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Name _________________ Period ______ BACTERIA [bacteria] [pl. of bacterium], microscopic unicellular prokaryotic organisms characterized by the lack of a membrane-bound nucleus and membrane-bound organelles. Once considered a part of the plant kingdom, bacteria were eventually placed in a separate kingdom, Monera . Bacteria fall into one of two groups, Archaebacteria (ancient forms thought to have evolved separately from other bacteria) and Eubacteria. A recently proposed system classifies the Archaebacteria, or archaea, and the Eubacteria as major groupings (sometimes called domains) above the kingdom level. Bacteria are grouped in a number of different ways. Most bacteria are of one of three typical shapes—rod-shaped (bacillus), round (coccus, and spiral (spirillum). The cytoplasm and plasma membrane of most bacterial cells are surrounded by a cell wall; further classification of bacteria is based on cell wall characteristics. They can also be characterized by their patterns of growth, such as the chains formed by streptococci. Many bacteria, chiefly the bacillus and spirillum forms, can move, swimming about with the aid of flagella; other bacteria have rigid rodlike hairs called pili that serve as tethers. Bacteria are prokaryotes. That means that they do not have any organelles that we have previously learned. No nucleus, no mitochondria, no chloroplasts. They do have DNA but it is not contained in a typical nucleus that has a membrane (covering). Below are the three main types of bacteria so color and read about each. The rod shaped bacteria are known as bacillus or if more than one, bacilli. Some bacteria are found in chains and the prefix “strepto” is placed before the bacteria type. Some bacteria put in milk is of this type (lactobacillus) and so is the infamous E. coli. Round Bacteria (coccus or cocci) The round bacteria are known as coccus or cocci(pl). The arrangement of the bacteria contributes to its name. Ever had “strep” throat? That would be short for streptococcus bacteria growing near your tonsils. Typical Spirillum The third kind of bacteria are the spiral shaped or spirilla. A lot of these kinds of bacteria cause disease. Things that cause disease are called pathogens. One such spiral bacteria is H. pylori and it causes gastritis.