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Biology II1996The Effects of Antibiotics on Bacterial Growth Bacteria are the most common and ancient microorganisms on earth Mostbacteria are microscopic measuring 1 micron in length However colonies of bacteriagrown in a laboratory petri dish can be seen with the unaided eye There are many divisions and classifications of bacteria that assist inidentifying them The first two types of bacteria are archaebacteria and eubacteria Bothgroups have common ancestors dating to more than 3 billion years ago Archaebacteria livein environments where because of the high temperature no other life can grow Theseenvironments include hot springs and areas of volcanic activity They contain lipids butlack certain chemicals in their cell wall Eubacteria are all other bacteria Most of themare phototrophic ie they use the suns energy as food through the process ofphotosynthesis Another classification of bacteria is according to their need of oxygento live Those who do require oxygen to live are considered aerobes The bacteria whodont use oxygen to live are known as anaerobes The shape of specific bacteria provides for the next step in theidentification process Spherical bacteria are called cocci the bacteria that have arodlike shape are known as bacilli corkscrew shaped bacteria are spirilla andfilamentous is the term for bacteria with a threadlike appearance Hans Christian Joachim Gram a Danish microbiologist developed amethod for distinguishing bacteria by their different reaction to a stain The process ofapplying Grams stain is as follows the bacteria are stained with a violet dye andtreated with Grams solution 1 part iodine 2 parts potassium iodide and 300 partswater Ethyl alcohol is then applied to the medium the bacteria will either preserve theblue color of the original dye or they will obtain a red hue The blue colored bacteriaare gram-positive the red bacteria are identified as gram-negative Bacteria contain DNA deoxyribonucleic acid just like all cellsHowever in bacteria the DNA is arranged in a circular fashion rather than in strandsBacteria also contain ribosomes which like in eukaryotic cells provide
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