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• Prokaryotes are divided into two domains: bacteria and archaea.
• • Most prokaryotes are unicellular, although some species form colonies.
• • Prokaryotic cells three most common shapes are spheres (cocci), rods (bacilli), and spirals.
• • An important feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment.
• • Eukaryote cell walls are made of cellulose or chitin.
• • Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides.
• • Using the Gram stain, scientists classify many bacterial species into Gram- positive and Gram-negative groups based on cell wall composition.
• • Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic, and they are more likely to be antibiotic resistant.
• • A polysaccharide or protein layer called a capsule covers many prokaryotes.
• • Some prokaryotes have fimbriae (also called attachment pili), which allow them to stick to their substrate or other individuals in a colony
• Sex pili are longer than fimbriae and allow prokaryotes to exchange DNA by conjugation
• • Most motile bacteria propel themselves by flagella that are structurally and functionally different from eukaryotic flagella.
• • In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from certain stimuli.
• • Prokaryotic cells usually lack complex compartmentalization.
• • Some species of bacteria also have smaller rings of DNA called plasmids.
• Prokaryotes reproduce asexually quickly by binary fission and can clone / divide every 1–3 hours.
• Prokaryotes have considerable genetic variation. Three factors contribute to this genetic diversity: Rapid reproduction, Mutation, Genetic recombination
• Prokaryotic DNA from different individuals can be brought together by transformation, transduction, and conjugation.
• • A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation.
• • Transduction is the movement of genes between bacteria by bacteriophages (viruses that infect bacteria)
• • Conjugation is the process where genetic material is transferred between bacterial cells.
• • Sex pili allow cells to connect and pull together for DNA transfer.
• • Phototrophs obtain energy from light.
• • Chemotrophs obtain energy fromchemicals.
• • Autotrophs require CO2 as a carbonsource.
• • Heterotrophs require an organic nutrientto make organic compounds.
• • These factors can be combined to give the

  four major modes of nutrition: photoautotrophy, chemoautotrophy, photoheterotrophy, chemoheterotrophy.
• • In nitrogen fixation, some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3).
• • Archaea are prokaryotes and share certain traits with bacteria and other traits with eukaryotes.
• • Some archaea live in extreme environments and are called extremophiles.
• • Extreme halophiles live in highly saline, salty environments.
• • Extreme thermophiles thrive in very hot environments.
• • Archaea appear to be more closely related to Eukarya than to Bacteria.
• • Bacteria include the vast majority of prokaryotes of which most people are aware.
• • Cyanobacteria are photoautotrophs that generate O2
• • Plant chloroplasts likely evolved from cyanobacteria by endosymbiosis.
• • Protist is the informal name of the kingdom of mostly unicellular eukaryotes, but there are some colonial and multicellular species.
• • Protista is no longer valid as a kingdom.
• • Mixotrophs combine photosynthesisand heterotrophic nutrition
• • Euglenozoa is a diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites.