IB Biology SL

Revision Notes

6.3.1 Skin


  • 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 and are then either swallowed (into the stomach) or expelled, therefore preventing infection
    • Mucus also contains lysozyme enzymes which have antibacterial properties, providing more protection from invading microorganisms

Author: Ruth

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. With 10 years of teaching experience across the 3 key science disciplines, 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.

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