Question 1

Which group of microorganisms is most likely to thrive in a hot spring with a temperature of $$70^\circC$$?

Accepted Answer

Thermophiles

Question 2

A food company wants to preserve fruit by adding a high concentration of sugar. Which principle explains why this inhibits microbial growth?

Accepted Answer

High sugar creates a hypertonic environment, causing water to leave microbial cells.

Question 3

Which enzyme is essential for aerobic bacteria to detoxify hydrogen peroxide ($$H_2O_2$$)?

Accepted Answer

Catalase

Question 4

A microbiologist is using a medium that contains only known quantities of glucose, ammonium chloride, and mineral salts. What type of medium is this?

Accepted Answer

Chemically defined medium

Question 5

Which of the following best describes a facultative anaerobe?

Accepted Answer

Can grow with or without oxygen, but grows better with oxygen.

Question 6

During which phase of the bacterial growth curve are cells most metabolically active and dividing at a constant rate?

Accepted Answer

Log (exponential) phase

Question 7

A microbiologist wants to isolate a single bacterial species from a mixed sample. Which technique should be used?

Accepted Answer

Streak plate method to obtain a pure culture

Question 8

Which of the following best describes the function of a selective medium?

Accepted Answer

It inhibits the growth of some organisms while allowing others to grow.

Question 9

A bacterial culture has a starting population of $$1 	imes 10^3$ cells. If the generation time is 30 minutes, how many cells will there be after 2 hours of exponential growth?

Accepted Answer

$$1.6 	imes 10^4$

Question 10

Which phase of the bacterial growth curve is characterized by the depletion of nutrients and accumulation of waste products, resulting in equal rates of cell division and cell death?

Accepted Answer

Stationary phase

Question 11

A sample is plated using the standard plate count method. After incubation, 50 colonies are counted on a plate inoculated with 0.1 mL of a $$10^{-4}$$ dilution. What is the original concentration of bacteria in the sample (in CFU/mL)?

Accepted Answer

$$5 	imes 10^6$

Question 12

Which of the following statements about direct and indirect methods of measuring microbial growth is correct?

Accepted Answer

Indirect methods, such as turbidity, estimate cell numbers based on light absorption.

Question 13

Which group of microorganisms would be most likely to cause spoilage of refrigerated foods?

Accepted Answer

Psychrophiles

Question 14

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

Accepted Answer

They lack enzymes such as superoxide dismutase and catalase to detoxify reactive oxygen species.

Question 15

A microbiologist is testing a new medium that allows only Gram-negative bacteria to grow and turns pink if lactose is fermented. This medium is best described as:

Accepted Answer

Selective and differential

Question 16

During binary fission, which of the following events occurs first?

Accepted Answer

DNA replication

Question 17

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

Accepted Answer

Cell death exceeds cell division.

Question 18

A hospital is culturing a sample from a wound infection. To ensure only the pathogen grows, which type of medium should be used?

Accepted Answer

Selective medium

Question 19

Which of the following is NOT a correct match between microorganism type and its oxygen requirement?

Accepted Answer

Aerotolerant anaerobe – cannot survive in oxygen

Question 20

A culture medium contains beef extract, peptone, and agar. Which type of medium is this?

Accepted Answer

Complex

Microbial Growth: Key Concepts and Methods

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