categories are all comprised of prokaryotic microorganisms lacking a membranebound nucleus. The distinction
made between prokaryotes (Bacteria vs Archaea) is based mainly on the differences in cellular composition and
is briefly described below. The Eukarya (eukaryotic) classification remained unchanged and still consists of all
nuclear bound microorganisms.
(sometimes referred to as Eubacteria, meaning ‘true bacteria’) constitute a large cohort of prokaryotic
microorganisms. They can be considered the everyday bacteria and are common in human daily life. They
have a variety of shapes by which they can be further classified.
Bacteria display many distinct morphologies (shapes), the most common include:
(curved rod) or
Aside from the shape of the bacterial cell, one should also note the cellular organization—cells may appear as
isolated (individual) cells or appear in chains or even clusters. Certain bacteria may also demonstrate motility
(swimming movements) while others do not. Examples of Eubacteria are: streptococcus, which have the
appearance of round chains; E. coli, which have the appearance of rodshaped, and mycobacterium
tuberculosis, a unicellular bacterium.
, the other prokaryotic class of microorganisms, have similar characteristics and shapes as Bacteria
(Eubacteria) and yet remain genetically and compositionally distinct. Most notably, they are able to survive in
extremely harsh environmental conditions such as high salt levels, acid conditions, high temperatures and
oxygenpoor conditions. As such, archaeons may also be referred to as extremophiles, based on the ‘extreme’
or atypical environments in which they can be found.
is a diverse category and consists of a wide range of microorganism. Due to high diversity and
complexity, eukaryotes can be subdivided into multiple categories, a process which is still debated today.
However, the unifying characteristic of all eukaryotic cells is the presence of a membranebound nuclear region
within the cell. For the purposes of this course, eukaryotic microorganisms will be classified as either: Animalia,
Plantae, Fungi and Protista.
consists of multicellular eukaryotic organisms and as the name suggests, includes animals, as well as
humans (and their cells) in their classification. All microorganisms in this category are
they are incapable of producing their own energy and thereby must absorb (consume) nutrients from the
environment and have the general characteristic of
(the ability to move).
are also multicellular eukaryotes but unlike Animalia, can obtain most of their energy from sunlight via