2. What are pathogens?
• Pathogens are microorganisms that cause
diseases. There are four kinds of pathogens:
Bacteria, e.g. salmonella and cholera.
Viruses, e.g. influenza and AIDS.
Fungi, e.g. athlete’s foot and pneumocystis.
Protozoa, e.g. malaria and dysentery.
3. What is disease?
• Diseases are not one thing, but they are
compromised of certain symptoms. Some of
the symptoms of influenza are sneezing,
coughing, and a high temperature.
4. To be a pathogen, it must:
• Gain entry to the host.
• Colonise the host’s tissues.
• Resist the host’s defences.
• Damage the host’s tissues.
5. How do pathogens enter the body?
• The gas-exchange system – you can breathe in air
droplets that contain diseases such as influenza
and tuberculosis, which means you can be
diagnosed with these diseases.
• The digestive system – diseases like cholera are
water-borne diseases that affect the digestive
system (loss of water from the large intestines)
• Through cuts and broken skin – HIV/AIDS and
hepatitis
6. How does the body prevent pathogens
from entering the body?
• A mucous layer that covers the exchange
surfaces and forms a thick barrier so
pathogens can’t penetrate it.
• The production of enzymes to break down
the pathogens.
• The production of stomach acid to kill the
pathogens.
7. How do pathogens cause disease?
• By damaging the host’s tissues – e.g.
influenza
• By producing toxins – e.g. cholera
