Classification in kingdoms has had a fairly long history of going backwards and forwards in terms of which kingdoms to include, and how many there are in total. For example, one of the latest classifications puts forward 7 kingdoms.
The five-kingdom system of Prokaryotae, Protoctista, Plantae, Fungi and Animalia is already half a century old, has been up for debate as well, and will probably continue to evolve as we learn more about new species and the relationships between different kinds of organism. So, without further ado, let’s learn the basic principles of these kingdoms and what kind of organisms they represent.
Prokaryotae (or Monera)
This kingdom was used to refer to single-celled prokaryotes such as bacteria and archaea, and it rose to prominence in the 1920s because the important distinction between eukaryotes and prokaryotes was just beginning to take hold.
Pictured Lactobacillus is a bacterium added to so-called “probiotic” foods. Archaea look similar to bacteria, so weren’t distinguished for a while, before molecular biology revealed that their genes and protein synthesis machinery are very different and more closely related to those of eukaryotes. Many famous archaea are what’s called extremophiles because they were found in extreme environments such as boiling…