Q: If an E. coli population doubles every 20 minutes, how many cells will there be after 2 hours starting from a single cell? Use the formula $$N = N_0$ \times 2$$^{n}$$, where n$ is the number of generations.

$$N = 1 \times 2$$^{6}$$ = 64$$ cells

Q: A culture is in the log phase of growth. If you start with $$10^3$$ cells and the generation time is 30 minutes, how many cells will there be after 2 hours? Use $$N = N_0$ \times 2$$^{n}$$.

$$N = 10^3$ \times 2$$^{4}$$ = 16,000$$ cells

Question 1

Which process is depicted in the first image, and what is its significance in bacterial population growth?

Accepted Answer

Binary fission; it is the primary method by which bacteria reproduce and increase their population.

Question 2

If an E. coli population doubles every 20 minutes, how many cells will there be after 2 hours starting from a single cell? Use the formula $$N = N_0$ 	imes 2$$^{n}$$, where n$ is the number of generations.

Accepted Answer

$$N = 1 	imes 2$$^{6}$$ = 64$$ cells

Question 3

During which phase of the bacterial growth curve is the population size constant due to a balance between cell division and cell death?

Accepted Answer

Stationary phase

Question 4

Which method would be most appropriate for measuring bacterial contamination in a municipal water supply, and why?

Accepted Answer

Membrane filtration, because it can concentrate and detect small numbers of bacteria from large volumes of water.

Question 5

A researcher uses a spectrophotometer to measure the turbidity of a bacterial culture. What is the relationship between absorbance and bacterial concentration?

Accepted Answer

Absorbance increases as bacterial concentration increases.

Question 6

Which of the following is NOT a direct method for measuring bacterial growth?

Accepted Answer

Dry weight

Question 7

Why might the generation time of E. coli in the human gut differ from that in a laboratory setting?

Accepted Answer

Environmental conditions such as pH, temperature, and nutrient availability differ between the gut and the lab.

Question 8

A culture is in the log phase of growth. If you start with $$10^3$$ cells and the generation time is 30 minutes, how many cells will there be after 2 hours? Use $$N = N_0$ 	imes 2$$^{n}$$.

Accepted Answer

$$N = 10^3$ 	imes 2$$^{4}$$ = 16,000$$ cells

Question 9

Which phase of the bacterial growth curve is characterized by intense metabolic activity but no increase in cell number?

Accepted Answer

Lag phase

Question 10

A scientist wants to estimate the number of viable bacteria in a yogurt sample. Which method should they use and why?

Accepted Answer

Plate count, because it only counts living cells capable of forming colonies.

Question 11

Which indirect method of measuring bacterial growth would be most affected by the presence of non-living material in the sample?

Accepted Answer

Turbidity

Question 12

Why is the stationary phase important in industrial microbiology processes such as antibiotic production?

Accepted Answer

Cells are most metabolically active and produce secondary metabolites like antibiotics during the stationary phase.

Question 13

Which of the following best describes the death phase of a bacterial growth curve?

Accepted Answer

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

Question 14

A researcher measures the amount of lactic acid produced by a bacterial culture to estimate growth. Which method is this?

Accepted Answer

Metabolic activity

Question 15

Which scenario would most likely result in an underestimation of bacterial numbers using the plate count method?

Accepted Answer

Some bacteria are viable but non-culturable under the conditions used.

Question 16

Which method would be best for counting bacteria in a milk sample that contains both live and dead cells, and why?

Accepted Answer

Microscopic count, because it counts all cells regardless of viability.

Question 17

A culture is removed from its medium, dried, and weighed. What is this method called, and what does it measure?

Accepted Answer

Dry weight; it measures the total mass of cells present.

Question 18

Which of the following is a limitation of using turbidity to estimate bacterial growth?

Accepted Answer

It cannot distinguish between live and dead cells.

Question 19

Why is generation time important in clinical microbiology?

Accepted Answer

It helps predict how quickly an infection can spread and informs treatment strategies.

Microbial Nutrition & Growth: Measuring Bacterial Population Growth

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