1-Kingdom System

  • Kingdom: Animalia
    • In the earliest system, all living things were grouped under “animals.”
    • This was very basic and didn’t account for differences between plants, fungi, bacteria, etc.

2-Kingdom System (Proposed by Linnaeus, 1735)

  • Kingdom Plantae
    • Included all organisms that were fixed in one place, like plants, algae, and fungi.
  • Kingdom Animalia
    • Included all moving organisms like animals.
    • Simple and easy but didn’t differentiate microscopic organisms or fungi.

3-Kingdom System (Proposed by Ernst Haeckel, 1866)

  • Kingdom Protista
    • A new group was created for single-celled organisms like algae and protozoa.
  • Kingdom Plantae
    • For plants, multicellular algae, and fungi.
  • Kingdom Animalia
    • For all multicellular animals.
    • This was an improvement, but still lumped fungi and some microbes incorrectly.

4-Kingdom System (Proposed by Herbert Copeland, 1956)

  • Kingdom Monera
    • Created for bacteria and other simple organisms without a nucleus (prokaryotes).
  • Kingdom Protista
    • Now contained all simple eukaryotic organisms (with a nucleus) like algae and protozoa.
  • Kingdom Plantae
    • Refined to include plants and multicellular algae.
  • Kingdom Animalia
    • For multicellular animals.

5-Kingdom System (Proposed by Robert Whittaker, 1969)

  • Kingdom Monera
    • Bacteria and archaea—tiny, single-celled organisms without a nucleus.
  • Kingdom Protista
    • Single-celled or simple multicellular organisms with a nucleus, like amoeba and algae.
  • Kingdom Fungi
    • Separate group for fungi (like mushrooms), which aren’t plants because they don’t photosynthesize.
  • Kingdom Plantae
    • All green plants that make food through photosynthesis.
  • Kingdom Animalia
    • All multicellular animals that eat other organisms for food.
    • This system was widely accepted for a long time.

6-Kingdom System (Proposed by Carl Woese, 1977)

  • Kingdom Archaebacteria (later renamed Archaea)
    • Simple, single-celled organisms that live in extreme environments (hot springs, salty water).
  • Kingdom Eubacteria (later called Bacteria)
    • Common bacteria found everywhere.
  • Kingdom Protista
    • Simple eukaryotes, including protozoa, slime molds, and algae.
  • Kingdom Fungi
    • Mushrooms, molds, and yeasts that absorb nutrients from their surroundings.
  • Kingdom Plantae
    • Plants that produce their own food via photosynthesis.
  • Kingdom Animalia
    • All animals that rely on consuming others for energy.

Key Differences in 6-Kingdom System:

  1. Archaea and Bacteria are separated because their cell structures and genetic material are very different.
  2. Protists remain a “miscellaneous” group for organisms that don’t fit elsewhere.

This classification is often used today, though scientists sometimes organize life into 3 Domains (Bacteria, Archaea, Eukarya) that encompass these kingdoms. This helps emphasize the major differences between prokaryotes and eukaryotes.