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Bacteria and Viruses. Bacteria. Prokaryotes are the oldest living things on Earth. Prokaryotes are single-celled organisms that do not have membrane-bound organelles. Prokaryotes are divided into two major groups: Domain Archaea Domain Bacteria. Archaea. Found in many places
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Bacteria • Prokaryotes are the oldest living things on Earth. • Prokaryotes are single-celled organisms that do not have membrane-bound organelles. • Prokaryotes are divided into two major groups: • Domain Archaea • Domain Bacteria
Archaea • Found in many places • Structurally very different from bacteria
Bacteria • Most known prokaryotes are members of this domain • One square inch of skin is host to over 100,000 bacteria!
Bacterial Structure • no membrane-bound organelles, but do have many internal structures • Have genetic material in the form of DNA • Often have small extra loops of DNA called plasmids. • Have ribosomes
Obtaining Energy and Nutrients • Bacteria differ in how they obtain energy and nutrients • Grouping prokaryotes based on their energy source separates them into photoautotrophs, chemoautotrophs, and heterotrophs.
Photoautotrophs • Get their energy from sunlight through photosynthesis • Includes purple sulfur and nonsulfer bacteria, green sulfur bacteria, and cyanobacteria. • Cyanobacteria are a major component of the plankton that floats in the ocean.
Chemoautotrophs • The only organisms that can get their energy from inorganic sources. • They use molecules that contain sulfur or nitrogen and simple organic molecules to obtain energy.
Heterotrophs • Most prokaryotes are heterotrophs and get both their energy and their nutrients from other organisms. • Most absorb their nutrients from dead organisms, but some are parasites or pathogens.
Reproduction and Adaptation • Prokaryotes reproduce by binary fission; exchange genetic material through conjugation, transformation, and transduction; and survive harsh conditions by forming endospores.
Binary Fission • Prokaryotes usually reproduce asexually by binary fission. • A single cell divides into two identical new cells. • Mutations do occur during prokaryotic reproduction, and new forms emerge frequently.
Genetic Recombination • There are 3 ways in which prokaryotes can form new genetic combinations. • Conjugation- two bacteria exchange genetic material. • Transformation- bacteria take up DNA fragments from their environment. • Transduction- genetic material is transferred by a virus.
Endospore formation • Endospore = thick-walled structures formed by bacteria to survive harsh conditions. • Can survive boiling, radiation, and acid. • Show no signs of life and can be revived after hundreds of years.