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OCR a level biology question help

Explain why not all the pathogenic organisms that enter the body via the gas-exchange system and the digestive system cause disease.
Original post by Kagga123
Explain why not all the pathogenic organisms that enter the body via the gas-exchange system and the digestive system cause disease.

You can probably talk about how pathogens are trapped in the mucus in the gas exchange system before they can cause disease and for the digestive system e.g bacteria are killed by HCl.
The upper respiratory tract has goblet cells, which secrete mucous. Mucous traps bacteria and dust/debris. The ciliated epithelial cells in the URT then waft the mucous upwards, towards the stomach.

Stomach contains hydrochloric acid, which has a pH of 1-2. Most bacteria cannot survive this pH - their proteins and enzymes denature.

(Bacteria like V. cholerae and Salmonella, etc, have flagella that allows them to swim through the stomach and get to the small intestine, where they cause infection. )

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