Question 1

A food company wants to preserve pickles by adding salt. Which principle explains why high salt concentrations inhibit microbial growth in this scenario?

Accepted Answer

They increase osmotic pressure, causing water to leave microbial cells.

Question 2

Which organism would be most likely to thrive in a salt mine with extremely high NaCl concentrations?

Accepted Answer

Obligate halophile

Question 3

A scientist is studying bacteria that grow optimally at $$15^\circ \mathrm{C}. $$What term best describes these organisms?

Accepted Answer

Psychrophile

Question 4

Primary producers in hydrothermal vent ecosystems utilize which energy source for growth?

Accepted Answer

Hydrogen sulfide

Question 5

Chemoautotrophs and photoautotrophs obtain their carbon from which molecule?

Accepted Answer

Carbon dioxide

Question 6

Some bacteria can convert atmospheric nitrogen ($$N_2) $$into ammonia ($$NH_3) $$for cellular use. What is this process called?

Accepted Answer

Nitrogen fixation

Question 7

A bacterium grows in the presence of oxygen but can also survive without it. What is the correct classification for this organism?

Accepted Answer

Facultative anaerobe

Question 8

Which type of microorganism is killed by exposure to atmospheric oxygen?

Accepted Answer

Obligate anaerobe

Question 9

Hydrogen peroxide ($$H_2O_2) is $$toxic to cells. Which enzyme catalyzes its breakdown into water and oxygen?

Accepted Answer

Catalase

Question 10

A microbiologist wants to graph bacterial population growth over time. Which scale is most appropriate for visualizing exponential growth?

Accepted Answer

Logarithmic (semi-logarithmic)

Question 11

During which phase of the bacterial growth curve is there intense metabolic activity but no increase in cell number?

Accepted Answer

Lag phase

Question 12

Which of the following is NOT a reason why exponential bacterial growth stops?

Accepted Answer

Bacteria becoming dormant

Question 13

In the stationary phase of bacterial growth, what is the relationship between cell death and cell formation?

Accepted Answer

The number of microbial deaths is equal to the number of new cells formed.

Question 14

A laboratory technician wants to isolate a specific bacterium from a mixed sample. Which type of medium should be used to suppress unwanted bacteria and encourage growth of the desired microbe?

Accepted Answer

Selective media

Question 15

Microbes that are introduced into a culture medium to initiate growth are called:

Accepted Answer

Inoculum

Question 16

To grow bacteria on a solid medium, which substance is commonly added to the medium?

Accepted Answer

Agar

Question 17

A culture medium made of extracts from yeasts, meat, or plants is classified as:

Accepted Answer

Complex

Question 18

A spectrophotometer is used in microbiology labs to measure which property of a bacterial culture?

Accepted Answer

Turbidity

Question 19

A measured volume of bacterial suspension is placed within a defined area on a microscope slide to count cells. What is this method called?

Accepted Answer

Direct microscope count

Question 20

A researcher wants to ensure that plates contain 30 to 300 colonies for accurate counting. Which process should be used?

Accepted Answer

Serial dilution

Question 21

Which technique is best for measuring the growth of filamentous organisms such as molds?

Accepted Answer

Dry weight

Question 22

If a single bacterial cell divides every generation, how many cells will be present after 10 generations? Use the formula $$N = N_0$ 	imes 2^n$$, where $$N_0 = 1$ and n = 10$.

Accepted Answer

1024

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