Q: A scientist wants to estimate the number of bacteria in a sample using serial dilution and viable plate counts. If 0.1 mL of a $$10^{-4}$$ dilution yields 50 colonies, what is the original concentration of bacteria per mL? Use the formula $$\text{CFU/mL} = \frac{\text{Number of colonies}}{\text{Volume plated (mL)} \times \text{Dilution factor}}.$$

$$\text{CFU/mL} = \frac{50}{0.1 \times 10$$^{-4}$$} = 5 \times 10^6$

Question 1

Which of the following best describes a chemoheterotroph?

Accepted Answer

An organism that uses organic compounds as both an energy and carbon source.

Question 2

A bacterium is found growing only at the bottom of a thioglycolate broth tube. What is the most likely classification of this organism?

Accepted Answer

Obligate anaerobe

Question 3

Which of the following growth factors is required by mycoplasmas for cell membrane synthesis?

Accepted Answer

Cholesterol

Question 4

A microorganism isolated from a hot spring that grows optimally at 70°C would be classified as a:

Accepted Answer

Thermophile

Question 5

Which of the following is NOT a benefit to microbes living in a biofilm?

Accepted Answer

More choices for reproductive mates, thus more genetic diversity

Question 6

Which of the following best explains why obligate anaerobes are killed by oxygen?

Accepted Answer

They lack enzymes to detoxify reactive oxygen species.

Question 7

A bacterium that grows best at a pH of 9 would be classified as a(n):

Accepted Answer

Alkalinophile

Question 8

Which of the following statements about binary fission is correct?

Accepted Answer

It results in exponential (logarithmic) population growth.

Question 9

If a bacterial culture starts with 5 cells and has a generation time of 20 minutes, how many cells will there be after 1 hour? Use the formula $$N = N_0$ 	imes 2^n$$, where $$n is $$the number of generations.

Accepted Answer

$$N = 5 	imes 2^4$ = 80$$

Question 10

Which type of culture medium would you use to distinguish between bacteria that ferment lactose and those that do not?

Accepted Answer

Differential medium

Question 11

A scientist wants to isolate a pure culture from a mixed sample. Which technique should they use?

Accepted Answer

Streak-plate method

Question 12

Which of the following best describes the stationary phase of a bacterial growth curve?

Accepted Answer

The rate of cell division equals the rate of cell death.

Question 13

Which of the following methods would be most appropriate for counting the number of viable bacteria in a water sample?

Accepted Answer

Membrane filtration

Question 14

A bacterium that can grow in the presence or absence of oxygen but does not use oxygen for metabolism is classified as a(n):

Accepted Answer

Aerotolerant anaerobe

Question 15

Which of the following is a real-world example of a biofilm?

Accepted Answer

Dental plaque on teeth

Question 16

Which of the following best explains why nitrogen fixation is essential for life on Earth?

Accepted Answer

It converts nitrogen gas into forms usable by most organisms.

Question 17

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

Accepted Answer

The cell will shrivel due to water loss.

Question 18

Which of the following statements about defined (synthetic) media is correct?

Accepted Answer

Its exact chemical composition is known.

Question 19

Which of the following best describes the function of a chemostat?

Accepted Answer

It maintains a microbial population in a particular phase of growth.

Question 20

A scientist wants to estimate the number of bacteria in a sample using serial dilution and viable plate counts. If 0.1 mL of a $$10^{-4}$$ dilution yields 50 colonies, what is the original concentration of bacteria per mL? Use the formula $$	ext{CFU/mL} = \frac{	ext{Number of colonies}}{	ext{Volume plated (mL)} 	imes 	ext{Dilution factor}}.$$

Accepted Answer

$$	ext{CFU/mL} = \frac{50}{0.1 	imes 10$$^{-4}$$} = 5 	imes 10^6$

Microbial Nutrition and Growth: Study Notes

Guida di studio - Domande di pratica

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