AS Level BiologyChapter 1.1 - Pathogens

What are they?

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.

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.

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.

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

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.

How do pathogens cause disease?

• By damaging the host’s tissues – e.g. influenza

• By producing toxins – e.g. cholera