1) Main features of each microorganisms:
- 4 main types of microorganisms: Bacteria, Fungi, Viruses and Protozoa. They are specialized on infecting the body tissues where they reproduce and cause damage.
- Bacteria: most numerous types of organisms on the planet. Simple-celled organisms. Most bacteria are not harmful to humans. The bacteria that are infectious, are pathogens and cause diseases.
- Fungi: they are called microorganisms some are easily seen. Fungi play a vital role in decomposing dead material and recycling the nutrients to make them available for the growth of other plants. They tend to be ones that cause infections to the surface of the body. Their fibres grow in the upper layer of the skin which causes inflammation and damage. This can also provide a route into the body for other opportunistic infections
- Viruses: they are very tiny. All natural viruses cause disease including the common cold, influenza (flu), measles, mumps and rubella. They are not living cells themselves, and they can only reproduce inside other living cells. They can attack all different types of living organisms.
- Protozoa: they are large, single-celled organisms. Infection is usually spread by structures called cysts which are cells that have secreted a protective layer around them so that they can survive the journey from one host to the next. Once inside the new host, these cysts develop into the active protozoa which grow, reproduce and cause symptoms of disease in the new host. Not all protozoa are harmful to humans.
2) 
3) Body defences:
Barriers
- Mechanical: skin (It is the first barrieron of our body) and hair
- Chemical: mucus —> alimentary canal and respiratoria system. Saliva —-> alimentary canal. Hydrocloric acid —-> White Blood cells (phogocytosis and secretion of antibodies). Tears
