Biological Classification (Introduction)

BIOLOGICAL CLASSIFICATION

• Ear­ly Clas­si­fi­ca­tion:
  • Dri­ven by prac­ti­cal needs (food, shel­ter, cloth­ing).
  • Aris­totle’s sim­ple clas­si­fi­ca­tion:
    • Plants: Trees, shrubs, herbs (based on mor­phol­o­gy).
    • Ani­mals: Red-blood­ed vs. non-red-blood­ed.
• Lin­naeus’ Two-King­dom Sys­tem:
  • Plan­tae & Ani­malia
  • Lim­i­ta­tions:
    • Did­n’t dif­fer­en­ti­ate between prokary­otes and eukary­otes.
    • Did­n’t sep­a­rate uni­cel­lu­lar and mul­ti­cel­lu­lar organ­isms.
    • Grouped pho­to­syn­thet­ic (algae) and non-pho­to­syn­thet­ic (fun­gi) organ­isms togeth­er.
• Need for a New Sys­tem:
  • Many organ­isms did­n’t fit into plant or ani­mal cat­e­gories.
  • Need to incor­po­rate char­ac­ter­is­tics beyond mor­phol­o­gy:
    • Cell struc­ture
    • Cell wall com­po­si­tion
    • Mode of nutri­tion
    • Habi­tat
    • Repro­duc­tion meth­ods
    • Evo­lu­tion­ary rela­tion­ships
• Mod­ern Clas­si­fi­ca­tion:
  • King­doms beyond Plan­tae and Ani­malia intro­duced.
  • Five-king­dom sys­tem (includes Mon­era, Pro­tista, Fun­gi)
  • Under­stand­ing of which organ­isms belong to spe­cif­ic king­doms has evolved.
  • Ongo­ing changes and refine­ments to clas­si­fi­ca­tion sys­tems.

Key King­doms:

• Mon­era: Prokary­ot­ic organ­isms (e.g., bac­te­ria)
• Pro­tista: Most­ly uni­cel­lu­lar eukary­ot­ic organ­isms (e.g., amoe­ba, algae)
• Fun­gi: Eukary­ot­ic, het­erotroph­ic organ­isms with chiti­nous cell walls (e.g., mush­rooms, yeasts)
• Plan­tae: Eukary­ot­ic, mul­ti­cel­lu­lar, pho­to­syn­thet­ic organ­isms with cel­lu­lose cell walls (e.g., trees, ferns)
• Ani­malia: Eukary­ot­ic, mul­ti­cel­lu­lar, het­erotroph­ic organ­isms with­out cell walls (e.g., insects, mam­mals)

Oth­er Impor­tant Groups:

• Virus­es: Non-cel­lu­lar enti­ties, con­sid­ered non-liv­ing by some.
• Viroids: Infec­tious agents com­posed of RNA.
• Lichens: Sym­bi­ot­ic asso­ci­a­tions between fun­gi and algae.