Question 1

Which of the following best describes a defined (synthetic) medium for culturing bacteria?

Accepted Answer

A medium with an exact, known chemical composition.

Question 2

A microbiologist wants to grow Neisseria, a fastidious organism, in the lab. Which medium should they use and why?

Accepted Answer

Chocolate agar, because it contains lysed red blood cells that provide heme and NAD.

Question 3

Which type of medium would you use to distinguish between Streptococcus pyogenes and Streptococcus pneumoniae based on their hemolytic properties?

Accepted Answer

Blood agar, because it is a differential medium.

Question 4

Which of the following statements about agar is correct?

Accepted Answer

Agar is added to broth to solidify the medium and make plates.

Question 5

A medium that allows only Gram-negative bacteria to grow and differentiates lactose fermenters from non-fermenters is best described as:

Accepted Answer

Selective and differential.

Question 6

Which of the following is a key difference between complex and defined media?

Accepted Answer

Complex media contain ingredients with unknown chemical composition.

Question 7

Why are fastidious microorganisms difficult to grow in the laboratory?

Accepted Answer

They require special nutrients not found in standard media.

Question 8

Which of the following media would be most appropriate for isolating and identifying bacteria that can completely lyse red blood cells?

Accepted Answer

Blood agar, because it allows observation of beta-hemolysis.

Question 9

A scientist wants to grow only Staphylococcus aureus from a mixed sample. Which type of medium should they use?

Accepted Answer

Selective medium, because it inhibits unwanted microbes.

Question 10

Which of the following best explains why MacConkey agar is considered both selective and differential?

Accepted Answer

It inhibits Gram-positive bacteria and differentiates lactose fermenters by color change.

Question 11

Which of the following is NOT a characteristic of enriched media?

Accepted Answer

It always has a known chemical composition.

Question 12

A researcher is culturing E. coli and wants to ensure reproducibility by using a medium with precise chemical amounts. Which medium should they choose?

Accepted Answer

Defined (synthetic) medium.

Question 13

Which ingredient in LB broth makes it a complex medium?

Accepted Answer

Yeast extract, because its exact chemical composition is unknown.

Question 14

If a medium contains tryptone and yeast extract, what type of medium is it?

Accepted Answer

Complex medium.

Question 15

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

Accepted Answer

Identifying pathogenic bacteria based on their ability to lyse red blood cells.

Question 16

A microbiologist observes colonies with different colors on a plate. What type of medium is most likely being used?

Accepted Answer

Differential medium.

Question 17

Which of the following best describes the purpose of adding agar to a medium?

Accepted Answer

To solidify the medium for the growth of colonies.

Question 18

A scientist wants to distinguish between bacteria that can ferment lactose and those that cannot. Which medium should they use?

Accepted Answer

MacConkey agar, because it is differential for lactose fermentation.

Question 19

Which of the following is a correct statement about fastidious microorganisms?

Accepted Answer

They require enriched media containing special nutrients.

Cultivation of Microbes: Media Types and Growth Requirements

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