Understanding Infection and Response in GCSE Biology

Types of Pathogens

Pathogens are microorganisms that can cause disease in humans and other living organisms. The main types of pathogens include:

• Bacteria: Single-celled organisms that can be beneficial or harmful. Examples: Salmonella, Staphylococcus.
• Viruses: Non-living particles that rely on host cells to replicate. Examples: Influenza, COVID-19.
• Fungi: Multicellular organisms that include yeasts and molds. Examples: Candida, ringworm.
• Protists: Single-celled eukaryotic organisms. Examples: Plasmodium (malaria), Entamoeba (dysentery).

How Pathogens Cause Disease

Pathogens can cause disease in various ways, including:

• Producing toxins that damage cells or interfere with normal bodily functions.
• Invading and destroying host cells or tissues.
• Disrupting the normal functioning of the body's systems.

Transmission of Pathogens

Pathogens can be transmitted through different routes, such as:

• Direct contact with an infected person or their body fluids.
• Indirect contact through contaminated surfaces, objects, or food.
• Airborne transmission via coughing, sneezing, or other respiratory droplets.
• Vector transmission by organisms like mosquitoes or ticks.

The Body's Defence Mechanisms

The human body has several lines of defence against pathogens:

1. Physical barriers: Skin, mucous membranes, and stomach acid act as the first line of defence.
2. Non-specific immune response: White blood cells (leukocytes) like phagocytes engulf and destroy pathogens.
3. Specific immune response: Lymphocytes (B-cells and T-cells) produce antibodies and memory cells for targeted immunity.

Phagocytosis

Phagocytes (e.g., neutrophils and macrophages) are white blood cells that engulf and destroy pathogens through phagocytosis:

1. The phagocyte engulfs the pathogen, forming a phagosome.
2. The phagosome fuses with lysosomes, releasing enzymes that break down the pathogen.
3. The digested pathogen is removed from the cell.

Vaccination and Disease Prevention

Vaccines stimulate the immune system to produce antibodies and memory cells against specific pathogens, providing long-lasting protection:

• Inactivated or weakened forms of pathogens are introduced, triggering an immune response.
• Memory cells remain in the body, ready to mount a rapid response if exposed to the same pathogen.

Other disease prevention strategies include:

• Developing new antibiotics and antiviral drugs.
• Addressing antibiotic resistance through responsible use and developing new antibiotics.
• Public health measures like sanitation, hygiene, and vector control.