Understanding Infection and Response in GCSE Biology

Pathogens and Disease Transmission

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

• Bacteria: Single-celled organisms lacking a true nucleus, such as Salmonella and Staphylococcus aureus.
• Viruses: Non-living particles that hijack host cells to replicate, like the influenza virus.
• Fungi: Eukaryotic organisms that include yeasts and moulds, some of which can cause skin infections.
• Protists: Single-celled eukaryotes like the malaria parasite Plasmodium.

Pathogens can be transmitted through direct contact, bodily fluids, airborne particles, contaminated food/water, and insect vectors.

Body Defences and Immune Response

The body has several lines of defence against pathogens:

1. Physical Barriers: Skin, mucus membranes, stomach acid, and cilia act as the first line of defence.
2. White Blood Cells: If pathogens breach the physical barriers, white blood cells respond:
• Phagocytes (e.g., neutrophils, macrophages) engulf and digest pathogens through phagocytosis.
• Lymphocytes produce antibodies that bind to and neutralise specific pathogens.
3. Memory Cells: After an initial exposure, memory cells allow a faster and stronger immune response upon subsequent encounters with the same pathogen.

Vaccination and Disease Prevention

Vaccines expose the body to weakened or inactive forms of a pathogen, prompting the immune system to create memory cells. This provides future protection against the disease. Other prevention methods include:

• Developing new antibiotics and antiviral drugs
• Improved sanitation and food/water safety
• Controlling insect vectors that spread pathogens

Antibiotic Resistance

Overuse of antibiotics can lead to the evolution of resistant bacterial strains, making infections harder to treat. This highlights the importance of responsible antibiotic use and developing new drugs.

Plant Diseases

Plants can also be affected by pathogens like fungi, bacteria, and viruses. Plant diseases can have significant economic impacts on agriculture and food production.