* Cell walls lack peptidoglycan (present in bacteria) * Lipids in cell membranes have a different structure from those in all other organisms * Distinctive rRNA sequences
Archaean Categories
* Methanogens * Extremophiles * Nonextreme Archae
Methanogens
* Obtain their energy by using H2 (g) to reduce CO2 to CH4 (g) * Are anaerobes that are poisoned by the slightest traces of O2 * Live in swamps, marshes, and intestines of mammals releasing CH4 (g)
Extremophiles
* Able to grow under conditions that seem extreme to us * Thermophiles - live in extreme hot * Cold-adapted - live in extreme cold * Halophiles - live in very salty environments * pH-tolerant - live in highly acidic or highly basic environments * Pressure-tolerant - live in the depths of the ocean at a minimum of twice the depth humans can survive (300m)
Bacteria
* More numerous than any other organism * Play critical roles throughout the biospheres, such as extracting N2 from the air * Highly diverse and blurred evolutionary links between species * 12-15 major groups of bacteria * Only living organisms with peptidoglycan in their cell walls
Eukaryotes
* First eukaryotes were unicellular * Probably evolved through endosymbiosis * Compartmentalized * Multicellular * Sexual reproduction