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Chapter_09_Solutions

Chapter_09_Solutions - Chapter 9 Visualizing Cells LOOKING...

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A213 DEFINITIONS 9–1 Green fluorescent protein (GFP) 9–2 Limit of resolution 9–3 Bright-field microscope 9–4 Image processing 9–5 Fluorescence microscope 9–6 Confocal microscope 9–7 Fluorescence resonance energy transfer (FRET) 9–8 Microelectrode TRUE/FALSE 9–9 False. Although objects smaller than the limit of resolution can be detected, their images will be blurred because of the unavoidable diffraction of light, which cannot be compensated for by computer-assisted image processing. 9–10 False. Although it is not possible to see DNA by light microscopy in the absence of a stain, chromosomes are clearly visible under phase-contrast or Nomarski differential-interference-contrast microscopy when they con- dense during mitosis. Condensed human chromosomes are more than 1 m m in width—well above the resolution limit of 0.2 m m. 9–11 True. Caged molecules are photosensitive precursors of biologically active substances such as Ca 2+ , cyclic AMP, and inositol trisphosphate. They are designed to carry an inactivating moiety attached by a photosensitive link- age. When exposed to intense light of the correct wavelength, the inactivat- ing group is split off and the active small molecule is released. Because laser beams can be tightly focused, caged molecules can be activated at defined locations in a cell. Thus, the time and location of activation are under the experimenter’s control. THOUGHT PROBLEMS 9–12 The components of the light microscope are labeled in Figure 9–16. Magnifica- tion of the specimen occurs at two points: in the objective and in the eyepiece. 9–13 All such imperfections scatter, refract, and reflect light, reducing the amount of light that goes through the specimen and adding spurious light rays that add a background haze to the image. As a result, both contrast and resolu- tion are reduced. LOOKING AT CELLS IN THE LIGHT MICROSCOPE eye eyepiece (ocular) objective specimen condenser light source retina Figure 9–16 Schematic diagram of a light microscope with components labeled ( Answer 9–12 ). In This Chapter LOOKING AT CELLS A213 IN THE LIGHT MICROSCOPE LOOKING AT CELLS A218 AND MOLECULES IN THE ELECTRON MICROSCOPE Chapter 9 9 Visualizing Cells
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9–14 The parallel light rays will converge (be focused) by passing through the lens, as shown in Figure 9–17A. The rays will also be focused by the inverted lens (Figure 9–17B). 9–15 In a dry lens a portion of the illuminating light is internally reflected at the interface between the coverslip and the air. By contrast, in an oil-immersion lens there is no interface because glass and immersion oil have the same refractive index; hence, no light is lost to internal reflection. In essence the oil-immersion lens increases the width of the cone of light that reaches the objective, which is a key limitation on resolution.
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