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KEY CONCEPT Bacteria and Archaea are both single-celled prokaryotes. Prokaryotes are widespread on Earth. • Prokaryotes can be grouped by their need for oxygen. – obligate anaerobes are poisoned by oxygen – obligate aerobes need oxygen – facultative aerobes can live with or without oxygen • Domain Bacteria includes prokaryotes in the kingdom Eubacteria. – one of largest groups on Earth – classified by 1) shape 2) need for oxygen 3) diseases caused Bacteria and archaea are structurally similar but have different molecular characteristics. • Bacteria commonly come in three forms. – rod-shaped, called bacilli – spiral, called spirilla or spirochetes – spherical, called cocci Lactobacilli: rod-shaped Spirochaeta: spiral Enterococci: spherical • Archaea have many shapes. • Bacteria and archaea have similar structures. – plasmid – flagellum pili plasma – pili membrance chromosome cell wall plasmid This diagram shows the typical structure of a prokaryote. Archaea and bacteria look very similar, although they have important molecular differences. flagellum • Bacteria have molecular differences. – The amount of peptidoglycan within the cell wall can differ between bacteria GRAM NEGATIVE GRAM POSITIVE – Archaea have different lipids entirely Domain Archaea includes prokaryotes in the kingdom Archaea. • cell walls chemically different from bacteria – do not contain muramic acid – membrane lipids contain branched carbon chains • differences discovered by studying RNA • known for living in extreme environments KEY CONCEPT http://www.funsci.com/fun3_en/protists/exhibition. htm#green Kingdom Protista is the most diverse of all the kingdoms. Protists can be animal-like, plantlike, or funguslike. • Protists are eukaryotes that are not animals, plants, or fungi. • Animal-like protists consume other organisms. – heterotrophs – single-celled • Plantlike protists are photosynthetic. – single-celled, colonial, or multicellular – no roots, stems, or leaves • Funguslike protists decompose dead organisms. – heterotrophs – can move, whereas fungi cannot Protists are difficult to classify. • Protist classification will likely change. – Some protists are not closely related. – Molecular evidence supports reclassification.