Microorganisms – friend or foe?
We can’t see them. We can’t hear them or feel them, but they are with us. There are 10 trillion (10 x 1,000,000,000,000 or a million million) cells in the average body. For every cell, we have 10 times as many microorganisms – that’s 100 trillion microorganisms on and in our bodies! We are a walking, talking ecosystem.
But don’t worry – without microorganisms, we wouldn’t survive.
Hookworm
A hookworm is a parasite that can live in the human body.
Acknowledgement: CDC – National Center for Infectious Diseases
Microorganisms are small
A microorganism is a living organism that is so tiny it can only be seen with the aid of a microscope. Viruses are not microorganisms, as they are not classified as living. But they are interesting as they infect living organisms, including microorganisms.
Consider that the largest human cells are about the diameter of a human hair. Bacteria cells are one-hundredth the size of a human cell and viruses are much, much smaller again. If you imagine that a single virus was the size of an adult human, a bacterium (single cell) would be over 10 storeys high by comparison. A bacterium next to a human cell is like a tiny boat next to a big ship. Hundreds of thousands of bacteria could fit onto a pinhead.
Friend and foe
The main microorganisms in and on our bodies are protozoa, algae, fungi, bacteria. Most microorganisms are beneficial, for example, there are microorganisms in our large intestine that synthesise vitamins and allow them to be absorbed into the bloodstream. However, some are harmful, these are referred to as pathogens (disease-causing agents). These pathogens, often called germs or bugs, are a threat to all life forms. Viruses are also pathogens.
Let’s take a closer look at bacteria, parasites and viruses.
Bacteria
Bacteria are everywhere! A bacterium is a very simple form of life – just a single cell. They have different shapes – some look like balls, rods or spirals. They have a tough cell wall that protects them. They are like all living organisms and need to ‘eat’ (ingest) for energy and growth. They ingest starches and sugars that are found on all organic matter.
Bacteria reproduce through an asexual process called binary fission. Bacterial cells will make a copy of thier genetic material, then divide into two cells, these cells will grow, copy and divide over and over.
The good thing is that most bacteria are harmless, but pathogenic bacteria can make you sick.
Bacteria
A bacterium is just a single cell with a tough cell wall that protects it. The different shapes of bacteria enable us to place them in different family groups:
A. Bacilli with and without flagella
B. Streptococci
C. Staphylococci
D. Diplococci
E. Spirochete
F. Club rod
G. Filamentous
H. Streptobacilli
Parasites
A parasite lives on or inside its host organism in a very unequal relationship – it takes all its food from its host and doesn’t give anything back. Parasites can live on our bodies (like lice) or in our bodies and cause lots of different diseases. Parasitic worms (including hookworms – see Professor Le Gros’s research) can live in our bodies and make us sick. Some parasites are microorganisms like protozoa – a single-celled parasite. Diseases like malaria and giardia are protozoa.
Viruses
Viruses are are so basic (and tiny) that they are not even cells and are not classified as living. Viruses are just genetic material (DNA or RNA) wrapped up inside a strong ‘coat’ made of protein. There are many different types of viruses; they all require a host that enables them to multiply. A virus will hijack a cell in your body and change the instructions of the cell so that, instead of doing what it was designed to do, the cell begins to produce copies of the virus.
Virus replication
Watch this animated video of a virus infecting an animal cell through a process called endocytosis.
Some viruses will make so many new copies of the virus that the cell bursts open and releases all the virions, which then hijack many, many more cells. Other strains of viruses will exit a host cell in a process that creates a bud out of the host cell's membrane as they are released, leaving the host cell intact. Some viruses hibernate (become dormant) while they wait for the right conditions to come along.
Viruses have different shapes – rods, spheres or many-sided spheres. Pathogenic viruses can be very dangerous, but there are a few viruses that are not harmful. Researchers and scientists are trying to find ways of using these viruses to fight bacterial infections.
Related content
Find out more about virus strains, then explore some of the related science ideas and concepts on infections and the body’s first and second lines of defence.
Activity ideas
Help your students to investigate further with these great activity ideas that cover some of the big ideas in science:
Useful link
The smallest objects that we can see are about 0.1 mm long. You can see cells and bacteria with light microscopes, but to see anything smaller, such as a virus, you would need an electron microscope. See this interactive, from the University of Utah's Learn Genetics website, for a size comparison of microorganisms.
