Question 1

Which type of microorganism is most likely to cause food spoilage in a refrigerator, and what is its optimum growth temperature?

Accepted Answer

Psychrotrophs; optimum growth at $$20^{\circ}C$ to 30$$^{\circ}$$C$$

Question 2

A bacterial cell is placed in a solution containing 10% NaCl. What will most likely happen to the cell?

Accepted Answer

The cell will undergo plasmolysis as water leaves the cell.

Question 3

Which enzyme is responsible for converting hydrogen peroxide ($$H_2O_2) $$into water and oxygen in aerobic bacteria?

Accepted Answer

Catalase

Question 4

Why are hyperthermophiles that grow at temperatures above $$100^{\circ}C$ seemingly limited to oceanic depths?

Accepted Answer

Because oceanic depths provide high pressure that prevents water from boiling at $$100^{\circ}C$

Question 5

Which type of media would you use to grow obligate anaerobes, and what chemical does it contain to remove oxygen?

Accepted Answer

Reducing media; contains sodium thioglycolate

Question 6

A patient develops an infection after a catheter is inserted. The bacteria are found to be growing in a biofilm. Which property of biofilms most likely contributed to the persistence of the infection?

Accepted Answer

Biofilms shelter bacteria from harmful environmental factors and increase resistance to microbicides.

Question 7

Which of the following best describes the growth pattern of obligate aerobes in a tube of solid growth medium?

Accepted Answer

Growth occurs only where oxygen is present, typically at the top of the tube.

Question 8

Which phase of the bacterial growth curve is characterized by intense metabolic activity but little or no increase in cell number?

Accepted Answer

Lag phase

Question 9

A bacterial culture is growing in a medium with limited nutrients. After a period of rapid growth, the number of new cells equals the number of dying cells. Which phase is the culture in?

Accepted Answer

Stationary phase

Question 10

If a bacterial population doubles every 30 minutes, how many cells will there be after 3 hours if you start with 1 cell? Use the formula $$N = 2^n$$, where $$n is $$the number of generations.

Accepted Answer

64 cells

Question 11

Which of the following is a chemical requirement for microbial growth that is used as the structural backbone of organic molecules?

Accepted Answer

Carbon

Question 12

Which type of microorganism would you expect to find growing in acidic environments, such as those found in sauerkraut or pickles?

Accepted Answer

Acidophiles

Question 13

A laboratory technician needs to distinguish between colonies of different microbes on the same plate. Which type of media should be used?

Accepted Answer

Differential media

Question 14

Which biosafety level (BSL) requires workers to wear 'space suits' with an air supply and is used for highly infectious airborne pathogens?

Accepted Answer

BSL-4

Question 15

Which method is most appropriate for measuring the number of bacteria in a water sample when the concentration is very low?

Accepted Answer

Filtration method

Question 16

Which of the following statements about agar is correct?

Accepted Answer

Agar solidifies at about $$40^{\circ}C$ and is generally not degraded by microbes.

Question 17

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

Accepted Answer

Turbidity measurement

Question 18

A microbiologist wants to isolate a pure culture from a mixed sample. Which method should be used?

Accepted Answer

Streak plate method

Question 19

Which of the following best explains why a bacterial colony does not grow to fill the entire Petri plate?

Accepted Answer

The colony is limited by nutrient availability and accumulation of waste products.

Question 20

Which of the following is a real-world application of using selective media?

Accepted Answer

Suppressing unwanted microbes to isolate Salmonella Typhi using bismuth sulfite agar.

Microbial Growth: Physical and Chemical Requirements, Culture Methods, and Growth Measurement

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