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Kingdom Eubacteria and Kingdom Archaebacteria Characteristics of Bacteria Bacteria are by far the most abundant organisms on Earth. As a group they are very diverse, but they all share certain characteristics. 1. All bacteria are single-celled. 2. All bacteria are prokaryotes: Their DNA is not surrounded by a membrane. Cell organelles in bacteria are not surrounded by membranes. 3. The DNA of bacteria is made of a single chromosome. 4. All bacteria reproduce asexually by binary fission. Bacteria • As a group, bacteria are the smallest organisms. • They are usually 1–10 microns • A typical eukaryotic cell is about 10 times larger. Structure of a Bacteria • The structure is simple: • Cell wall: provides support and protection for the contents of the cell. • Cell membrane controls the passage of materials into and out of the cell. • The cytoplasm contains ribosomes, responsible for the formation of proteins • The DNA is a single chromosome formed into a ring • There is roughly 1/1000th the amount of DNA than in a typical eukaryotic cell. Projections Provide Locomotion • Some bacteria have whip-like flagella (singular: flagellum). • They act like propellers moving in reverse, drawing the organism forward. • Some bacteria have cilia (also called pili), tiny hair-like structures on the surface of the cell • They beat to move the bacteria forward Cell shape • spherical cell is called a coccus (pural: cocci) • a rod shaped cell is called a bacillus (plural: bacilli) • a spiral-shaped cell is called a spirillum (plural: spirilli). More names • monococci: cocci that live as separate cells • Diplococci: cocci that live in pairs. • Streptococci: cocci that live in linear chains • Staphlococci: cocci that live in grapelike clusters • Bacilli also exist as single cells, pairs (diplobacilli), or chains (streptobacilli). • Spiralbacteria exist only as single cells. Nutrition • There is a large variety of nutritional patterns among bacteria. Respiration • All living things must carry out cellular respiration to receive a supply of energy for life’s functions. • Bacteria differ in whether or not they require oxygen. Respiration • If cellular respiration involves oxygen to produce energy, bacteria are termed aerobes. • If oxygen is absolutely necessary for their survival, they are called obligate aerobes. • Those bacteria that can carry out cellular respiration in an oxygen-free environment are termed anaerobes. • If the presence of oxygen kills these organisms, they are called obligate anaerobes. • A third group of bacteria can survive with or without oxygen and they are called facultative anaerobes. Reproduction • All bacteria reproduce asexually and divide by the process of binary fission Reproduction • Bacteria can reproduce in 15 to 20 minutes as long as there is sufficient food, warmth, and space. • Under the right conditions, a single E.coli bacterium can produce between 10 and 100 million bacteria in 12 hours. Conjugation- sexual reproduction • During conjugation, two bacterial cells connect to each other by long protein bridges • The plasmid (ring of extra DNA) of one cell is transferred to the other cell. • When the process is completed, the bacterium that received the genetic material from the other cell now has a different genetic makeup • Having an altered genetic makeup increases the chance that a bacterium might possess a gene combination that enables the organism to adapt to worsening conditions. Bacteria and Disease • Only a small percentage of prokaryotes are pathogenic, or disease causing. • Pathogenic bacteria produce deadly substances (toxins) in the human body that cause disease symptoms. The Two Kingdoms of Bacteria • There are two kingdoms of bacteria: – Archaebacteria in the domain Archea – Eubacteria in the domain Bacteria Achaebacteria Archaebacteria • Most archaebacteria live in extreme environments. These are called extremophyles. • Other Archaebacteria species are not extremophiles and live in ordinary temperatures and salinities. Some even live in your guts! Archaebacteria • Some extremophile species love the heat! They like to live in boiling water, like the geysers of Yellowstone Park, and inside volcanoes. • These are called "thermophiles" which means "loving heat", and it would probably freeze to death at ordinary room temperature. • Other extremophile Archaea live in very salty, called hypersaline, environments. These salt-loving Archaea are called halophyles. • Other achaea are known as methanogens. • Methanogens are methane producers. Most of these bacteria use carbon dioxide as their carbon source. They are found in soil, swamps, and most animals digestive tracts Eubacteria • Eubacteria are more common and more widespread than acheabacteria. • There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water • There are approximately five nonillion (5×1030) bacteria on Earth, forming much of the world's biomass.
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