Micro mod 2

• Microorganisms are too small to be seen with the unaided eye and must be observed with a microscope
• The word microscope comes from the Latin word "micro" (small) and the Greek word "skopos" (to look at)
• Modern microbiologists use microscopes that produce magnifications ranging from ten to thousands of times greater than van Leeuwenhoek's single lens microscope
• Helicobacter pylori is a spiral-shaped bacterium first seen in cadaver stomachs in 1886
• Some microbes are more readily visible than others due to their size or observable features
• Microorganisms must undergo staining procedures before their cell walls, capsules, and other structures lose their colorless natural state
• Microorganisms and their components are measured in micrometers and nanometers
• A micrometer (μm) is equal to 0.000001 m (10^-6 m) and a nanometer (nm) is equal to 0.000000001 m (10^-9 m)
• Light microscopy uses visible light to observe specimens
• A compound light microscope has a series of lenses and uses visible light for illumination
• Total magnification of a specimen is calculated by multiplying the objective lens magnification by the ocular lens magnification
• Resolution in microscopy refers to the ability of lenses to distinguish fine detail and structures
• The resolving power of a microscope is influenced by the wavelength of light used
• To achieve high magnification with good resolution, immersion oil is used with the objective lens
• Darkfield microscopy is used to examine live microorganisms that are invisible in ordinary light microscopes or cannot be stained
• Phase-contrast microscopy allows detailed examination of internal structures in living microorganisms without the need for fixing or staining
• Differential interference contrast (DIC) microscopy uses differences in refractive indexes and two beams of light to produce brightly colored, nearly three-dimensional images
• Fluorescence microscopy takes advantage of substances that absorb short wavelengths of light and emit light at longer wavelengths
• Confocal microscopy is used to reconstruct three-dimensional images by illuminating one plane of a specimen at a time
• Two-photon microscopy (TPM) uses long-wavelength light and requires two photons to excite the fluorochrome to emit light
• Scanning acoustic microscopy (SAM) interprets the action of a sound wave sent through a specimen to study living cells attached to surfaces
• Electron microscopy is used to examine objects smaller than about 0.2 μm, such as viruses or internal cell structures
• In electron microscopy, a beam of electr
• Electron microscopy is used to examine objects smaller than about 0.2 μm, such as viruses or the internal structures of cells
• In electron microscopy, a beam of electrons is used instead of light
• The resolving power of the electron microscope is far greater than that of other microscopes due to the shorter wavelengths of electrons
• Electron microscopes are used to examine structures too small to be resolved with light microscopes
• Images produced by electron microscopes are always black and white, but they may be colored artificially to accentuate certain details
• Electron microscopes use electromagnetic lenses to focus a beam of electrons onto a specimen
• There are two types of electron microscopes: transmission electron microscope (TEM) and scanning electron microscope (SEM)
• Transmission Electron Microscopy (TEM)
• In TEM, a beam of electrons passes through a specially prepared, ultrathin section of the specimen
• The beam is focused on a small area of the specimen by an electromagnetic condenser lens
• Scanning Electron Microscopy (SEM)
• SEM provides three-dimensional views of specimens
• In SEM, an electron gun produces a finely focused beam of electrons called the primary electron beam
• The primary electron beam knocks electrons out of the surface of the specimen, and the secondary electrons produced are used to produce an image called a scanning electron micrograph
• Scanned-Probe Microscopy
• Scanned-probe microscopes use probes to examine the surface of a specimen using electric current
• Scanned-probe microscopes can be used to map atomic and molecular shapes, characterize magnetic and chemical properties, and determine temperature variations inside cells