Solution-Why is glucose never an ingredient of starch agar

LAB Book Used: Leboffe and Pierce (2016). Brief microbiology laboratory theory and application (3rd ed.) Englewood, CO: Morton Publishing. ISBN: 9781617314773

Exercise 2-1(Ubiquity of Organisms):

Answers to these questions should show an understanding of why things grew the way they did and should not just repeat the observations in the table.

1. Did temperature have any effect on the growth of the organisms? Explain how you came to this conclusion.

2. Were you surprised in any way by the amount of growth on any of your plates? Explain which plates surprised you and in what way. If you were not surprised, explain why not.

3. Why would I recommend that students do not sample the work benches as a source of inoculum from the room?

4. Why was the plate that was left open to air left open for so long?

5. Are the organisms that are present on your plates pathogens or something else? Explain your thinking.

6. What limitations are present in this experiment regarding the culturability of organisms in general?

Exercise 5-7: Citrate Test

Exercise 5-10: Starch Hydrolysis (Amylase Test)

1. What is the purpose of having an uninoculated tube as a control? Please consider the purpose experienced lab technician would need this control, not why you, the student, might want one.

2. What molecule is being degraded (potentially) in Ex. 5-10? In which category of the four possible macromolecules would you place this molecule?

3. Why is it necessary to be sure to lightly inoculate the citrate medium rather than put lots of organism on the slant?

4. What use (other than seeing if the result is positive or negative) can a microbiologist make of results of metabolic testing of bacteria?

Exercise 5-7

1. Citrate can be transported into the cell and used for energy metabolism. What enzyme is required for citrate transport? Why do cell that do not have this enzyme fail to grow on the medium?

2. What is the approximate pH of uninoculated citrate agar? Why does the loss of citrate affect the pH of the medium? What metabolic byproducts are made that also affect the pH of the medium?

3. Does the presence of ability to do the Krebs cycle in a cell indicate whether the cell will be able to use the citrate agar? Explain.

Exercise 5-10

4. Why is it better to let the starch plates incubate longer than the prescribed time and not less than the prescribed time? Explain in terms of enzymes and substrate (what happens in the plate during incubation). Explain how this relates to the aIDition of iodine only after incubation in the starch plate.

5. What enzyme is used to break down the starch in the starch agar? Is this an exoenzyme or an endoenzyme? Explain your thinking.

6. Why is glucose never an ingredient of starch agar?

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