Q: Which method would be most appropriate for counting cells in a sample with very low cell density (<10 cells/ml)?

Direct plating and colony counting

Q: A bacterial population grows from $N_0 = 500$ cells to $N_t = 8,000$ cells in 2 hours. What is the generation time ($g$)? Use $n = \log_2 \left( \frac{N_t}{N_0} \right)$ and $g = \frac{\text{total time}}{n}$.

$n = \log_2 \left( \frac{8,000}{500} \right) = 4$, $g = \frac{120}{4} = 30$ minutes

Question 1

Which of the following best describes binary fission in bacteria?

Accepted Answer

A form of cell division where a cell splits into two genetically identical daughter cells after doubling its contents.

Question 2

During which phase of the microbial growth cycle do cells prepare for active division by synthesizing new enzymes and metabolites?

Accepted Answer

Lag phase

Question 3

A bacterial culture starts with $N_0 = 1,000$ cells and grows to $N_t = 128,000$ cells in 3 hours. What is the number of generations ($n$) that occurred? Use the formula $n = \log_2 \left( \frac{N_t}{N_0} \right)$.

Accepted Answer

$n = \log_2 \left( \frac{128,000}{1,000} \right) = 7$

Question 4

Which macronutrient makes up approximately 50% of the dry weight of a microbial cell?

Accepted Answer

Polysaccharide

Question 5

What is the main difference between exponential and logistic growth in microbial populations?

Accepted Answer

Exponential growth rate remains constant regardless of population size, while logistic growth rate decreases as carrying capacity is approached.

Question 6

Which of the following is a limitation of microscopic cell counts when measuring microbial growth?

Accepted Answer

Cannot distinguish between live and dead cells without special stains.

Question 7

In a chemostat, which factor primarily determines the cell density?

Accepted Answer

Concentration of a limiting nutrient

Question 8

Which trace element is essential for the function of cytochromes and FeS proteins in electron transport?

Accepted Answer

Iron (Fe)

Question 9

A researcher wants to maintain a bacterial culture in exponential growth for several weeks. Which system should they use?

Accepted Answer

Continuous culture (chemostat)

Question 10

Which phase of the microbial growth cycle is characterized by a net decrease in cell number due to more cells dying than growing?

Accepted Answer

Death phase

Question 11

Biofilms are significant in medical settings because they:

Accepted Answer

Can cause persistent infections on medical devices.

Question 12

Which of the following best explains why generation time for bacteria is typically shorter than for eukaryotic microbes?

Accepted Answer

Bacteria have simpler cell division mechanisms and fewer cellular components to replicate.

Question 13

If the generation time ($g$) of a bacterial culture is 30 minutes and the culture is incubated for 5 hours, how many generations ($n$) have occurred? Use $n = \frac{	ext{total time}}{g}$.

Accepted Answer

$n = \frac{300}{30} = 10$

Question 14

Which of the following is NOT a step in biofilm formation?

Accepted Answer

Immediate dispersal of cells upon attachment

Question 15

Which method would be most appropriate for counting cells in a sample with very low cell density (<10 cells/ml)?

Accepted Answer

Direct plating and colony counting

Question 16

Which nutrient is critical for the synthesis of nucleic acids and phospholipids in microbial cells?

Accepted Answer

Phosphorus (P)

Question 17

A bacterial population grows from $N_0 = 500$ cells to $N_t = 8,000$ cells in 2 hours. What is the generation time ($g$)? Use $n = \log_2 \left( \frac{N_t}{N_0} ight)$ and $g = \frac{	ext{total time}}{n}$.

Accepted Answer

$n = \log_2 \left( \frac{8,000}{500} \right) = 4$, $g = \frac{120}{4} = 30$ minutes

Question 18

Which of the following statements about the stationary phase in microbial growth is correct?

Accepted Answer

Cell division and cell death rates are balanced, resulting in no net increase in cell number.

Question 19

Which of the following is a real-world consequence of biofilm formation?

Accepted Answer

Biofilms can cause dental cavities and joint infections.

Question 20

Which of the following best describes the role of the septum in bacterial cell division?

Accepted Answer

It is a structure that forms to separate the two daughter cells during binary fission.

Microbial Growth: Mechanisms, Measurement, and Dynamics

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