removal from the body through actions like coughing, blowing the nose, or swallowing.
  • Stomach acid: With hydrochloric acid, the stomach acid is potent enough to eliminate pathogens trapped in mucus in the airways, whether swallowed or ingested through food or water.
• Cells: Different types of white blood cells work to prevent pathogens from reaching areas of the body where they can replicate.
  • Phagocytosis: This process involves white blood cells engulfing and digesting pathogenic cells.
  • Antibody Production: White blood cells produce antibodies that clump pathogenic cells together (agglutination), making it harder for them to move. They also release chemicals that signal other cells to destroy the pathogens.