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chapter+2+outline+fall08 - Chapter 2 Observing the...

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Chapter 2: Observing the Microbial Cell SIZE OF PROKARYOTES Prokaryotes are generally smaller then eukaryotes Small size allows nutrients to reach all parts of cell quickly Prokaryotic cells can be as small as 0.2μm. The smallest eukaryotic cells are 2μm. Cocci- typically has diameter of 2 µm Some microbiologists have proposed that bacteria smaller than 0.2 μm exist in nature, cells referred to as nanobacteria If one considers the space needed to house all essential molecules of life, it is unlikely they could exist within a volume available in a cell less than 0.1 μm. Prokaryotic cells can have a wide variety of cellular morphologies , which are often helpful in identification. Bacterial Shapes 1. Simplest shape is sphere o singular- coccus o plural- cocci Arrangement: o Coccus- single cells o Diplococcus- 2 cells o Streptococcus- chaings of more than 2 cells o Staphylococcus- grapelike clusters of cells o Tetrads- packets of 4 cells 2. Most common shape is rods o Singular- bacillus o Plural- bacilli Can be very long & thin or short & fat Occur singly or in chains 3. Spirals: Rigid spiral-shaped bacteria are called spirilla (singular- spirillum) Flexible spiral-shaped bacteria are called spirochetes (flexible corkscrew shaped cells with multiple curves) Vibrio – curved rods Microscopy Simple microscopes o one lens o magnify 50X – 300X
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Compound microscopes o multiple lenses o Much higher magnification Ones in 2051 lab magnify 1000X Lens System of Compound Microscopes Condenser lens o located between light source and specimen o Focuses light rays up through specimen
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