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ASSESSMENT Critical Thinking and Learning Outcomes Review 1. What are the two purposes of heat fixation? 2. What is the purpose of simple staining? 3. Why are basic dyes more successful in staining bacteria than acidic dyes? 4. Name three basic stains 5. Why is time an important factor in simple staining? 6. How would you define a properly prepared bacterial smear? 7. Why should you use an inoculating needle when making smears from solid media? An inoculating loop from liquid media?

Answer 1

1. Heat fixation allows-

a.  to kill organisms,

b. adhere them to the slides being used

2. The simple stain can be used to determine cell shape, size, and arrangement.

3. Basic dyes are positively charged and hence forms a strong ionic bond with negatively charged molecules like bacteria but acidic dyes are negatively-charged molecules that will repel the similarly charged bacteria hence they are less successful.

4. Three basic stains are - Crystal Violet. Carbolfuchsin. Methylene Blue.

5. Time is important because it creates a contrast between the bacteria and the stain. If you over or under stain you won't be able to see bacteria.

6. Properly prepared bacterial smear means the bacteria are evenly spread out on the slide, in such a concentration that they are adequately separated from each other and they are not distorted.

7. Solid media is denser over a smaller area so an inoculating needle is used to retrieve the specimen so not too much is transferred, while a liquid medium features a more spread out specimen so the inoculating loop can collect more liquid and enough specimen to observe.