Microbiology

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 function 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 functions 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:-

Growing Microorganisms

Colonies of microbes can be grown rapidly on Agar (a jelly-like food source) in Petri dishes. The process of growing microbes is known as "culturing microbes".

Microbes require a source of food, water, oxygen and an appropriate temperature to grow.


Aseptic Techniques

In order to grow microbes safely, aseptic techniques must be used, so that only the microbes required will be grown.

Aseptic means "no infection", but in this context it means no contamination with unwanted microorganisms.

We can prevent contamination by:-

  1. Disinfecting the work space before starting.

  2. Washing our hands.

  3. Using a bunsen next to the kit creating an updraft to prevent microbes falling onto the petri dish from the air.


The step by step process below should be followed when culturing microbes:-

Biotechnology

Using microbes has many uses within industry, creating millions of jobs around the world, in a range of ways. Some of the uses of microbes are:-

  1. Biological breakdown of sewage - Bacteria used to break down waste as part of sewage treatment.

  2. Biological breakdown of oil spills - Bacteria used to break down oil reducing the impact of oil spills.

  3. Manufacturing of Insulin - Insulin, a vital treatment for Diabetes, is creating using transgenic bacteria.

  4. Bread making - The fungi Yeast is used to create Carbon Dioxide to make bread rise.

  5. Alcohol production - The fungi Yeast is used to break down sugars creating alcohol as a waste product.

  6. Nematode treatment - Specific species of protists can be applied to garden plants to kill pests or diseases.


The Wonder of Yeast

Yeast is the earliest example of Biotechnology. Yeast has been used as long as farming has existed, since prehistoric times. Yeast is naturally occurring and easy to use, allowing prehistoric farmers to create two very important products, Bread and Beer.

Yeast is a single-celled member of the fungi family and can be found naturally all over the world, in over 1500 different species. It is the Yeast's respiration process and waste products that make it so useful.

The following formula describes the respiration of Yeast:-

It is the two waste products, Carbon Dioxide and alcohol, that are useful to us.


Bread Making

Yeast is essential in making bread rise. When Yeast is added to a dough, the Yeast uses the sugars in the dough for respiration. By leaving the dough in a warm place for a short time (this is known as "proving" the dough) the Carbon Dioxide released by the Yeast causes the dough to double in size. It is this release of Carbon Dioxide that causes the bread to rise.

The diagram below shows the step by step process to make a loaf of bread:-

Alcohol Making

Yeast is essential in making alcoholic drinks. When Yeast is added to a sugary solution, the Yeast uses the sugars in the liquid for respiration, in a process known as Fermentation.

This respiration releases Ethanol as a waste product, making the liquid alcoholic.

The video below shows the step by step process of using Yeast to make Whisky:-

Fermentation

The fermentation process (using Yeast to convert sugar into alcohol) can be demonstrated in the school lab.

The method below shows how to convert the sugars in ribena into alcohol:-