Q: A food sample contains 10 bacterial cells. If the generation time is 20 minutes and the sample sits at optimal temperature for 4 hours, how many cells will be present? Use $$N_f = N_0$ \times 2^n.$$

$$N_f = 10 \times 2$$^{12}$$ = 40,960$$

Question 1

Which of the following best describes the process of binary fission in bacteria?

Accepted Answer

A single cell elongates, forms a septum, and splits into two genetically identical daughter cells.

Question 2

A batch culture of E. coli is inoculated with $$10^4$$ cells/mL. After 6 hours, the concentration is $$10^6$$ cells/mL. If the generation time is constant, how many generations have occurred? Use $$n = (\log_{10} N_f - \log_{10} N_0$)/0.301.$$

Accepted Answer

$$n = (6 - 4)/0.301 = 6.64$$ generations

Question 3

Which phase of the bacterial growth curve is characterized by cells adapting to new conditions and synthesizing new enzymes?

Accepted Answer

Lag phase

Question 4

In a chemostat, which parameter directly controls the microbial growth rate?

Accepted Answer

Flow rate of fresh medium

Question 5

A researcher needs to grow bacteria to $$5 	imes 10^8$ cells/mL for an experiment. Which method would provide the fastest and most accurate estimate of when this concentration is reached?

Accepted Answer

Measuring optical density with a spectrophotometer

Question 6

Which of the following statements about viable cell counts is TRUE?

Accepted Answer

Viable cell counts are determined by counting colony-forming units (CFUs) after plating serial dilutions.

Question 7

A food sample contains 10 bacterial cells. If the generation time is 20 minutes and the sample sits at optimal temperature for 4 hours, how many cells will be present? Use $$N_f = N_0$ 	imes 2^n.$$

Accepted Answer

$$N_f = 10 	imes 2$$^{12}$$ = 40,960$$

Question 8

Which of the following best explains why the stationary phase occurs in a batch culture?

Accepted Answer

Nutrients are exhausted or waste products accumulate, balancing cell division and death.

Question 9

Which method would be LEAST effective for counting only living bacterial cells in a sample?

Accepted Answer

Petroff-Hauser chamber without viability staining

Question 10

Which of the following best describes a facultative anaerobe?

Accepted Answer

Grows with or without oxygen, but grows better with oxygen

Question 11

Which of the following is a key advantage of continuous culture using a chemostat over batch culture?

Accepted Answer

Cells can be maintained in exponential phase indefinitely

Question 12

Which of the following is NOT a typical reason for the lag phase in bacterial growth?

Accepted Answer

Cells are dividing at their maximum rate

Question 13

Which of the following best describes the role of acylhomoserine lactone (AHL) in quorum sensing?

Accepted Answer

It is an autoinducer that diffuses across membranes and regulates gene expression in response to cell density.

Question 14

Which of the following environmental factors would NOT typically affect microbial growth?

Accepted Answer

Magnetic field strength

Question 15

A batch culture is inoculated with $$5 	imes 10^3$ cells/mL. After 5 generations, what is the final cell concentration? Use N_f$$ = $$N_0$$ 	imes 2^n$$.

Accepted Answer

$$N_f = 5 	imes 10^3$ 	imes 2^5$ = 1.6 	imes 10^5$

Question 16

Which of the following is a disadvantage of the pour plate method compared to the spread plate method?

Accepted Answer

Colonies may be variable in size and harder to count accurately.

Question 17

Which of the following best describes a biofilm?

Accepted Answer

A complex, surface-attached community of microbes embedded in a self-produced matrix

Question 18

Which of the following is a psychrophile most likely to be found?

Accepted Answer

In Antarctic sea ice at 0°C

Question 19

Which of the following statements about the measurement of bacterial growth by optical density is TRUE?

Accepted Answer

It measures the turbidity of a culture, which is proportional to the total cell number.

Microbial Growth and Its Control: Study Notes

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