Microorganisms

What is a Microorganism?

In the previous section, we looked at living cells, the basic unit of life on Earth. We learned that some living things contain millions of cells and that others contain only 1 cell. In this section, we will focus on living things containing only 1 (or sometimes only a few) cells.

A Microorganism is a living thing that can only be observed using a microscope. Most microorganisms contain only 1 cell. There are millions of different types of microorganisms, many have a positive effect on our lives but some can have negative effects, such as cause diseases.

Types of Microorganisms

There a millions of different microorganisms on Earth, but all can be described in four main groups:-

  1. Bacteria.

  2. Viruses.

  3. Fungi.

  4. Protists.


Bacteria

The diagram below shows the three main shapes of Bacteria:-

The audio file below is a track from Jeff Wayne's War of the Worlds, based upon H.G. Wells classic novel.

As can be seen from the above audio clip, bacteria are microorganisms which can cause diseases. However, bacteria have many more functions, most of which have nothing to do with us at all!

The functions of bacteria include:-

  1. Helps plants to absorb Nitrogen from the soil.

  2. Break down cellulose in the stomach of certain animals to allow them to digest plant material.

  3. Causes dead organisms to decay, returning their nutrients to the environment.

  4. Used to create Insulin, a hormone needed by people with Diabetes.

  5. Digest waste products in sewage, as part of water purification.

  6. Some bacteria give off Oxygen as waste, this was the source of Oxygen in the atmosphere before plants existed.

There are thousands of other beneficial things that bacteria do, without which the Earth would look very different!

Diseases caused by bacteria include:-


Viruses

The diagram below shows the four main shapes of viruses:-

Viruses are much smaller than bacteria. Viruses are so strange that scientists are unsure if they qualify as being a living thing! Unlike most living things, viruses cannot reproduce on their own, they can only reproduce inside other cells.

To reproduce, the virus enters a cell, then they take control of the cell, forcing it to make thousands of copies of the virus. Eventually the cell then bursts open, releasing the new viruses which can go on to infect other cells.

Diseases caused by viruses include:-

The video below shows a detailed description of how viruses attack living cells.

Fungi

The diagram below shows the two main types of fungi:-

Fungi are neither plants nor animals, but a class of organisms all of their own. Most people can recognise the multicellular fungi (mushrooms and toadstools), but most do not realise that the moulds that grow on food are also fungi. Fungi specialise in decay, and are vital in the decomposition of dead material, especially wood.

Like bacteria, fungi have many more functions than causing diseases, most of which have nothing to do with us at all!

The function of fungi include:-

  1. Causes dead organisms to decay, returning their nutrients to the environment.

  2. The fungi Yeast is used in baking to make bread rise and in brewing to ferment sugar to make alcohol.

  3. Fungi can be used to make protein for meat substitutes (Quorn).

  4. Certain types of fungi can be eaten, but you should NEVER eat an unidentified mushroom, as some are highly poisonous.

  5. Fungi can kill other microorganisms such as bacteria, by creating chemicals called antibiotics.

There are thousands of other beneficial things that fungi do, without which the Earth would look very different!

Diseases caused by Fungi include:-


Protists

The diagram below shows the three main types of protists:-

Like fungi, protists are neither plants nor animals, but a class of organisms all of their own. They all are single-celled organisms, and display similarities with animals, plants and fungi, but are too different to be counted in those groups. The plant-like protist Algae is responsible for the creation of over half the Earth's Oxygen.

Diseases caused by protists include:-