1 - Causes of Disease

My notes for chapter 1 (causes of disease) of Unit 1 (Biology and disease) for AS-level AQA Biology. These are my notes for what I specifically need to learn, so you may find them slightly incomplete from your point of view.

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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 (viruses inhibit synthesis of DNA, RNA and
proteins), resists the host's defences (break down cell membranes) and causes damage to host
tissue (through sheer number of pathogens). Some pathogens also produce toxins. To cause a
disease Pathogens must enter the body. Pathogens can enter the body through:
Respiratory system
o Breathe in air containing pathogens
o Mucus lining to trap pathogens/ ciliated cells
o Influenza, TB and bronchitis
Digestive system
o Eat/drink a food/drink containing pathogens
o Acidic conditions in stomach
o Cholera, typhoid and dystenry
o Enter through a break/cut
o Blood clotting
Urogenital system
2. Inherited diseases ­ caused by a faulty allele e.g. cystic fibrosis
3. Lifestyle/Environmental factors e.g. CHD/ Lung Cancer
1.2 Data and disease
Correlation between data does not conclude that one is the cause of the other, to conclude this we
would need to view some experimental evidence supporting this view.
1.3 Lifestyle and health
Lung disease
oCaused by Mycobacterium Tuberculosis which is transmitted by droplet infection, this
means it's a particular problem in places where people are close together e.g.
o The bacteria are engulfed by phagocytes in the lungs, but some are not killed as they
remain encased in hard nodules (tubercles).
o Bacteria remain dormant till host is immunosuppressed. When this happens they activate
and replicate.
o Bacteria destroy alveoli + produce scar tissue
Reduces surface area of alveoli (less O2 can diffuse into blood/ less CO2 out)
Increase diffusion distance (less O2 can diffuse into blood/ less CO2 out)
o Symptoms ­ severe coughing up of damaged tissues.
o Caused by smoke particles trapped in alveoli

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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 ­ diffusion gradient drops
o Symptoms ­ shortness of breath + wheezing
o Allergic reaction to pollen/dust
o Muscle around bronchioles contract + large volume of mucus is produced constriction of
o Air…read more

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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 blood pressure
Atheroma's = blood clot formation = less blood to heart = myocardial infarction…read more


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