Human defences

Question 1

Describe what a physical barrier is

Answer 1

something that makes it hard for pathogens to enter the body

Question 2

Describe what a chemical defence/barrier is

Answer 2

chemicals that are produced to kill or make pathogens inactive

Question 3

Name and describe 3 chemical defences

Answer 3

Tears: contain lysozyme enzymes that kill bacteria by digesting their cell walls

Saliva/mucus: also contain lysozyme enzyme

Stomach: hydrochloric acid (stomach acid) kills pathogens in food and drink

Question 4

Name and describe 3 physical barriers

Answer 4

Skin: when it is unbroken it forms a protective barrier because it is too thick for most pathogens to get through

Cilia/mucus: mucus in the breathing passages and lungs traps pathogens. Cilia on the epithelial cells lining the lungs move in a wave-like motion, moving mucus/pathogens out of the lungs and towards the throat

Blood clots: if skin is broken and starts to bleed, the blood will clot, stopping pathogens from entering the body

Question 5

Cilia move mucus away from the lungs. Describe how this protects the body from pathogens.

Answer 5

It stops pathogens entering the lungs where they can cause disease. When the mucus gets to the throat it is swallowed and the pathogens are destroyed by the acid in the stomach.

Question 6

A burn damages the skin, and a bad burn can completely break through the skin. First aid advice for a person who has suffered a burn includes covering the burn with clean cling film or a plastic bag. Explain why.

Answer 6

This stops the pathogen infecting the skin.

The burn has damaged the outer layer of cells so pathogens can enter the body easily.

Question 7

Chemicals in cigarette smoke paralyse the cilia in the epithelium of the airways. Smokers are more likely than non-smokers to suffer from lung infections. Explain why.

Answer 7

When the cilia are paralysed, they cannot move the mucus containing pathogens back up to the throat. The mucus travels down into the lungs, carrying pathogens with them. The pathogens can then infect the lungs.

Question 8

Give one example of a physical barrier and one example of a chemical defence that prevents pathogens entering the body.

Answer 8

unbroken skin/mucus in breathing system/blood clots

lysozyme in mucus/salivia/tears or hydrochloric acid in stomach