Q: A bacterial culture has a generation time of 30 minutes. If you start with 1,000 cells, how many cells will there be after 3 hours of exponential growth? Use the formula $N = N_0 \times 2^n$, where $n$ is the number of generations.

$N = 1,000 \times 2^6 = 64,000$

Question 1

A hospital patient develops a urinary tract infection caused by bacteria that thrive at body temperature ($37^\circ$C) and neutral pH. Which of the following best describes the temperature and pH classification of these bacteria?

Accepted Answer

They are mesophiles and neutrophiles.

Question 2

Which of the following best explains why obligate anaerobes are unable to survive in the presence of oxygen?

Accepted Answer

They lack enzymes such as superoxide dismutase and catalase to detoxify reactive oxygen species.

Question 3

A microbiologist is culturing bacteria in a medium with a pH of 5.0. After 24 hours, the bacterial population decreases significantly. Which of the following is the most likely explanation?

Accepted Answer

The bacteria are neutrophiles and cannot tolerate acidic conditions.

Question 4

Which of the following best describes a chemoheterotroph?

Accepted Answer

An organism that uses organic compounds as both an energy and carbon source.

Question 5

Which of the following is NOT a function of biofilms in microbial communities?

Accepted Answer

Increasing susceptibility to environmental stress.

Question 6

A bacterial culture has a generation time of 30 minutes. If you start with 1,000 cells, how many cells will there be after 3 hours of exponential growth? Use the formula $N = N_0 	imes 2^n$, where $n$ is the number of generations.

Accepted Answer

$N = 1,000 	imes 2^6 = 64,000$

Question 7

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

Accepted Answer

Log (exponential) phase

Question 8

Which of the following methods would be most appropriate for estimating the number of viable bacteria in a sample of drinking water?

Accepted Answer

Plate count method

Question 9

A researcher is studying a bacterium that can grow in the presence or absence of oxygen, but grows better with oxygen. What is the best classification for this organism?

Accepted Answer

Facultative anaerobe

Question 10

Which of the following best explains why refrigeration slows the spoilage of food by microorganisms?

Accepted Answer

Low temperatures decrease the rate of enzymatic reactions in most microbes.

Question 11

Which of the following is a chemical requirement for microbial growth that is a major component of nucleic acids and ATP?

Accepted Answer

Phosphorus

Question 12

A culture medium contains glucose, ammonium chloride, magnesium sulfate, and water. Which type of organism would be able to grow in this medium?

Accepted Answer

Chemoheterotroph

Question 13

Which of the following statements about binary fission is correct?

Accepted Answer

Binary fission results in the formation of genetically identical daughter cells.

Question 14

A bacterial population is in stationary phase. Which of the following best describes what is happening at this stage?

Accepted Answer

The rate of cell division equals the rate of cell death.

Question 15

Which of the following is a physical requirement for microbial growth that affects the ability of cells to maintain osmotic balance?

Accepted Answer

Osmotic pressure

Question 16

A patient with a chronic lung infection is found to have bacteria embedded in a thick, slimy matrix attached to lung tissue. Which of the following best explains the clinical significance of this finding?

Accepted Answer

The bacteria are forming a biofilm, which increases resistance to antibiotics and host defenses.

Question 17

Which of the following best describes the lag phase of microbial growth?

Accepted Answer

Cells are metabolically active but not dividing.

Question 18

A laboratory technician wants to estimate the number of bacteria in a culture by measuring the turbidity of the culture using a spectrophotometer. Which of the following is a limitation of this method?

Accepted Answer

It cannot distinguish between live and dead cells.

Question 19

Which of the following best explains why biofilms are a concern in medical device infections?

Accepted Answer

Biofilms protect bacteria from antibiotics and immune responses, making infections difficult to treat.

Question 20

A bacterial culture is growing in a medium with limited nitrogen. Which of the following cellular processes will be most directly affected?

Accepted Answer

Protein synthesis

Microbial Growth: Key Concepts and Study Guidance

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