Question 1

Which of the following best describes the difference between defined and complex media used for culturing bacteria?

Accepted Answer

Defined media have a known exact chemical composition, while complex media contain digests of biological materials with unknown exact composition.

Question 2

A microbiologist wants to isolate a pure culture of a bacterium from a mixed sample. Which technique should they use and why?

Accepted Answer

Streak plate technique, because it allows for the isolation of single colonies derived from individual cells.

Question 3

Which of the following equations correctly expresses the number of cells ($$N_t) $$after $$n$$ generations, starting from $$N_0$$ cells?

Accepted Answer

$$N_t = N_0$ 	imes 2^n$$

Question 4

A batch culture of E. coli is inoculated with $$5 	imes 10^7$ cells. After 2 hours, the population reaches 1$$ 	imes $$10^8$$ cells. What is the generation time ($$g) in $$hours?

Accepted Answer

$$g = 2$$ hours

Question 5

Which of the following statements about binary fission in bacteria is correct?

Accepted Answer

Binary fission results in two genetically identical daughter cells, each receiving a copy of the chromosome.

Question 6

Which of the following best explains why the 'great plate count anomaly' occurs when comparing direct microscopic counts to viable plate counts in natural samples?

Accepted Answer

Many organisms in natural samples cannot grow under laboratory conditions due to unknown or unmet nutritional requirements.

Question 7

Which of the following is a key adaptation of psychrophilic microorganisms that allows them to thrive in cold environments?

Accepted Answer

Production of enzymes with more $$\alpha-$$helices and fewer $$\beta-$$sheets for increased flexibility.

Question 8

A culture medium contains eosin Y and methylene blue, which inhibit Gram-positive bacteria and distinguish lactose fermenters by colony color. This medium is best classified as:

Accepted Answer

Complex, selective, and differential

Question 9

Which of the following is the correct formula for calculating the generation time ($$g) $$from the slope of a semilogarithmic plot of microbial growth?

Accepted Answer

$$g = 0.301 / 	ext{slope}$$

Question 10

Which of the following best describes the role of compatible solutes in halophilic microorganisms?

Accepted Answer

They are synthesized or accumulated to maintain positive water balance without inhibiting cellular processes.

Question 11

Which enzyme is essential for aerobes to detoxify superoxide anion ($$O_2$$^-$$)?

Accepted Answer

Superoxide dismutase

Question 12

A bacterium isolated from a soda lake grows optimally at pH 10 and requires high salt concentrations. This organism is best described as a(n):

Accepted Answer

Haloalkaliphile

Question 13

Which of the following statements about biofilms is FALSE?

Accepted Answer

Biofilms are always composed of a single microbial species.

Question 14

Which of the following is a limitation of using turbidimetric (optical density) measurements to estimate microbial cell numbers?

Accepted Answer

Clumping or biofilm formation can cause deviations from linearity between cell number and turbidity.

Question 15

Which of the following best explains why obligate anaerobes are killed by oxygen?

Accepted Answer

They lack enzymes such as superoxide dismutase and catalase to detoxify reactive oxygen species.

Question 16

Which of the following is a correct statement about the chemostat in continuous culture?

Accepted Answer

It allows independent control of both growth rate and cell density by adjusting dilution rate and limiting nutrient concentration.

Question 17

Which of the following is a molecular adaptation found in hyperthermophilic Archaea that stabilizes their membranes at high temperatures?

Accepted Answer

Membranes composed of C40 hydrocarbons bonded by ethers to glycerol phosphate, forming a lipid monolayer.

Question 18

Which of the following best describes the function of growth factors in microbial nutrition?

Accepted Answer

They are organic compounds required in small amounts, often as coenzymes, that some microbes cannot synthesize.

Question 19

A microbiologist is culturing a marine bacterium that requires NaCl for growth. Which term best describes this organism?

Accepted Answer

Halophile

Microbial Nutrition, Growth, and Environmental Influences: Study Notes for Microbiology Students

Study Guide - Practice Questions

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