Question 1

Which of the following best describes microbial growth?

Accepted Answer

An increase in cell number

Question 2

A food sample is stored at 4°C in a refrigerator. After a week, you notice slime and off-odors. Which group of microorganisms is most likely responsible for this spoilage?

Accepted Answer

Psychrotrophs

Question 3

Which of the following is a chemical requirement for microbial growth?

Accepted Answer

Nitrogen

Question 4

A bacterium is found growing in a jar with no oxygen present. It dies when exposed to air. Which term best describes this organism?

Accepted Answer

Obligate anaerobe

Question 5

Which of the following equations represents the action of catalase in detoxifying hydrogen peroxide?

Accepted Answer

$$2H_2O_2 \xrightarrow{catalase} 2H_2O + O_2$

Question 6

Why are salted fish and sweetened condensed milk resistant to microbial spoilage?

Accepted Answer

They have high osmotic pressure, causing plasmolysis in microbes

Question 7

Which of the following best explains why hyperthermophiles can survive at temperatures above 100°C near deep-sea hydrothermal vents?

Accepted Answer

Immense pressure in ocean depths prevents water from boiling

Question 8

A microbiologist wants to isolate a single bacterial species from a mixed culture. Which method should they use?

Accepted Answer

Streak plate method

Question 9

Which of the following statements about biofilms is FALSE?

Accepted Answer

Biofilms prevent the transfer of genetic information

Question 10

A bacterium is able to grow in the presence or absence of oxygen, but grows best when oxygen is present. Which term best describes this organism?

Accepted Answer

Facultative anaerobe

Question 11

Which of the following is a physical requirement for microbial growth?

Accepted Answer

Osmotic pressure

Question 12

A culture medium contains only known quantities of glucose, ammonium phosphate, sodium chloride, magnesium sulfate, potassium phosphate, and water. What type of medium is this?

Accepted Answer

Chemically defined medium

Question 13

Which of the following best describes the generation time of a bacterial population?

Accepted Answer

The time required for a cell to divide or a population to double

Question 14

Which phase of the bacterial growth curve is characterized by an equilibrium between cell division and cell death?

Accepted Answer

Stationary phase

Question 15

A sample is diluted 1:100,000 and 0.1 mL is plated, resulting in 18 colonies. What is the original concentration of bacteria per mL?

Accepted Answer

$$1.8 	imes 10^6$

Question 16

Which of the following best explains why acidophiles can infect foods such as sauerkraut and pickles?

Accepted Answer

They grow best at acidic pH below 4

Question 17

Which of the following is NOT a direct method for measuring microbial growth?

Accepted Answer

Turbidity measurement

Question 18

Which of the following best describes the role of superoxide dismutase in bacteria?

Accepted Answer

It converts superoxide radicals to hydrogen peroxide and oxygen

Question 19

Which type of medium would you use to encourage the growth of a rare bacterium present in low numbers in a soil sample?

Accepted Answer

Enrichment culture

Question 20

Which of the following statements about agar is TRUE?

Accepted Answer

It solidifies at about 50°C and is generally not metabolized by microbes

Microbial Growth: Requirements, Biofilms, and Culture Methods

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