• Prokaryotes are single-celled organisms that do not have a membrane surrounding their DNA. Prokaryotes occupy two domains of life: Archaea and Bacteria.
• Members of the domain Archaea contain certain genes more similar to eukarya, which include plants, animals, and fungi, than to the genes of bacteria.
• The domain Archaea includes methanogens, which produce methane gas and live in anaerobic environments; extreme halophiles, which live in very salty environments;
Vocabulary prokaryote (p. 461) peptidoglycan (p. 462) methanogen (p. 462) halophile (p. 462)
thermoacidophile (p. 462) bacillus (p. 463) coccus (p. 463) spirillum (p. 463)
and thermoacidophiles, which live in extremely acidic, hot environments.
• Gram staining distinguishes between Gram-positive and Gram-negative bacteria. Bacteria also occur in several variations of three shapes: rods, spheres, and spirals.
• The domain Bacteria is classified into five groups: Proteobacteria, Gram-positive bacteria, Cyanobacteria, Spirochetes, and Chlamydia.
• Nitrogen-fixing bacteria fix nitrogen gas from the air into a form that both prokaryotes and plants can use.
streptococcus (p. 463) staphlyococcus (p. 463) Gram-negative bacterium
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