Disease And Immunity: Disease
12.1 Disease
Key Definitions
- Pathogen: Disease-causing organism (bacteria, viruses, fungi, protoctists).
- Transmissible disease: A disease in which the pathogen can be passed from one host to another.
Transmission Of Pathogens
- Direct contact: Blood, body fluids (HIV, hepatitis).
- Indirect contact: Contaminated surfaces, food, animals, air.
Barriers To Infection
- Skin (physical barrier).
- Nose hairs + mucus (trap particles).
- Stomach acid (kills pathogens).
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Vectors
- Organisms that transmit disease without causing it.
- Example: Mosquito (transmits malaria).
Examples Of Diseases
- Malaria:
- Caused by parasite (Plasmodium).
- Transmitted by female Anopheles mosquito.
- Controlled by insecticides, mosquito nets, draining stagnant water.
- HIV/AIDS:
- Virus attacks lymphocytes → weakens immune system.
- Spread via unprotected sex, sharing needles, infected blood, mother to child.
- Controlled by education, safe practices, antiviral drugs.
- Cholera:
- Bacterium in contaminated water.
- Produces toxin → secretion of chloride ions → water follows → diarrhoea and dehydration.
- Controlled by clean water, sanitation, food hygiene.
Written And Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions And 11 World Records For Educate A Change O Level And IGCSE Biology Full Scale Course
Lifestyle Diseases
- Excessive alcohol: Reduced self-control, slower reaction times, liver damage, social problems.
- Tobacco smoke: Contains nicotine, tar, carbon monoxide.
- Bronchitis, emphysema, lung cancer, heart disease.
- Smoking in pregnancy → low birth weight in babies.