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Chapter 4
General microbiology - BIO 175
| Question | Answer |
|---|---|
| General principles of microscopy | 1) Resolution 2) Contrast 3) Wavelength 4) Magnification |
| Resolution | Ability to distinguish two points that are close together |
| The better the resolution... | The better two nearby objects are distinguishes from one another |
| Contrast | Differences in intensity between two objects or between an object and its background |
| Important to determine resolution? | Contrast |
| Staining and use of light that is in phase increases? | Contrast |
| Types of light microscopes | 1) Bright-field microscopes 2) Dark-field microscopes 3) Phase microscopes 4) Fluorescent microscope 5) Confocal microscope |
| Bright-field microscope | Object is dark against light background |
| Bright-field microscope - Simple | - Simple magnifying lens - Leeuwenhoek used simple microscope to observe microorganism |
| Bright-field microscope - Compound | - Series of lenses for magnification - Light passes through specimen into objective lens - Oil immersion lens creates resolution - Have one or two ocular lenses - Most have condenser lens (light through specimen) |
| Total magnification (compound microscope) | Objective lens x ocular lens |
| Dark-field microscope | - Best for observing pale objects (small or colorless cells) - Only lights rays scattered by specimen enter objective lens - Specimen appear light against dark background - Increases contrast and enables observation for more details |
| Phase microscope | - Examine living organism or specimen that would be damaged/altered by attaching them to slides or staining - Contrast is created because light waves are out of phase |
| Phase microscope types | 1) Phase-contrast microscope 2) Differential interference contrast microscope |
| Fluorescent microscope | - Direct UV light source at specimen - Specimen radiates energy back as a visible wavelength - Some cells are naturally fluorescent, others must be stained - Used in immunofluorescence to identify pathogens and to make visible proteins |
| UV light increases? | Resolution and contrast |
| Confocal microscope | - Use fluorescent dyes - Use UV lasers to illuminate fluorescent chemicals in a single plane - Resolution increased because light passes through pinhole aperture - Computer constructs 3D image from digitized images |
| Electron microscope | - Greater resolving power and magnification - Magnifies objects 10,000X-100,000 - Detailed view of bacteria, viruses, ultrastructure, and large atoms |
| Types of electron microscope | 1) Transmission electron microscopes 2) |
| Transmission electron microscopes | Provides details on internal structure |
| Probe microscope | Magnifies more than 100 million times |
| Two types of probe microscope | 1) Scanning tunneling microscopes 2) Atomic force microscopes |
| Purpose of staining | - Adds color to specimens - Increases contrast and resolution |
| Types of stains | 1) Simple 2) Differential (gram stain) 3) Special |
| Simple stains | - Composed of single basic dye - Used to determine size, shape, and arrangement of cells |
| Differential stains | - Use more than one dye - Used to distinguish between different cells, chemicals, or structures |
| Special stains | Simple stains used to identify specific microbial structures |
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