AQA GCSE FOUNDATION Biology: Human Defense Mechanisms

AQA GCSE Foundation Biology: Human Defence Mechanisms

This tutorial will cover the human body's incredible defence mechanisms against pathogens.

What are pathogens?

Pathogens are disease-causing organisms like bacteria, viruses, fungi, and parasites. They can enter our bodies through various ways, such as:

• Inhalation: Breathing in airborne pathogens.
• Ingestion: Eating or drinking contaminated food or water.
• Direct contact: Touching infected surfaces or individuals.
• Animal bites: Infected animal bites can introduce pathogens.

The Body's First Line of Defence: Physical Barriers

Our bodies have a first line of defence against pathogens:

• Skin: The skin acts as a barrier, preventing most pathogens from entering the body. It also secretes oils and sweat, which have antibacterial properties.
• Mucus: Mucus lines the respiratory and digestive tracts, trapping pathogens and preventing them from reaching our lungs and stomach.
• Cilia: Tiny hair-like structures in the respiratory tract that sweep mucus and trapped pathogens upwards, towards the throat, where they can be swallowed or coughed out.
• Stomach acid: The stomach produces highly acidic gastric juices that kill many pathogens.
• Tears: Tears contain an enzyme called lysozyme, which breaks down bacterial cell walls.

The Body's Second Line of Defence: Immune Response

If pathogens manage to bypass the first line of defence, our bodies trigger an immune response. This involves:

• White blood cells: These cells are crucial in fighting infection. Different types of white blood cells have specific roles:

  • Phagocytes: These cells engulf and destroy pathogens by a process called phagocytosis.
  • Lymphocytes: These cells recognize specific pathogens and produce antibodies or directly attack infected cells.

• Inflammation: This is a localized response to infection, characterized by redness, swelling, heat, and pain. Inflammation helps to isolate the infection and attract white blood cells to the site of infection.

Antibodies

Antibodies are Y-shaped proteins produced by lymphocytes that specifically bind to antigens (molecules on the surface of pathogens). This binding:

• Neutralizes: Prevents the pathogen from entering cells.
• Agglutination: Clumps pathogens together, making them easier for phagocytes to engulf.
• Opsonisation: Coats the pathogen, making it easier for phagocytes to recognize and engulf it.

Vaccination

Vaccination is a crucial way to protect against infectious diseases. Vaccines introduce a weakened or inactive form of a pathogen into the body, triggering an immune response. This allows the body to produce antibodies without experiencing the disease.

Key Concepts:

• Pathogen: A disease-causing organism.
• First line of defence: Physical barriers like skin, mucus, and stomach acid.
• Second line of defence: Immune response involving white blood cells and inflammation.
• Phagocytosis: Process of engulfing and destroying pathogens.
• Antibodies: Y-shaped proteins that bind to antigens and neutralize pathogens.
• Vaccination: Introducing weakened or inactive pathogens to trigger an immune response.

Conclusion

Our bodies have a complex and efficient system of defences against pathogens. By understanding these mechanisms, we can appreciate the remarkable ability of our bodies to combat disease and protect us from harm.