Q: A bacterium divides by binary fission every 30 minutes. If you start with 1 cell, how many cells will there be after 3 hours? Use the formula $$N = N_0$ \times 2^n$$, where $$n is $$the number of generations.

There will be $$N = 1 \times 2^6$ = 64$$ cells.

Question 1

Which of the following best describes the difference between microbial growth in a laboratory batch culture and in nature?

Accepted Answer

Microbial growth in laboratory batch cultures is typically uniform and predictable, whereas in nature, environmental conditions fluctuate and limit growth.

Question 2

A bacterium divides by binary fission every 30 minutes. If you start with 1 cell, how many cells will there be after 3 hours? Use the formula $$N = N_0$ 	imes 2^n$$, where $$n is $$the number of generations.

Accepted Answer

There will be $$N = 1 	imes 2^6$ = 64$$ cells.

Question 3

Which stage of bacterial growth in a closed batch system is characterized by rapid cell division and exponential increase in cell number?

Accepted Answer

Log (exponential) phase

Question 4

A mesophile is most likely to thrive at which temperature range?

Accepted Answer

Between $$20^{\circ}C$ and 45$$^{\circ}$$C$$

Question 5

Which term describes microbes that grow best at pH values below 5, and what adaptation might they use to survive in acidic environments?

Accepted Answer

Acidophiles; they pump protons out of the cell to maintain internal pH.

Question 6

Which of the following best describes a halophile's strategy for surviving in high-salt environments?

Accepted Answer

They accumulate compatible solutes to balance osmotic pressure.

Question 7

Which class of microbes would be most likely to cause infections in humans, based on their temperature preferences?

Accepted Answer

Mesophiles

Question 8

Which oxygen requirement class describes microbes that can grow in the presence or absence of oxygen, but grow better with oxygen?

Accepted Answer

Facultative anaerobes

Question 9

Which of the following is an essential nutrient for microbial growth, and how does it differ from a growth factor?

Accepted Answer

Phosphorus; it is required in large amounts and can be obtained from the environment, while a growth factor must be supplied because the cell cannot synthesize it.

Question 10

Which type of media would you use to distinguish between two bacterial species based on their ability to ferment lactose?

Accepted Answer

Differential media

Question 11

A clinical sample is collected for anaerobic culture. Which method would best ensure the survival of anaerobic microbes during transport?

Accepted Answer

Using a reducing agent in the transport medium to remove oxygen.

Question 12

Which term describes a chemical that kills microbes on inanimate surfaces, and which term describes a chemical that inhibits microbial growth on living tissue?

Accepted Answer

Disinfectant; antiseptic

Question 13

If a heat treatment reduces a bacterial population by 90% every 2 minutes, what is the decimal reduction time ($$D$$ value)?

Accepted Answer

$$D = 2$$ minutes

Question 14

Which method would be most appropriate for sterilizing heat-sensitive medical equipment?

Accepted Answer

Filtration through a $$0.22 \mu m$$ membrane

Question 15

Which level of germicide activity is required for equipment that enters sterile body sites, such as surgical instruments?

Accepted Answer

High-level

Question 16

Which factor should be considered when selecting a germicide for hospital use?

Accepted Answer

The type of microbes present and the level of contamination

Question 17

Which of the following would be most resistant to standard disinfection procedures?

Accepted Answer

Bacterial endospores

Question 18

A streak plate technique is used in the laboratory. What is its primary purpose?

Accepted Answer

To isolate individual colonies from a mixed culture

Question 19

Which method is considered a direct cell enumeration technique?

Accepted Answer

Counting colonies on an agar plate

Question 20

A phototroph and a chemotroph are grown in identical media. Which statement best describes their energy sources?

Accepted Answer

Phototrophs use sunlight for energy, while chemotrophs use chemical compounds.

Fundamentals of Microbial Growth and Decontamination

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