Cracking the AP Biology Exam


Diversity of Organisms


Bacteria are prokaryotes, one-celled organisms, and they fall into two kingdoms: Archaebacteria and Eubacteria. Archaebacteria have several unique characteristics. Their cell wall lacks peptidoglycan found in eubacteria, and their plasma membranes contain unusual fatty acids. Another difference is that their ribosomes look more like those of eukaryotes. Some archaebacteria derive energy by converting CO2 and H2 to methane (methanogens) while others use H2S as their source of energy (chemoautotrophs). They include bacteria that live in hot springs (extremethermophiles) and those that only live in salty ponds (extreme halophiles).