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AQA AS Biology Unit 1 Biology and Disease

1. Causes of Disease
1.1 Pathogens
Disease is caused by

1. PATHOGENS (infectious diseases) e.g. cholera and TB

A pathogen is a microorganism (e.g. bacteria, fungi and viruses) that causes disease. A pathogen
gains entry to the host, colonises the host's tissues…

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AQA AS Biology Unit 1 Biology and Disease

o Alveoli break down + walls thicken (reduces surface area + increases diffusion distance
(less O2 can diffuse into blood/ less CO2 out))
o Loss of elastic tissue (alveoli cannot recoil ­ more difficult to expel air from lungs)
Air not replenished…

Page 3

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AQA AS Biology Unit 1 Biology and Disease

Nicotine stimulates adrenaline production = increased heart rate = raised blood
Nicotine makes red blood cells more `sticky' = higher risk of thrombosis
o High blood pressure
Increases damage to artery walls = increased risk of atheroma formation =
increase in…


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