Question 1

Which phase of the microbial growth curve is characterized by metabolic activity without an increase in cell number?

Accepted Answer

Lag phase

Question 2

During the exponential (log) phase, the population of bacteria doubles at regular intervals. If the initial population is $$N_0$$ and the number of generations is $$n$$, what is the formula for the final population $$N$$?

Accepted Answer

$$N = N_0$ 	imes 2^n$$

Question 3

Which method is best suited for counting bacteria in aquatic samples after trapping them on a membrane filter?

Accepted Answer

Microscopic count after membrane filtration and staining

Question 4

A bacterium is transferred from an old culture to a fresh medium of different composition. What is most likely to happen to the lag phase?

Accepted Answer

It will be longer

Question 5

Which environmental factor is most critical for the growth of obligate aerobes?

Accepted Answer

Presence of oxygen

Question 6

What is the main difference between the spread-plate and pour-plate methods for viable counts?

Accepted Answer

Spread-plate method allows colonies to grow only on the surface, while pour-plate allows colonies to grow both on the surface and within the agar.

Question 7

Which class of microorganisms grows optimally at pH above 8?

Accepted Answer

Alkaliphiles

Question 8

A culture of E. coli is incubated at 37°C. If its generation time is 0.35 hours, how many generations will occur in 7 hours?

Accepted Answer

20 generations

Question 9

Which phase of the growth curve is typically reached when nutrient availability becomes limiting and the number of viable cells remains constant?

Accepted Answer

Stationary phase

Question 10

Which type of microorganism would you expect to thrive in a hot spring with temperatures above 80°C?

Accepted Answer

Hyperthermophile

Question 11

If a sample contains 150 bacteria per square and the counting chamber has 25 squares, what is the total number of bacteria in the chamber?

Accepted Answer

$$150 	imes 25 = 3750$$

Question 12

Which wavelength is commonly used for measuring bacterial turbidity in spectrophotometry?

Accepted Answer

480 nm (blue)

Question 13

Which group of microorganisms can grow in the absence of oxygen but also utilize oxygen if it is present?

Accepted Answer

Facultative anaerobes

Question 14

What is the effect of extremely high NaCl concentration on most non-halophilic bacteria?

Accepted Answer

They undergo plasmolysis and stop growing

Question 15

Which phase of the microbial growth curve is associated with the accumulation of toxic waste products and loss of cell viability?

Accepted Answer

Death phase

Question 16

A sample is serially diluted 1:10 five times before plating. What is the final dilution factor?

Accepted Answer

$$10^5$$

Question 17

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

Accepted Answer

Gram staining

Question 18

Which type of microorganism would be most likely to grow in a soda lake with a pH of 10?

Accepted Answer

Alkaliphile

Question 19

If a bacterial culture starts with $$N_0 = 100$ cells and undergoes 4 generations, what is the final cell count?

Accepted Answer

$$100 	imes 2^4$ = 1600$$

Question 20

Which environmental factor is most likely to affect the cardinal temperatures for microbial growth?

Accepted Answer

Enzymatic reaction rates

Microbial Growth: Cell Cycle, Growth Curve, Measurement, and Environmental Factors

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