Q: Given the bacterial growth equation $$N_t = N_0$(2^n)$$, if you start with $$N_0 = 500$ cells and after 4 generations you have N_t$ cells, what is N_t$?

$$N_t = 500 \times 2^4$ = 8,000$$

Question 1

Which of the following best describes the relationship between the fungus and the photosynthetic partner in lichens?

Accepted Answer

Mutualism, where both the fungus and the photosynthetic partner benefit.

Question 2

A patient’s blood sample is collected for microbial culture. Which of the following best describes the type of medium that should be used to maximize the recovery of fastidious pathogens?

Accepted Answer

Enriched medium

Question 3

Which of the following is a key feature of biofilms that distinguishes them from planktonic bacteria?

Accepted Answer

Biofilms form as a result of quorum sensing and produce an extracellular matrix.

Question 4

A microbiologist wants to isolate a pure culture from a mixed sample. Which technique is most appropriate?

Accepted Answer

Streak plate method

Question 5

Which of the following best describes a selective medium?

Accepted Answer

A medium that contains substances that inhibit the growth of some organisms while allowing others to grow.

Question 6

Given the bacterial growth equation $$N_t = N_0$(2^n)$$, if you start with $$N_0 = 500$ cells and after 4 generations you have N_t$ cells, what is N_t$?

Accepted Answer

$$N_t = 500 	imes 2^4$ = 8,000$$

Question 7

A microbiologist performs a serial dilution and plates 0.1 mL of a $$10^{-5}$$ dilution, resulting in 75 colonies. What is the concentration of bacteria in the original sample?

Accepted Answer

$$7.5 	imes 10^6$ CFU/mL

Question 8

Which phase of batch microbial growth is characterized by cells adjusting to a new environment and not dividing rapidly?

Accepted Answer

Lag phase

Question 9

Which of the following best describes the function of a Gas-Pak jar in microbiology?

Accepted Answer

It removes oxygen to create anaerobic conditions for culturing anaerobes.

Question 10

Which of the following is an example of a differential medium?

Accepted Answer

MacConkey agar, which distinguishes lactose fermenters from non-fermenters.

Question 11

A culture medium contains 1 g glucose, 16.4 g $$Na_2HPO_4$$, 1.5 g $$KH_2PO_4$$, 2 g $$(NH_4$)_3PO_4$$, 0.2 g $$MgSO_4$$ \cdot 7H_2O$$, 0.01 g $$CaCl_2$$, and 0.005 g $$FeSO_4$$ \cdot 7H_2O$$ per liter. What type of medium is this?

Accepted Answer

Defined (synthetic) medium

Question 12

Which method would be most appropriate for counting only live bacterial cells in a sample?

Accepted Answer

Viable plate count after serial dilution

Question 13

Which of the following best describes the stationary phase of batch microbial growth?

Accepted Answer

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

Question 14

A microbiologist wants to distinguish between bacteria that can completely lyse red blood cells and those that cannot. Which medium should be used?

Accepted Answer

Blood agar

Question 15

Which of the following is a correct equation for calculating the number of generations ($$n) in a $$bacterial culture, given the initial and final cell numbers?

Accepted Answer

$$n = \frac{\log N_t - \log N_0$}{\log 2}$$

Question 16

Which of the following best describes commensalism?

Accepted Answer

One organism benefits, the other is unaffected.

Question 17

A sample is diluted 1:100,000 and 0.1 mL is plated, resulting in 45 colonies. What is the original concentration of bacteria?

Accepted Answer

$$4.5 	imes 10^6$ CFU/mL

Question 18

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

Accepted Answer

Turbidity measurement

Question 19

Which of the following best explains why most prokaryotes have never been grown in a culture medium?

Accepted Answer

They require complex interactions with other organisms or specific environmental conditions not replicated in the lab.

Microbial Nutrition and Growth: Symbiosis, Biofilms, Culturing, and Measurement

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