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 chemical composition, while complex media contain ingredients of unknown composition such as yeast extract or peptone.

Question 2

A microbiologist wants to isolate a Gram-negative, lactose-fermenting bacterium from a mixed sample. Which medium should she use and what result would indicate a positive lactose fermenter?

Accepted Answer

She should use EMB agar; a positive lactose fermenter will produce dark purple colonies with or without a green metallic sheen.

Question 3

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

Accepted Answer

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

Question 4

A batch culture of E. coli is inoculated with $$1 	imes 10^6$ cells. After 3 hours, the population reaches 8$$ 	imes $$10^7$$ cells. What is the generation time ($$g) in $$minutes? Use $$g = t/n$$ and $$n = (\log N_t - \log N_0$)/\log 2.$$

Accepted Answer

30 minutes

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 direct microscopic counts of environmental samples often reveal more cells than viable plate counts?

Accepted Answer

Many microbes in natural samples cannot grow on laboratory media due to specific nutrient requirements.

Question 7

Which adaptation would you expect to find in the cytoplasmic membrane of a psychrophilic bacterium?

Accepted Answer

A high proportion of unsaturated and short-chain fatty acids to maintain membrane fluidity at low temperatures.

Question 8

A culture medium contains 10% NaCl. Which type of microorganism is most likely to grow in this medium?

Accepted Answer

An extreme halophile

Question 9

Which of the following is a function of superoxide dismutase in aerobic microorganisms?

Accepted Answer

It converts superoxide anion ($$O_2$$^-$$) to hydrogen peroxide (H_2O_2$) and oxygen (O_2$).

Question 10

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

Accepted Answer

They help maintain positive water balance by accumulating highly water-soluble molecules that do not interfere with cellular processes.

Question 11

A researcher is using a chemostat to grow a bacterial culture. Which parameter can she control independently to regulate both the growth rate and cell density?

Accepted Answer

Dilution rate and concentration of limiting nutrient

Question 12

Which of the following is a key reason why biofilms are problematic in medical and industrial settings?

Accepted Answer

Biofilms provide a protective matrix that prevents harmful chemicals and antibiotics from reaching cells deep within the structure.

Question 13

Which of the following equations correctly relates the specific growth rate ($$k) to $$the generation time ($$g$$)?

Accepted Answer

$$k = 0.693 / g$$

Question 14

Which of the following best describes the cardinal temperatures for a microorganism?

Accepted Answer

The minimum, optimum, and maximum temperatures at which an organism can grow.

Question 15

A facultative anaerobe is inoculated into thioglycolate broth. Where would you expect to see growth?

Accepted Answer

Throughout the tube, but most dense near the top where oxygen is highest.

Question 16

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

Accepted Answer

Turbidity measurements cannot distinguish between live and dead cells.

Question 17

Which of the following best explains why the viable plate count is expressed as colony-forming units (CFU) rather than the actual number of viable cells?

Accepted Answer

Some bacteria form clusters or filaments, so one colony may arise from multiple cells.

Question 18

Which of the following is a correct statement about the effect of pH on microbial growth?

Accepted Answer

Most microorganisms maintain their cytoplasmic pH near neutrality, even if the external pH is very acidic or alkaline.

Question 19

Which of the following is a molecular adaptation found in hyperthermophilic Archaea that allows their membranes to remain stable at high temperatures?

Accepted Answer

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

Microbial Nutrition, Growth, and Environmental Influences: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards