1. Microorganisms around us

2. They are found in all living things such as plants and animals.
Definition
Microorganisms are very tiny one - celled organisms , viruses , fungi and bacteria and are found everywhere in the world.
They are found in all living things such as plants and animals.

3. Definition
There are more microorganisms on and inside our body than there are cells that make up our body.
Microorganisms can live in air , on land and in fresh or salt water environments.
Some of them pathogens can be harmful and causes disease but there are some microorganisms that are needed for living things to survive.  

4. Microorganisms
Fungi
Bacteria
Viruses
Protists

5. Bacteria
Singular bacterium:  Microscopic single-cell (unicellular) life form that exists practically everywhere in the Earth's environment, and is simpler than the cells of animals, fungi, and plants. Of about three million species of bacteria believed to exist, only about 4,000 are known.
Oligate aerobic bacteria, are those bacterial strains that require oxygen for their survival, growth and reproduction. In short, they need oxygen for cellular respiration (e.g. Bacillus, Pseudomonas aeruginosa, Mycobacterium tuberculosis).

6. Bacteria
Contrary to this, there are anaerobic bacteria, which live in a non-oxygenated environment throughout their life, e.g. Sulfate-reducing bacteria (SRB).
Intermediary to these two groups are facultative bacteria (e.g. E. coli, Staphylococcus)

7. Fungi
Fungi are microbes similar to plants, which do not possess any chlorophyll.
Fungi can grow either as single cells (yeasts) or as filamentous structures (moulds).
The hyphae of filamentous fungi (moulds) form compact tufts, collectively called a mycelium.

8. Viruses
Viruses depend on the host cells that they infect to reproduce.
When found outside of host cells, viruses exist as a protein coat or capsid, sometimes enclosed within a membrane.
The capsid encloses either DNA or RNA which codes for the virus elements.
While in this form outside the cell, the virus is metabolically inert
When it comes into contact with a host cell, a virus can insert its genetic material into its host, literally taking over the host's functions.
An infected cell produces more viral protein and genetic material instead of its usual products.
Some viruses may remain dormant inside host cells for long periods, causing no obvious change in their host cells (a stage known as the lysogenic phase).
When a dormant virus is stimulated, it enters the lytic phase: new viruses are formed, self-assemble, and burst out of the host cell, killing the cell and going on to infect other cells.