Diversity of Living Organisms - Five Kingdom Classification

R.H. Whittaker (1969) proposed the Five Kingdom Classification based on: complexity of cell structure, body organization, mode of nutrition, life cycle, and phylogenetic relationships.

Kingdom Monera: Consists of unicellular prokaryotes (e.g., Bacteria, Cyanobacteria). They lack a defined nucleus and membrane-bound organelles like mitochondria or chloroplasts.

Kingdom Protista: Includes all unicellular eukaryotes. This group acts as a link between Monera and the multicellular kingdoms. They may be autotrophic or heterotrophic.

Kingdom Fungi: Primarily multicellular (except yeast), heterotrophic (saprophytic or parasitic) organisms. Their cell wall is uniquely composed of Chitin, a polymer of $N-acetylglucosamine$ ($C_8H_{13}O_5N$)$_n$.

Kingdom Plantae: Multicellular, eukaryotic autotrophs that contain chlorophyll and perform photosynthesis to synthesize organic food ($C_6H_{12}O_6$).

Kingdom Animalia: Multicellular, eukaryotic heterotrophs that lack cell walls. They exhibit a holozoic mode of nutrition (ingestion of food).

Phylogenetic Relationship: The classification reflects evolutionary history, progressing from prokaryotic ($Monera$) to simple eukaryotic ($Protista$) to complex multicellular eukaryotic organisms ($Fungi$, $Plantae$, $Animalia$).