BIL 150 Chapter Notes - Chapter 6: Scanning Electron Microscope, Electron Microscope, Optical Sectioning
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Brightfield (unstained) passes light directly through specimen. Brightfield (stained) various dyes enhance contrast but cells are fixed. Fluorescence tagging with fluorescent dyes or antibodies. Phase-contrast enhances contrast by amplifying variation in density. Differential-interference contrast like phase-contrast exaggerate differences in density. Resolution = inversely proportional to the wavelength of light (or electrons) Therefore, electron beams have much shorter wavelengths than visible light: the scanning electron microscope (sem) is use for detailed study of the topography of a specimen. Dna: all cells have ribosomes, tiny complexes that make proteins according to instruction from the genes, prokaryotic cells (without nucleus (bacteria), is smaller and has a greater surface area to volume ratio. Larger organisms do not have larger cells, just more cells. A high surface area to volume ratio is important in cells that exchange a lot of material with their surroundings. Golgi apparatus, lysosomes, various kinds of vesicles and vacuoles, and the plasma membrane.
