1. A plate with a final dilution factor of 107 produced 210 colonies. a) What was the original concentration in the sample? b) If you were to dilute the original sample with a dilution factor of 108, how many colonies would you count on the plate? c) If you were to dilute the original sample with a dilution factor of 106, how many colonies would you count on the plate?
1. A plate with a final dilution factor of 107 produced 210 colonies.
a) What was the original concentration in the sample?
b) If you were to dilute the original sample with a dilution factor of 108, how many colonies would you count on the plate?
c) If you were to dilute the original sample with a dilution factor of 106, how many colonies would you count on the plate?
2. Sally Monella found 344 bacterial colonies on one of her plates. She had prepared this plate after a serial dilution of a culture of Yersinia pestis. She had pipetted 1 ml sample of diluted Yersinia pestis from a tube with the overall dilution factor of 106 into a plate and covered it with agar. She used this plate to calculate the concentration in cells/ml of a bacterial culture.
a) How many organisms were in the original culture?
b) Were her results valid? Why or why not?
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