Q: A microbiologist is culturing a bacterium that doubles every 30 minutes. If she starts with 1 cell and after 3 hours has 64 cells, what is the generation time, and which formula supports your answer?

Generation time is 30 minutes, using $$\text{Generation\ time} = \frac{\text{Growth\ time}}{\text{Number\ of\ generations}}$$

Question 1

A microbiologist is culturing a bacterium that doubles every 30 minutes. If she starts with 1 cell and after 3 hours has 64 cells, what is the generation time, and which formula supports your answer?

Accepted Answer

Generation time is 30 minutes, using $$	ext{Generation\ time} = \frac{	ext{Growth\ time}}{	ext{Number\ of\ generations}}$$

Question 2

Which phase of the bacterial growth curve is characterized by a balance between cell division and cell death, resulting in no net increase in cell number?

Accepted Answer

Stationary phase

Question 3

A bacterium isolated from a hot spring thrives at pH 2. Which term best describes this organism?

Accepted Answer

Acidophile

Question 4

Which of the following best describes a facultative anaerobe?

Accepted Answer

It can grow in the presence or absence of oxygen.

Question 5

A researcher wants to isolate Gram-negative bacteria that can ferment lactose. Which medium should she use and why?

Accepted Answer

EMB agar, because it selects for Gram-negative bacteria and differentiates lactose fermenters.

Question 6

Which of the following statements about binary fission is correct?

Accepted Answer

It results in two genetically identical daughter cells.

Question 7

A scientist is working with a bacterium that grows best at 37°C and is commonly found in the human body. What is the best classification for this organism?

Accepted Answer

Mesophile

Question 8

Which type of media would you use if you want to distinguish between bacteria that can ferment mannitol and those that cannot, and what is a key ingredient in this medium?

Accepted Answer

MSA, which contains high salt and mannitol.

Question 9

A culture medium is prepared with exact amounts of glucose, ammonium sulfate, and magnesium chloride. What type of medium is this?

Accepted Answer

Defined medium

Question 10

During which phase of the bacterial growth curve are cells most susceptible to antibiotics that target cell wall synthesis, and why?

Accepted Answer

Log phase, because cells are actively dividing and synthesizing new cell walls.

Question 11

A laboratory technician uses a streak plate method to isolate colonies. What is the primary purpose of this technique?

Accepted Answer

To obtain pure cultures by separating individual cells.

Question 12

Which of the following best describes a chemotroph?

Accepted Answer

An organism that obtains energy from chemical compounds.

Question 13

A bacterium is found growing in a salt lake with a NaCl concentration of 20%. What is the best term to describe this organism?

Accepted Answer

Halophile

Question 14

A student is preparing media to grow a fastidious bacterium but does not know its exact nutritional requirements. Which type of media should she use?

Accepted Answer

Complex media

Question 15

Which of the following best explains why aseptic technique is critical in microbiology laboratories?

Accepted Answer

It prevents contamination of cultures and the environment.

Question 16

A bacterium is unable to grow in the presence of oxygen. Which term best describes this organism?

Accepted Answer

Obligate anaerobe

Question 17

Which of the following scenarios best illustrates the use of differential media?

Accepted Answer

A medium that changes color when bacteria ferment a specific sugar.

Question 18

A microbiologist is studying a bacterium that uses sunlight as its energy source. What is the correct classification for this organism?

Accepted Answer

Phototroph

Question 19

A culture medium contains peptone, beef extract, and agar, but the exact chemical composition is unknown. What type of medium is this?

Accepted Answer

Complex medium

Question 20

A patient sample is streaked onto MSA. After incubation, yellow colonies appear. What does this indicate about the bacteria?

Accepted Answer

They can ferment mannitol and tolerate high salt.

Fundamentals of Microbial Growth and Cultivation

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