chapters 3 - 6 - Chapter 3 Contrast necessary to see...

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Chapter 3 Contrast : necessary to see organelles and the object more clearly o If not, the object just blends in with the medium Intensity Contrast : Brightness of the 2 components appearing different in the image Color Contrast: Wavelength of light striking the object and the background are different, giving the background a different color TYPES OF MICROSCOPES o Brightfield Microscopes: Bright Background: field of view Achieve contrast when components in object absorb, refract, or reflect some of the light o Darkfield Microscopes : Direct light from the condenser through the object at a great angle Most light is reflected and leaves the medium and the object Little light passes through the microscope Dark background and illuminated object Shows the components of the object that has the highest refractive index (bright components against Dark Background) Negative image produced o Phase Contrast Differences in refractive indices produce the contrast Illuminating light directed from the condenser toward the object while traveling only in certain well-defined directions Light that interacts with the object is refracted/diffracted leaves the specimen at different angles Difference appears in the brightness of the image and the background o Differential Interference Contrast (DIC) microscopes complex Beam of light is split in 2; each beam is polarized separately by passing through the object Beam 1: passing through the portion of interest Beam 2: passing parallel to the portion as a reference beam o Nomarski Differential Interference Contrast (NDIC) Specimen Preparation for Light Microscopy o Darkfield, Phase Contrast, and NDIC microscopy are useful for improving contrast Cells can remain alive and perform normal functions o Stain: kills cells, binds to organelles Stains to specific organelles: ex: chromatin staining o Vital stains: bind to components of living cells without killing them o Wet mount: preparation of a slide with liquid (aq) and coverslip Inconvenient for photography
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CHAPTER 4 Axenic culture : Culture of only 1 species of organism o Single-celled o Harder to do with multicellular organisms Pros for Axenic Culture o Can study more clearly the direct effects of a single species o Ecological relationships = the effects of other species on the axenic culture o Can culture the axenic culture more – with the same set of conditions Exponential Growth : GROWTH KINETICS o Sigmoidal (S-shaped): Log phase Exponential phase Stationary Phase Declining phase o lnA = lnA 0 + kt linearized curve made into a straight line o Graph as ln(cell density) vs. time o Doubling time = ln2/k o Linear regression analysis = “best fit” line Sampling Method Hemacyanometer: Tool of measuring cell density under the microscope Spectrophotometer: measures cell density o Directs a beam of light through a prism of desired wavelength
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This note was uploaded on 03/20/2008 for the course BIO 205L taught by Professor Hanson during the Fall '07 term at University of Texas.

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chapters 3 - 6 - Chapter 3 Contrast necessary to see...

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