Q: A sample is plated using the spread plate method, and 234 colonies are counted on a plate from a $$10^{-6}$$ dilution. What is the original cell concentration in CFU/mL?

$$2.34 \times 10$$^{8}$$ CFU/mL

Question 1

Which of the following best describes microbial growth in the context of microbiology?

Accepted Answer

An increase in cell number, primarily by binary fission

Question 2

A microbiologist wants to culture a marine bacterium that requires sodium ions for growth. Which cation is most critical for this organism?

Accepted Answer

Na$$^+$$

Question 3

Which of the following is a key difference between defined and complex media?

Accepted Answer

Defined media have an exact chemical composition known

Question 4

A culture is diluted by transferring 1 mL into 9 mL of diluent, and this process is repeated six more times. What is the final dilution factor?

Accepted Answer

$$10^{-7}$$

Question 5

Which phase of the microbial growth curve is characterized by maximum metabolic activity and highest sensitivity to antibiotics?

Accepted Answer

Exponential (log) phase

Question 6

A sample is plated using the spread plate method, and 234 colonies are counted on a plate from a $$10^{-6}$$ dilution. What is the original cell concentration in CFU/mL?

Accepted Answer

$$2.34 	imes 10$$^{8}$$ CFU/mL

Question 7

Which of the following best explains why biofilms are a significant problem in medical settings?

Accepted Answer

Biofilms are more resistant to antibiotics and form on medical devices

Question 8

Which group of microbes would be most likely to grow in a high-sugar environment such as honey?

Accepted Answer

Osmophiles

Question 9

What is the primary function of superoxide dismutase in aerobic microbes?

Accepted Answer

To detoxify reactive oxygen species (ROS)

Question 10

Which of the following statements about autoclaving is correct?

Accepted Answer

It sterilizes by using steam at 121°C, 15 psi, for 15 minutes

Question 11

A bacterium that grows optimally at pH 9.0 is classified as a(n):

Accepted Answer

Alkaliphile

Question 12

Which of the following best describes the function of compatible solutes in microbial cells?

Accepted Answer

They prevent water loss in high-salt or dry environments without disrupting metabolism

Question 13

Which of the following is a trace metal required for electron transport in microbes?

Accepted Answer

Iron (Fe)

Question 14

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 15

A researcher measures the optical density (OD) of a bacterial culture to estimate cell number. What must be done to accurately relate OD to cell concentration?

Accepted Answer

Use a standard curve relating OD to CFU

Question 16

Which of the following best describes the difference between binary fission and budding?

Accepted Answer

Binary fission results in equal division; budding results in unequal division

Question 17

Which of the following is NOT a function of phosphorus in microbial cells?

Accepted Answer

Component of cysteine and methionine

Question 18

Which of the following statements about the great plate count anomaly is correct?

Accepted Answer

Many microbes grow in nature but cannot grow on lab media, so plate counts underestimate actual numbers

Question 19

Which of the following best describes the role of catalase in aerobic bacteria?

Accepted Answer

It breaks down hydrogen peroxide into water and oxygen

Question 20

Which of the following statements about mesophiles is correct?

Accepted Answer

They grow optimally at 20–45°C, which includes most human pathogens

Microbial Growth and Its Control: Essential Concepts and Methods

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