Q: A researcher starts with $$N_0 = 50$ bacterial cells. If the population undergoes n = 8$ generations, what is the final population size N_t$? Use the formula N_t$$ = $$N_0$$ \times 2^n$$.

$$N_t = 50 \times 2^8$ = 12,800$$

Q: Which of the following best describes the main advantage of using agar as a solidifying agent in microbiological media?

Agar remains solid at both room temperature and $$37^\circ\text{C}$$, making it ideal for culturing pathogens.

Question 1

A hospital laboratory is trying to isolate a single species of bacteria from a mixed sample. Which technique should they use to obtain a pure culture, and what is the main reason for using this technique?

Accepted Answer

Use the streak plate method to separate individual cells, ensuring that isolated colonies arise from single cells.

Question 2

A researcher starts with $$N_0 = 50$ bacterial cells. If the population undergoes n = 8$ generations, what is the final population size N_t$? Use the formula N_t$$ = $$N_0$$ 	imes 2^n$$.

Accepted Answer

$$N_t = 50 	imes 2^8$ = 12,800$$

Question 3

Which of the following best describes the main advantage of using agar as a solidifying agent in microbiological media?

Accepted Answer

Agar remains solid at both room temperature and $$37^\circ	ext{C}$$, making it ideal for culturing pathogens.

Question 4

A bacterial culture is grown in a closed system. After a period of rapid growth, the number of viable cells plateaus and remains stable. Which phase of the bacterial growth curve is this, and what is the main reason for this stability?

Accepted Answer

Stationary phase; the rate of cell growth equals the rate of cell death due to nutrient depletion and waste accumulation.

Question 5

Which of the following best explains why biofilms are often highly resistant to antibiotics and immune responses?

Accepted Answer

Biofilms have a structured architecture with open channels that protect bacteria and limit penetration of antimicrobials.

Question 6

A scientist is culturing a bacterium that requires many amino acids and vitamins in its medium because it cannot synthesize them. What term best describes this bacterium?

Accepted Answer

Fastidious

Question 7

Which of the following scenarios best illustrates plasmolysis in bacteria?

Accepted Answer

A bacterial cell placed in a high-salt solution loses water, causing its cytoplasm to shrink away from the cell wall.

Question 8

Which of the following best distinguishes a selective medium from a differential medium?

Accepted Answer

A selective medium contains chemicals that inhibit unwanted microbes, while a differential medium contains indicators that reveal metabolic differences.

Question 9

A microbiologist is studying a bacterium that grows best at $$60^\circ	ext{C} in $$hot springs. Which temperature class does this organism belong to?

Accepted Answer

Thermophile

Question 10

Which enzyme must a bacterium possess to detoxify superoxide ($$O_2$$^-$$) radicals produced during aerobic metabolism?

Accepted Answer

Superoxide dismutase

Question 11

A bacterial species is found to grow equally well in the presence or absence of oxygen, but does not use oxygen for energy production. What is the correct classification for this organism?

Accepted Answer

Aerotolerant anaerobe

Question 12

A laboratory is using MacConkey agar to isolate bacteria from a stool sample. What properties does this medium have?

Accepted Answer

It is both selective (inhibits Gram-positive bacteria) and differential (indicates lactose fermentation).

Question 13

Which of the following best describes the difference between alpha and beta hemolysis on blood agar?

Accepted Answer

Beta hemolysis is complete lysis of red blood cells, producing a clear zone; alpha hemolysis is partial lysis, producing a greenish-brown zone.

Question 14

A scientist is culturing bacteria in a chemostat. What is the main advantage of this system compared to a closed batch culture?

Accepted Answer

It maintains the bacterial population in a constant state of exponential (log) growth.

Question 15

Which of the following best describes a photoautotroph?

Accepted Answer

An organism that uses sunlight for energy and $$CO_2 as $$its carbon source.

Question 16

A bacterium is isolated from a deep-sea hydrothermal vent and grows optimally at $$100^\circ	ext{C}. $$Which term best describes its temperature preference?

Accepted Answer

Hyperthermophile

Question 17

A bacterial colony is observed to have cells at the edge growing rapidly, while those in the center are dying. What is the most likely explanation for this observation?

Accepted Answer

Cells at the edge have better access to nutrients and oxygen, while those in the center face competition and depletion.

Question 18

Which of the following best describes a capnophile?

Accepted Answer

A microorganism that requires elevated $$CO_2$$ concentrations for growth.

Question 19

A laboratory technician needs to determine the number of living bacteria in a water sample suspected of contamination. Which method should they use and why?

Accepted Answer

Viable count, because it quantifies only living cells capable of multiplying.

Question 20

Which of the following best describes an osmotolerant bacterium?

Accepted Answer

A bacterium that can grow in high-salt environments by synthesizing small organic molecules to balance osmotic pressure.

Microbial Growth and Cultivation: Study Notes for Chapter 6

Study Guide - Practice Questions

Study Guide - Flashcards