Question 1

Which of the following best describes a chemoheterotroph in terms of its energy and carbon sources?

Accepted Answer

Uses organic compounds as both an energy source and a carbon source.

Question 2

A microbiologist wants to isolate a pure culture of a bacterium from a mixed sample. Which plating method is most appropriate for obtaining isolated colonies?

Accepted Answer

Quadrant streak plate method

Question 3

Which of the following best defines 'selective media'?

Accepted Answer

Media that contains agents to inhibit the growth of certain microbes while allowing others to grow.

Question 4

A hospital lab technician needs to sterilize heat-sensitive plastic syringes. Which sterilization method is most appropriate?

Accepted Answer

Gas sterilization with ethylene oxide

Question 5

Which of the following statements about moist heat sterilization is correct?

Accepted Answer

It kills microorganisms by denaturing proteins and disrupting membranes.

Question 6

A researcher is comparing the effectiveness of two disinfectants. Disinfectant A has a decimal reduction time ($$D-$$value) of 2 minutes, while Disinfectant B has a $$D-$$value of 5 minutes. What does this indicate?

Accepted Answer

Disinfectant A kills 90\% of bacteria in less time than Disinfectant B.

Question 7

Which of the following is NOT a characteristic of an ideal disinfectant?

Accepted Answer

It should be corrosive to metals.

Question 8

A culture medium that changes color when bacteria ferment lactose is best described as:

Accepted Answer

Differential

Question 9

Which of the following best explains why trace metals are required in bacterial growth media?

Accepted Answer

They are required as enzyme cofactors for metabolic reactions.

Question 10

A laboratory is using UV radiation to sterilize surfaces. Which property of UV light is most responsible for its antimicrobial effect?

Accepted Answer

It causes the formation of thymine dimers in DNA.

Question 11

Which of the following best describes the relationship between wavelength ($$\lambda) $$and frequency ($$f) of $$electromagnetic radiation?

Accepted Answer

As $$\lambda$$ increases, $$f$$ decreases.

Question 12

A sample is sterilized using an autoclave at 121$$^\circC $$for 15 minutes. Which principle allows the autoclave to achieve sterilization at this temperature?

Accepted Answer

Increasing the pressure raises the boiling point of water, allowing higher temperatures.

Question 13

Which of the following is the best definition of 'thermal death time'?

Accepted Answer

The time required to kill all microorganisms in a sample at a given temperature.

Question 14

A scientist is using membrane filtration to sterilize a solution. What is the main mechanism by which this method removes microorganisms?

Accepted Answer

Physical exclusion based on pore size

Question 15

Which of the following best describes the process of lyophilization?

Accepted Answer

Drying by freezing and reducing pressure to remove water by sublimation

Question 16

A bacterial colony on an agar plate is described as 'opaque, raised, with irregular margins, and rough texture.' Which term refers to the 'raised' aspect?

Accepted Answer

Elevation

Question 17

Which of the following is an example of a differential medium?

Accepted Answer

MacConkey agar, which distinguishes lactose fermenters by color change

Question 18

A solution is treated with a chemical that inhibits bacterial growth but does not kill the bacteria. Which term best describes this effect?

Accepted Answer

Bacteriostasis

Question 19

Which of the following best explains why boiling is not a reliable method for sterilization?

Accepted Answer

Boiling does not kill all bacterial spores.

Question 20

A laboratory technician is asked to prepare a chemically defined medium. Which of the following best describes this type of medium?

Accepted Answer

A medium in which the exact chemical composition is known.

Bacterial Culturing and Sterilization: Study Guide

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