2.6: Physical Barriers to Disease

Question 1

Role of the immune system

Answer 1

• The immune system is a complex network of organs, cells and proteins that defends the body from diseases and foreign substances
• Detects when a virus, bacteria or foreigns substance is in the body
• Causes scabs and blood to clot to prevent infection
• The immune system keeps a record of every germ (microbe) it has ever defeated so it can recognise and destroy the microbe quickly if it enters the body again.

Question 2

1st line of defence

Answer 2

• Physical barriers that prevent entry to pathogens. For example:
• Skin protects the internal organs
• Fluids such as tears and saliva
• Nose hairs to filter air
• Stomach acid usually kills pathogens that have entered the digestive system
• Vomiting and diarrhoea rapidly remove unwanted substances from the body

Question 3

Mechanical v Chemical Protection

Answer 3

• Mechanical: Blinking, is a reflex response when the eye is irritated by foreign particles
• Chemical: The cells in the eyes secrete enxymes called Lysozyme to chemically breakdown bacteria.

Question 4

Self v Non-self

Answer 4

• Foreign particles are identified by the body as ‘non-self’
• Body’s own molecules and surface receptors are identified as ‘self’
• A particle identified as ‘non-self’ will be removed by antibody production