barriers- lqc 3b

Question 1

skin

Answer 1

Contains the tough protein keratin, however the skin can be breached by wounds. Blood clotting helps prevent this. Skin flora outcompetes and prevents colonisation by other bacteria.

Question 2

mucosal membranes

Answer 2

Line the airways and gut. The mucus traps microbes and other particles. Beating cilia carry the mucus up to the throat to be swallowed. Secretions from eyes & nose contain the enzyme lysozyme that breaks down bacterial cell walls causing them to burst.

Question 3

stomach acid

Answer 3

Contains hydrochloric acid, giving a pH of less than 2.0. This kills most bacteria that enter with food or drink. This is also the optimum pH for the digestive enzyme pepsin.

Question 4

gut flora

Answer 4

‘Friendly’ bacteria found in both intestines. We have a mutualistic relationship with them. They aid digestion and outcompete pathogenic bacteria for food and space. The bacteria also secrete chemicals (lactic acid) to aid the defence against pathogens