Microorganisms are those organisms which can only be seen by a microscope. The most common known organisms are Fungi, Bacteria and Virus. These species have a specific importance for existence. Because :
- Microorganisms break down dead organic matter called decomposition.
- Microorganisms are further involved in ecological cycles such as the nitrogen and carbon dioxide cycle.
- Microorganisms cause diseases. This point may seem bad but it is good as our immunity system gets stronger by this.
Fungi were considered evolved plants long time ago but they have been divided into their own category. How fungi are different than plants and animals is:
- Fungi have cell wall but it is made of chitin not cellulose.
- It does not have chlorophyll
- It gains energy by secreting enzymes on organic matter and digests it.
- they store carbohydrates in the form of glycogen (animals store glucose in form of glycogen)
- These reproduce by spores.
The best example of a fungi is the mushroom or a mold. The mushroom is actually the fruiting body of the fungi. It produces spores which travel to new habitat and regrow into mushroom. The part of the mushroom in the soil has thread like structures called hyphea rather than roots. The hyphea digests organic matter. The whole network of the hyphea is considered as the mycelium of the fungi.
In a bread exposed to air a spore sets and grows inside the bread. The mycellium grows inside the bread and secretes enzymes breaking it down for gaining energy. This forms the mold.
Bacteria are smaller than any fungi or human cell. These reproduce asexually. There are many types of bacteria. Some may be rod shaped or spiral shaped or even sphere. These are smaller than any animal or plant cell.
Its structure is as follows:
- They have cell wall made of peptidoglycan unlike fungi or plant.
- They have cell surface membrane under the cell wall and have a simple cytoplasm. The cytoplasm have organelles like the plasmids which have the hereditary material. The other organelle found is a single chromosome strand.
- The outer layer of the cell wall has a capsule or slime layer which lubricates the cell and provides protection.
- Some may have a flagella (tail)
Bacteria can grow anywhere where there is organic matter to be found. It does have spores but these are not used to reproduce rather they are used in bad living conditions. The bacteria reproduce by cell division.
Viruses are not considered living organisms rather they are kept at the border of the living and the non living. The only characteristic virus shares with the living organisms is that it reproduces itself. Viruses particles are smaller than bacteria and are only seen by an electron microscope. They are not called cells as they do not have a nucleus. Viruses only survive on hosts which is why they are all called parasites.
The structure of the virus is as follows:
- Each have a genetic strand inside it either being DNA or RNA.
- The DNA or RNA are covered with a protein layer.
- The viruses do not have a membrane. Once they reproduce the host cell is destroyed causing its membrane to be torn as well. The viruses wrap the torn membrane around itself making the envelop.