Question 1

Which phase of microbial growth is characterized by the number of cells in the population remaining constant, with no net increase or decrease in cell number?

Accepted Answer

Stationary phase

Question 2

A culture of bacteria is growing in a flask. The number of cells doubles every 20 minutes. If you start with 12 cells, how many cells will there be after 1 hour?

Accepted Answer

$12 	imes 2^3 = 96$

Question 3

Which of the following best describes a differential medium?

Accepted Answer

A medium that distinguishes between different types of microbes based on their biological characteristics

Question 4

Blood agar is an example of which type of medium?

Accepted Answer

Differential

Question 5

A flask (Flask A) contains yeast cells in glucose-minimal salts broth incubated at $30^\circ$C aerobically. Flask B is identical except it is grown anaerobically. Which culture will produce more ATP?

Accepted Answer

Flask A

Question 6

Which of the following best explains why most microbes cannot grow in candy?

Accepted Answer

The osmotic pressure is too high for most microbes to be able to grow on it

Question 7

Organisms that are indifferent to the presence of oxygen are called:

Accepted Answer

Aerotolerant anaerobes

Question 8

Which of the following best describes a mesophile?

Accepted Answer

An organism that grows best at temperatures between $35-40^\circ$C

Question 9

When a microbe is presented with multiple carbon sources, it will generally:

Accepted Answer

Utilize the one that yields the fastest log growth first, preserving the others for later

Question 10

Which of the following enzymes would you expect to find in an obligate aerobe?

Accepted Answer

Catalase and superoxide dismutase (SOD)

Question 11

A culture of yeast is grown in two flasks: Flask A is incubated aerobically, Flask B anaerobically. Which flask will produce more alcohol?

Accepted Answer

Flask B

Question 12

Which of the following best describes a selective medium?

Accepted Answer

A medium that inhibits the growth of some microbes while allowing others to grow

Question 13

Which of the following is NOT a mechanism by which temperature can prevent microbial growth in food?

Accepted Answer

Low temperature increases osmotic pressure

Question 14

Which of the following best explains why E. coli can grow rapidly in the human intestine?

Accepted Answer

The temperature and pH are optimal for E. coli growth

Question 15

Which of the following is a characteristic of facultative anaerobes?

Accepted Answer

They can grow with or without oxygen

Question 16

A microbe that grows best at refrigerator temperatures (around $4^\circ$C) is classified as a:

Accepted Answer

Psychrophile

Question 17

Which of the following best describes the log (exponential) phase of microbial growth?

Accepted Answer

Cells are dividing at a constant, maximum rate

Question 18

Which of the following is a reason why TSA (tryptic soy agar) is not considered a selective medium?

Accepted Answer

It allows the growth of many non-fastidious microbes

Question 19

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

Accepted Answer

The number of cells decreases as more cells die than are produced

Question 20

Which of the following is a likely reason why some oral bacteria grow poorly on TSA but well on blood agar?

Accepted Answer

They are fastidious and require additional nutrients found in blood

Microbial Growth: Key Concepts, Media, and Oxygen Requirements

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