Q: A culture starts with 1,000 cells. If the generation time is 30 minutes, 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

Which of the following best describes the chemical composition of a typical bacterial cell by dry weight?

Accepted Answer

Approximately 50% protein, 20% nucleic acids, 10% lipids, 20% polysaccharides

Question 2

A microbiologist wants to isolate a specific bacterium from a mixed sample. Which type of medium should she use to inhibit the growth of unwanted microbes while allowing the target organism to grow?

Accepted Answer

Selective medium

Question 3

Which of the following best describes aseptic technique in microbiology?

Accepted Answer

A set of procedures to prevent contamination of cultures and the environment

Question 4

Which of the following methods directly measures the number of viable bacterial cells in a culture?

Accepted Answer

Plate count method (colony-forming units)

Question 5

A bacterial culture is grown in a batch system. Which phase of the 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 6

A culture starts with 1,000 cells. If the generation time is 30 minutes, 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

Which of the following statements about continuous culture in a chemostat is correct?

Accepted Answer

Fresh medium is continuously added and culture is continuously removed to maintain a steady state

Question 8

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

Accepted Answer

Increasing susceptibility to environmental stress

Question 9

A hospital patient develops a persistent infection on a catheter. Which microbial property most likely contributes to the difficulty in treating this infection?

Accepted Answer

The bacteria have formed a biofilm on the catheter

Question 10

Which of the following alternatives to binary fission is used by some bacteria to reproduce?

Accepted Answer

Budding

Question 11

A researcher wants to distinguish between two bacterial species that look similar on a nutrient agar plate. Which type of medium should she use?

Accepted Answer

Differential medium

Question 12

Which of the following best explains why measuring turbidity with a spectrophotometer may not accurately reflect the number of viable cells in a culture?

Accepted Answer

Turbidity measures both live and dead cells, not distinguishing between them

Question 13

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

Accepted Answer

Exponential (log) phase

Question 14

A culture of E. coli is growing in a chemostat at steady state. If the dilution rate is increased beyond the maximum growth rate of E. coli, what will happen to the culture?

Accepted Answer

The culture will be washed out

Question 15

Which of the following best describes the function of an enrichment medium?

Accepted Answer

It enhances the growth of a particular microorganism over others

Question 16

A bacterial culture is in the death phase. Which of the following best describes what is happening in the culture?

Accepted Answer

The number of dying cells exceeds the number of new cells formed

Question 17

Which of the following is a key reason why biofilms are significant in medical settings?

Accepted Answer

Biofilms can protect pathogens from the host immune system and antibiotics

Question 18

A scientist is using the plate count method to estimate bacterial numbers. She dilutes her sample by a factor of $$10^{-6}$$ and plates 0.1 mL, obtaining 50 colonies. What is the original concentration of bacteria per mL?

Accepted Answer

$$5 	imes 10^8$ CFU/mL

Question 19

Which of the following best explains why batch culture eventually enters stationary phase?

Accepted Answer

Nutrients become depleted and waste products accumulate

Question 20

Which of the following is a major difference between batch and continuous culture?

Accepted Answer

Continuous culture allows for constant cell density and nutrient levels

Microbial Growth: Culturing, Measurement, and Dynamics

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