Question

* If a population of 100,000 microbes was treated with an bactericidal chemical solution for two minutes and 90% of the population dies per minute, how many microbes remain after two minutes?

a. 100,000

b. 10,000

c. 1000

d. 100
*We wished to determine the abundance of bacteria in a sample of milk. To do this ten-fold serial dilutions of a one milliliter milk sample were prepared. One milliliter of the fourth 10-fold serial dilution was plated in a pour plate. After incubation, the plate had 35 colonies. How many bacteria were in the original milk sample?

a. 35 cells per ml

b. 350 cells per ml

c. 3,500 cells per ml

d. 35,000 cells per ml

e. 350,000 cells per ml

*According to our present understanding, each of the three major domains of organisms has what is known as its own universal ancestor.

a. True

b. False

*Both environmental conditions and nutrient resources strongly influence the composition of a microbial community.

a. True

b. False

Answer 1

*If a population of 100,000 microbes was treated with an bactericidal chemical solution for two minutes and 90% of the population dies per minute, how many microbes remain after two minutes?
c. 1000 During first minute, microbe count gets reduced to 10% of 100,000 which is 10,000. During the next minute, microbe count gets reduced to 10% of previous value of 10,000 which is 1,000.

*We wished to determine the abundance of bacteria in a sample of milk. To do this ten-fold serial dilutions of a one milliliter milk sample were prepared. One milliliter of the fourth 10-fold serial dilution was plated in a pour plate. After incubation, the plate had 35 colonies. How many bacteria were in the original milk sample?
e. 350,000 cells per ml. 4 serial dilution lead to a dilution factor of 10⁴. Hence we multiple the final colony count with the dilution factor.

*According to our present understanding, each of the three major domains of organisms has what is known as its own universal ancestor.
a. True

*Both environmental conditions and nutrient resources strongly influence the composition of a microbial community.
a. True