REVIEW QUESTIONS 1. What advantage does staining a bacterial or yeast suspension
ID: 191855 • Letter: R
Question
REVIEW QUESTIONS 1. What advantage does staining a bacterial or yeast suspension have over observing cells in a wet mount? What disadvantages? Why do basic dyes such as methylene blue have a strong affinity for bacterial cells? What color would Gram positive bacteria appear if you omitted the iodine step of the Gram stain? If you omited the decolorization step? What color would Gram negative bacteria appear if you omitteo 2. 3. the iodine step? The decolorization step? . Make a table showing the Gram stain result (positive or negative) and cell shape (e.g. rod, coccus, vibrio) for each of the different species you used in this exercise. . Why is the color of the yeast cells not important?Explanation / Answer
1. wet mount:
advantages:
-they can be used to view living organisms
-motility can be observed.
-characteristic arrangement, grouping, of organisms is not interrupted because a heat-fix smear not required.
disadvantages: quickly dry out, limiting the opportunity for viewing
-oil immersion objective cannot be used
-microbes are difficult to see because of the same index of refraction as water.
staining:
advantages: microbes are much easier to see because of increased contrast in the background
- cover slip is not used so oil immersion objective can be used, increasing the potential for total magnification of 1,000X
- stained smears are permanent & can be used for further observations for a longg time.
disadvantages: microbes are heat-fixed to the slide, which causes them to die and it become.impossible to view mobility
- natural arrangement of bacteria get disrupted in preparation of the smear
2. basic dyes are cationic, positive charged and have strong affinity for the negative constituents of the bacterial cells.
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