Classification of Micro-organisms

An enormous, mostly invisible world

Life exists in a huge variety of forms living in different niches — from macroscopic plants and animals down to microscopic organisms. This lesson focuses on four groups of micro-organisms: bacteria, protista, fungi, and viruses, building on the classification basics from Grade 10.

Micro-organisms play a vital role in ecosystems

Far from being purely harmful, most micro-organisms help maintain balance in the environment and the wider web of life:

• Nitrogen-fixing bacteria live in symbiotic relationships in the root nodules of certain plants, converting atmospheric nitrogen into a usable form.
• E. coli bacteria live in the human intestine, assisting with digestion in a mutually beneficial relationship.
• Many bacteria and fungi act as decomposers, recycling nutrients back into ecosystems.

Micro-organisms that cause disease

Some micro-organisms are pathogens — they cause disease in plants, animals, and humans:

Immunity and disease control

Plants and animals have immune responses that help defend against infecting micro-organisms. Vaccinations work by preparing the immune system to recognise and fight a specific pathogen before a real infection occurs. Drugs, such as antibiotics, are also used to treat infections caused by bacteria.

Micro-organisms working for us

Humans have long put micro-organisms to work:

• Medicine production — e.g. insulin and antibiotics are produced using micro-organisms.
• Traditional food technology — e.g. yeast (a fungus) is used to produce beer, wine, and bread; bacteria are used to produce cheese.