week 3 prelab fall 11

week 3 prelab fall 11 - - Exercises 3-10, 3-13, 3-7, and...

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Week 3 Prelab Questions M/T Sept. 12, 13 - Exercises 3-6, 3-5, 3-8 1. Explain how a cell remains unstained using the negative staining technique. How does this differ from simple staining? 2. When preparing a negative stain, what is NOT done before staining in this procedure that is found in the protocols of the other two staining techniques done in this class period? Why? 3. Looking at diagram 3-85, why is it important to spread the sample across the slide as shown in step 5? Should you look at the thinner or thicker area of sample on step 6? Why? 4. Why are methylene blue, crystal violet, and safranin referred to as basic stains? 5. Why do you not want to add too much water when preparing the bacterial smear? 6. Why should you not hold the slide in the flame too long when heat fixing? 7. How is acid fast staining used diagnostically? 8. What is the purpose of a counterstain? 9. What is the purpose of heating the slide while performing the acid fast stain? W/R Sept. 14, 15
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Unformatted text preview: - Exercises 3-10, 3-13, 3-7, and Supplement pg. 4 1. For best results, should a fresh culture be used when performing an endospore stain? Why or why not? 2. What is the purpose of covering the smear with bibulous paper when performing the endospore stain? 3. What are two possible problems that are encountered when performing a flagella stain? 4. How would a Gram positive cell appear immediately after decolorization? A gram negative cell? Why? 5. Why is the Gram stain more helpful than a simple stain when identifying an unknown organism? 6. Give two reasons why a Gram stain may not yield clear results. 7. What is the purpose of the mordant when Gram staining? Why does this not affect Gram-negative cells. 8. What is the purpose of the low agar percentage in the motility plates? How does this affect incubation? 9. What do you expect the motility results to be for the motile and non-motile strains of E. coli ?...
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