International A Level Biology / Microbiology

How pathogens enter and how the body keeps them out

Edexcel International A Level Biology (YBI11), chapter 17: Microbiology, specification point 6.7. Part of the full course.

Read the revision notes · International A Level Biology past papers

Pathogens enter through thin or broken body surfaces, while non-specific barriers help stop them reaching tissues and multiplying. Knowing the difference between a pathogen and an infection, and explaining how each barrier works, helps you give precise exam answers.

More lessons in Microbiology

• Bacteria and viruses compared
• Lytic and latent infections
• The bacterial growth curve
• Calculating exponential growth and the growth rate constant
• Culturing microorganisms with aseptic technique
• Measuring growth: cell counts and dilution plating
• Measuring growth: turbidity and mass
• Core practical 13: growth of microorganisms in liquid culture
• Tuberculosis: how Mycobacterium tuberculosis causes disease
• HIV: how the virus infects and leads to AIDS