Final answer:
In the five-kingdom classification system, all prokaryotes are grouped into a single kingdom, Monera, while in the six-kingdom system, they are split into two kingdoms: Bacteria and Archaea, reflecting their significant genetic and cellular differences.
Step-by-step explanation:
In comparing the five-kingdom system of classification with the six-kingdom system, all prokaryotes are grouped in one kingdom in the five-kingdom system, but are divided into two kingdoms in the six-kingdom version. Originally, the five-kingdom system introduced by Robert Whittaker in 1969 included the Kingdom Monera, which comprised all prokaryotic organisms, primarily unicellular and lacking nuclei and other organelles. However, with advancements in our understanding of the microbial world, particularly the pioneering work of Carl Woese, this single kingdom has been split into two separate kingdoms in the six-kingdom system: the Kingdom Bacteria and the Kingdom Archaea, to acknowledge the fundamental differences in the structure of cell membranes and ribosomal RNA sequences between these two groups.
So, while Linnaeus's original taxonomy organized life into kingdoms, classes, orders, families, genera, and species, with kingdoms being the largest and most inclusive category and species being the most specific, the current six-kingdom system provides a more accurate reflection of phylogenetic relationships among organisms. This more modern six-kingdom system aligns with the three-domain system comprising Bacteria, Archaea, and Eukarya, highlighting an evolutionary perspective that includes both genetic and morphological criteria for classification. The Eukarya domain includes kingdoms such as Animalia, Plantae, Fungi, and Protista.