Summary

This chapter traced how classification systems evolved from Linnaeus's simple two-kingdom scheme, through the recognition of bacteria, fungi and single-celled organisms that did not neatly fit as either 'plant' or 'animal', to R.H. Whittaker's five-kingdom system (1969) -- Monera, Protista, Fungi, Plantae and Animalia -- built on five criteria: cell structure, body organisation, mode of nutrition, mode of reproduction, and phylogenetic relationships.

Kingdom Monera contains all prokaryotes, divided into Archaebacteria (halophiles, thermoacidophiles, methanogens, adapted to extreme habitats) and Eubacteria (true bacteria, including photosynthetic cyanobacteria with nitrogen-fixing heterocysts, and the wall-less mycoplasma, the smallest known living cells). Kingdom Protista is a 'link' kingdom of unicellular eukaryotes, comprising chrysophytes (diatoms, golden algae), dinoflagellates (biflagellate, cellulose-plated, some causing red tides), euglenoids (mixotrophic, pellicle-bound), slime moulds (plasmodial, spore-forming) and protozoans (amoeboid, flagellated, ciliated and sporozoan forms). Kingdom Fungi consists of heterotrophic, chitin-walled organisms made of hyphae/mycelium, divided into Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes ('Fungi Imperfecti'), distinguished by mycelial structure and mode of spore formation. …