Syllabus Edition

First teaching 2023

First exams 2025

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Barriers to Pathogens: Skin & Mucous Membranes (SL IB Biology)

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Skin as a Barrier to Pathogens

  • The skin and mucous membranes form a primary defence against pathogens that cause infectious disease
  • Skin is the largest organ of the body and is covered in microorganisms that usually cause no issues, as they can't enter the body. Skin provides:
    • A tough physical barrier that prevents entry of pathogens into our bodies
    • Cuts in the skin are sealed by formation of blood clots to prevent entry of pathogens
    • Chemical protection through the production of sebum from the sebaceous glands of the hair follicles
      • Sebum is a chemical responsible for maintaining a low skin pH which inhibits the growth of microorganisms
  • Mucous membranes are found lining vulnerable areas which may be a route for pathogens into the body
    • This includes the airways, areas around the reproductive organs (foreskin and vagina) and the digestive system
  • The membranes contain goblet cells which produce mucus containing glycoproteins
    • Microorganisms and particles become trapped by the mucus
    • The mucus is then swept along by the cilia of the ciliated epithelium upwards and is swallowed
    • The mucus and any microorganisms will then be swallowed and destroyed by the acid in the stomach or expelled, therefore preventing infection
    • Mucus also contains lysozyme enzymes which have antibacterial properties, providing more protection from invading microorganisms

Cilia and Goblet Cells Diagram

Ciliated Epithelium

Ciliated epithelium contains cilia, a basement membrane, and goblet cells

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Ruth

Author: Ruth

Expertise: Biology

Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. She gained 10 years of teaching experience across the 3 key science disciplines and physical education. Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.