Q: A bacterium is inoculated into a broth and after 3 hours, there are $$7 \times 10^5$ cells. If the generation time is 30 minutes, how many cells were originally inoculated?

$$7 \times 10^5$ \div 2^6$ = 1.09375 \times 10^4$ cells

Q: A urine sample is serially diluted. 1 mL from a 1:100 dilution is plated and 150 colonies are counted. What is the CFU/mL in the original sample?

$$150 \times 100 = 15,000$$ CFU/mL

Question 1

Which of the following best describes the ultimate function of metabolism in a microbe?

Accepted Answer

To reproduce the organism

Question 2

A bacterium is placed in an environment with high salt concentration (20% NaCl). Which term best describes a microbe that can tolerate and grow in this environment?

Accepted Answer

Facultative halophile

Question 3

Which equation correctly describes the exponential growth of a bacterial population by binary fission?

Accepted Answer

$$N = N_0$ 	imes 2^n$$

Question 4

A sample contains 10 cells of Staphylococcus aureus. After 4 generations, how many cells will be present?

Accepted Answer

$$10 	imes 2^4$ = 160$$ cells

Question 5

Which of the following is NOT a physical requirement for microbial growth?

Accepted Answer

Carbon source

Question 6

A microbe that uses light as its energy source and CO$$_2 as $$its carbon source is classified as a:

Accepted Answer

Photoautotroph

Question 7

Which enzyme is responsible for neutralizing hydrogen peroxide in aerobic bacteria?

Accepted Answer

Catalase

Question 8

A bacterium is inoculated into a broth and after 3 hours, there are $$7 	imes 10^5$ cells. If the generation time is 30 minutes, how many cells were originally inoculated?

Accepted Answer

$$7 	imes 10^5$ \div 2^6$ = 1.09375 	imes 10^4$ cells

Question 9

Which type of medium would you use to distinguish between lactose-fermenting and non-lactose-fermenting bacteria?

Accepted Answer

Differential medium

Question 10

Which of the following best describes a neutrophile?

Accepted Answer

Grows best around neutral pH

Question 11

A urine sample is serially diluted. 1 mL from a 1:100 dilution is plated and 150 colonies are counted. What is the CFU/mL in the original sample?

Accepted Answer

$$150 	imes 100 = 15,000$$ CFU/mL

Question 12

Which of the following is a toxic form of oxygen that can damage microbial cells?

Accepted Answer

OH$$^{\cdot} ($$hydroxyl radical)

Question 13

Which method would be most appropriate for counting only living, culturable bacteria in a water sample?

Accepted Answer

Viable plate count

Question 14

A bacterium is classified as a chemoheterotroph. What does this mean?

Accepted Answer

It uses chemical compounds for energy and organic compounds for carbon

Question 15

Which growth phase is characterized by a balance between cell division and cell death?

Accepted Answer

Stationary phase

Question 16

A sample of sea water is filtered and 24 colonies are observed on the membrane filter after incubation. What is the CFU per 100 mL?

Accepted Answer

24 CFU/100 mL

Question 17

Which of the following statements about agar is TRUE?

Accepted Answer

Agar is used to solidify culture media

Question 18

Which of the following is a growth factor required by some microorganisms for cytochrome function in the electron transport system?

Accepted Answer

Heme

Question 19

A bacterium is placed in a hypotonic solution. What is the most likely outcome?

Accepted Answer

The cell will swell due to water influx

Question 20

Which of the following best explains why most cells die in the absence of water?

Accepted Answer

Water is required to dissolve enzymes and nutrients for metabolism

Microbial Metabolism, Nutrition, and Growth: Study Notes

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