Download Microbiology: Observing Prokaryotic Cells - Size, Shapes, and Microscopy - Prof. K. Sulliv and more Study notes Biology in PDF only on Docsity! 2-1 Chapter 2: Observing the Microbial Cell SIZE OF PROKARYOTES Prokaryotes are generally smaller than 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- chains of more than 2 cells o Staphylococcus- grapelike cluster 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 Vibrio – curved rods 2-2 Microscopy Simple microscopes o one lens o magnify 50 – 300 X 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 sources and specimen o Focuses light rays up through specimen o No magnification Objective lens system o Closest to specimen o Typical scope has 10, 40, & 100X objective lenses o In each objective are multiple lenses Ocular lens system o Closest to your eye o Typically magnify 10x o Each ocular has multiple lenses Magnification A microscope with a 100X objective and 10X ocular has a total magnification of 1000X This means an object will appear 1000X larger than it is Can see bacteria at this magnification, but not internal structures Cannot see viruses Resolution ability to distinguish between 2 objects that are close together Limits the usefulness of a microscope Highest resolution of a typical light microscope is 0.2 micrometers This means that 2 objects closer than 0.2 µm to each other can’t be distinguished Resolution is determined by wavelength of light and numerical aperture Increasing resolution o Use shorter wavelength light o Wider lens closer to specimen Higher numerical aperture o Immersion Oil o Increase contrast (staining, etc.) o Multiple lenses Correct each other’s aberrations Wavelength of light o Shorter wavelength produces higher resolution o Blue light (400nm) is shortest wavelength so gives highest resolution Numerical aperture o Measure of light gathering ability of objective lens o Light bends as it passes through specimen into air; reduces resolving power o If space between specimen and objective (oil immersion objective only) is replaced with immersion oil, resolution increases Oil keeps light from scattering as much as in air
