Question 1

Which phase of bacterial growth in a closed batch system is characterized by a balance between cell division and cell death, resulting in no net increase in cell number?

Accepted Answer

Stationary phase

Question 2

A microbiologist is culturing bacteria in a chemostat. Which of the following best describes the main difference between a chemostat and a closed batch culture system?

Accepted Answer

A chemostat allows for continuous removal of waste and addition of nutrients, maintaining cells in log phase.

Question 3

Which of the following terms describes microorganisms that thrive in environments with high salt concentrations, such as salt lakes?

Accepted Answer

Halophiles

Question 4

A bacterium isolated from a deep-sea hydrothermal vent grows optimally at 80°C and high pressure. Which two terms best describe this organism?

Accepted Answer

Thermophile and barophile

Question 5

Which enzyme is commonly used by aerobic organisms to eliminate the reactive oxygen species superoxide ($$O_2$$^-$$)?

Accepted Answer

Superoxide dismutase

Question 6

Obligate anaerobes are unable to survive in the presence of oxygen because:

Accepted Answer

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

Question 7

Which of the following best describes the difference between phototrophs and heterotrophs?

Accepted Answer

Phototrophs use light as an energy source, while heterotrophs obtain energy from organic compounds.

Question 8

A microbiologist wants to isolate Salmonella from a stool sample. Which type of medium should be used to inhibit the growth of non-pathogenic bacteria while allowing Salmonella to grow?

Accepted Answer

Selective medium

Question 9

Which of the following is an example of a differential medium, and what does it differentiate?

Accepted Answer

MacConkey agar; differentiates lactose fermenters from non-lactose fermenters

Question 10

Which of the following is an indirect method for counting microbial cells?

Accepted Answer

Measuring turbidity using a spectrophotometer

Question 11

Which of the following terms refers to the removal of all microbial life, including endospores, from an object?

Accepted Answer

Sterilization

Question 12

A hospital technician uses an autoclave to process surgical instruments. Which physical method is being employed, and what is the primary mechanism of microbial control?

Accepted Answer

Moist heat sterilization; denaturation of proteins and destruction of membranes

Question 13

Which of the following chemical agents is most appropriate for disinfecting surfaces contaminated with Mycobacterium tuberculosis, and why?

Accepted Answer

Phenolics; they disrupt cell walls and are effective against mycobacteria

Question 14

Which of the following best describes the process of decontamination?

Accepted Answer

Reducing the number of pathogenic microorganisms to a safe level

Question 15

A laboratory technician uses filtration to sterilize a heat-sensitive solution. Which statement best explains why this method is chosen?

Accepted Answer

Filtration physically removes microorganisms without exposing the solution to high temperatures.

Question 16

Which of the following factors is most important when choosing a germicide for use in a hospital setting?

Accepted Answer

The germicide's spectrum of activity and its effectiveness against target pathogens

Question 17

A patient with a deep wound infection is treated with hydrogen peroxide. Which enzyme produced by some bacteria can neutralize this chemical, reducing its effectiveness?

Accepted Answer

Catalase

Question 18

Which of the following best explains why endospores are more resistant to chemical disinfectants than vegetative cells?

Accepted Answer

Endospores have a tough, protective coat and low metabolic activity.

Question 19

A food processing plant uses UV radiation to control microbial growth on packaging surfaces. What is the primary mechanism by which UV radiation kills microorganisms?

Accepted Answer

Formation of thymine dimers in DNA, leading to replication errors

Question 20

A researcher is testing a new disinfectant and calculates the decimal reduction time ($$D$$ value) for a bacterial population. If the initial population is $$10^6$$ cells and the $$D$$ value is 2 minutes, how many cells remain after 6 minutes of exposure?

Accepted Answer

$$10^3$$ cells

Microbial Growth, Adaptation, and Control: Study Notes

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