Stage 1 SACE Biology - Microorganisms

  • Organisms that are too small to be observed without a microscope.

  • They can be

  • Unicellular or multicellular

  • Plant or animal

  • Prokaryote or eukaryote

The 5 major groups are:

  1. Bacteria

  2. Archaea

  3. Fungi

  4. Protista

  5. Algae

Bacteria

  • Unicellular

  • Have no nucleus, only a cell wall and a membrane surrounding the cytoplasm

  • > Prokaryotes

  • Some have long tails, called flagella

  • They are classified according to their shape


  • Bacteria inhabit a wide range of environments from volcanic vents to 11km below sea. Many like the mild temperature of the human body.

  • Some are heterotrophic, others are autotrophic.

  • Those responsible for breaking down dead organic matter are of particular importance to the ecosystem and are called decomposers.

  • Bacteria can grow in very diverse conditions, which explains why they are found everywhere!

  • Although bacteria are excellent at adapting to their environments, certain conditions promote bacterial growth more than others.

Archaea

  • Inhabit some of the most extreme habitats on Earth, like hot springs or extremely acidic/alkaline waters.

  • They may be extremely abundant in environments that are hostile to all other life forms.

  • They are prokaryotic, and can use inorganic molecules like hydrogen sulphide (H2S) as a source of energy. 

Fungi

  • A fungus is a primitive (non-photosynthesising) vegetable.

  • They are eukaryotic, have cell walls and reproduce by releasing spores.

  • They feed on dead, decaying matter, breaking it down and helping return chemical elements to the natural environment. 

Fungi can decompose:

  • Paper

  • Clothing

  • Pesticides

  • Oil-based fuels

  • Paint

  • Water contamination

  • Glues and adhesives

  • Human bodies

  • Plastics

Penicillin

  • Discovered by Alexander Fleming in 1928

  • First antibiotic used by doctors

  • Works by bursting bacterial cell walls

  • Has saved 200 million lives

  • The effectiveness of penicillin is threatened by antibiotic resistance

Indigenous use of fungi

  • Indigenous people were particularly cautious around Omphalotus nidiformis ‘ghost fungus’ which glows in low light conditions. The fungus was avoided because bad spirits were associated with it, it was later proven to be toxic.

  • Podaxis pistillaris was used to darken the white hairs in the facial hair of old men for body painting, and there are also reports of it being used as a fly repellant. 

Protists

  • Simple, primitive animals that consist of just one cell (e.g. amoeba)

  • Most often found in water and soil.

  • There are 4 main groups, amoeba, flagellates, ciliates and spirozoa.

  • They are the largest and most diverse group of eukaryotic organisms on Earth (32,000 living species)

Algae

  • Simple plants (autotrophs) ranging from microscopic to seaweed to giant kelp (more than 30m long).

  • Include cyanobacteria such as blue-green algae, which are found all over the planet.

  • Provide the foundation of the aquatic food chains that support all fisheries and produce 50-85% of the air we breathe.