Understanding Infection and Response in GCSE Biology

Pathogens and Disease Transmission

Pathogens are microorganisms that can cause disease in living organisms. There are different types of pathogens, including:

• Bacteria: Single-celled microorganisms that can reproduce rapidly and cause diseases like tuberculosis, cholera, and pneumonia.
• Viruses: Non-living particles that hijack host cells to replicate, causing diseases like influenza, HIV/AIDS, and COVID-19.
• Fungi: Multicellular organisms that can cause infections like athlete's foot, ringworm, and systemic infections in immunocompromised individuals.
• Protists: Single-celled eukaryotic organisms, such as the malarial parasite Plasmodium, which can cause serious diseases.

Pathogens can be transmitted through various routes, including:

• Direct contact with infected individuals or surfaces
• Airborne droplets from coughing or sneezing
• Contaminated food or water
• Insect vectors like mosquitoes

Body's Defence Mechanisms

The human body has several defence mechanisms to protect against pathogens:

Physical Barriers

• Skin: Acts as a physical barrier and produces antimicrobial substances.
• Mucous membranes: Trap pathogens and contain antimicrobial enzymes.
• Stomach acid: Kills many ingested pathogens.

Immune System

The immune system involves a coordinated response by different types of white blood cells:

• Phagocytes (e.g., neutrophils, macrophages) engulf and destroy pathogens through phagocytosis.
• Lymphocytes (e.g., B cells, T cells) produce antibodies and coordinate the immune response.

Memory cells provide long-term immunity by recognizing and responding quickly to previously encountered pathogens.

Antibody Production

1. Pathogens enter the body and are recognized as foreign.
2. B cells produce antibodies specific to the pathogen.
3. Antibodies bind to pathogens, marking them for destruction.
4. Memory B cells remain, providing long-term immunity.

Vaccination and Antibiotic Resistance

Vaccinations expose the body to weakened or inactive forms of pathogens, triggering an immune response and memory cell production without causing illness. This provides long-term protection against future infections.

Antibiotics are drugs used to treat bacterial infections, but their overuse has led to the development of antibiotic resistance, where bacteria evolve mechanisms to survive antibiotic exposure. This poses a significant challenge in treating bacterial infections.

Plant Diseases

Plants are also susceptible to pathogens, including fungi, bacteria, and viruses. Plant diseases can have devastating effects on crop yields and food production, leading to economic and social impacts. Understanding and managing plant diseases is crucial for sustainable agriculture.

For additional resources and support, visit BBC Bitesize: Infection and Response and refer to the official exam board specifications from AQA, OCR, Edexcel, and WJEC.