Question 1

Which of the following best describes a biofilm?

Accepted Answer

A collection of microbes living on a surface in a complex community.

Question 2

A bacterium is placed in a solution with a higher concentration of solutes outside the cell than inside. What is the most likely outcome?

Accepted Answer

The cell will undergo plasmolysis as water leaves the cell.

Question 3

Which type of microorganism grows best at moderate temperatures, such as human body temperature ($37^\circ$C)?

Accepted Answer

Mesophiles

Question 4

Obligate anaerobes are killed by the presence of oxygen. What is the main reason for this sensitivity?

Accepted Answer

They lack enzymes to neutralize toxic forms of oxygen.

Question 5

Which of the following media would you use to differentiate between lactose fermenting and non-lactose fermenting bacteria?

Accepted Answer

MacConkey agar

Question 6

A halophilic organism is most likely to thrive in which environment?

Accepted Answer

A high-salt environment such as a salt flat

Question 7

Which of the following statements about binary fission is correct?

Accepted Answer

It results in the formation of two genetically identical daughter cells.

Question 8

A bacterium has a generation time of 30 minutes. If you start with 1 cell, how many cells will there be after 3 hours, assuming ideal conditions and no cell death? Use the formula $N = N_0 	imes 2^n$, where $N_0$ is the initial number of cells and $n$ is the number of generations.

Accepted Answer

$N = 1 	imes 2^6 = 64$

Question 9

Which of the following is a direct method for estimating microbial population size that does NOT require incubation?

Accepted Answer

Microscopic counts using a cell counter

Question 10

Why is refrigeration used for storing microbial cultures?

Accepted Answer

It slows down metabolic activity, allowing short-term storage.

Question 11

Which of the following best describes a selective medium?

Accepted Answer

A medium that contains substances favoring or inhibiting the growth of particular microorganisms.

Question 12

A patient sample is collected and transported to the laboratory for analysis. Which type of medium should be used to ensure the sample is not contaminated and remains viable during transport?

Accepted Answer

Transport media

Question 13

Which of the following organisms can fix atmospheric nitrogen, making it available for other life forms?

Accepted Answer

Certain bacteria

Question 14

Which phase of the bacterial growth curve is characterized by rapid cell division and exponential increase in population size?

Accepted Answer

Log (exponential) phase

Question 15

A spectrophotometer is used to measure the turbidity of a bacterial culture. What does increased turbidity indicate?

Accepted Answer

A greater bacterial population

Question 16

Which of the following is true regarding obligate intracellular pathogens such as viruses?

Accepted Answer

They can only be cultured within living cells.

Question 17

Which of the following best explains why Listeria monocytogenes is a concern in food safety?

Accepted Answer

It survives in a variety of environmental conditions, including refrigeration.

Question 18

Which of the following is a reason why aseptic technique is critical when inoculating culture media?

Accepted Answer

To prevent contamination of the media with unwanted organisms.

Question 19

Which of the following statements about complex media is correct?

Accepted Answer

The exact chemical composition is unknown.

Question 20

A chemostat is used in industrial microbiology to maintain a microbial population in which phase of growth?

Accepted Answer

Log (exponential) phase

Microbial Nutrition and Growth: Key Concepts and Requirements

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