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• Introduction
• Bacteria
• Fungi
• Protists
• Viruses

Archaebacteria

Live under extreme conditions, often requiring absence of oxygen. Some live at elevated temperatures, even above the boiling point of water, some live in saturated brine, some live deep in the earth or in hydrothermal vents in the seafloor. They may metabolize hydrogen sulfide, or produce methane in anoxic environments.

Eubacteria

The oldest, simplest, and most abundant microorganisms. Representatives are found eveywhere life is possible. Cyanobacteria (blue-green "algae") may be the oldest form of life still extant. They were initially responsible for free oxygen in the earth's atmospherer.

Protists

Single-celled eukaryotes of an enormous diversity are lumped together for convenience in this artificial assemblage.

Fungi

Fungi are heterotrophic. They secrete enzymes which break down organic molecules external to the fungal cells, then absorb the products. Fungi have stiff cell walls made of chitin. Most are terrestrial.

Plants

Multicellular organisms with cellulose cell walls. Most are photosynthetic.

Animals

Multicellular heterotrophic organisms. Generally motile in at least some stages of their life cycle (most are motile in all stages)

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