Question 1

Which of the following best describes a biofilm?

Accepted Answer

A collection of microbes living on a surface in a complex community, often embedded in a self-produced matrix.

Question 2

Which of the following is a primary function of quorum sensing in biofilms?

Accepted Answer

To enable bacteria to communicate and coordinate gene expression based on population density.

Question 3

A hospital patient develops a catheter-associated infection that is difficult to treat with antibiotics. Which property of biofilms most likely contributes to this resistance?

Accepted Answer

Biofilms provide a protective matrix that limits penetration of microbicides and antibiotics.

Question 4

Which of the following best explains why most prokaryotes have not been grown in laboratory culture media?

Accepted Answer

Their specific nutritional and environmental requirements are unknown or difficult to replicate.

Question 5

Which type of culture medium would you use to isolate a bacterium that can grow in the presence of high salt concentrations, such as Staphylococcus aureus?

Accepted Answer

Selective medium

Question 6

A microbiologist wants to distinguish between lactose-fermenting and non-lactose-fermenting bacteria on a single plate. Which type of medium should be used?

Accepted Answer

Differential medium

Question 7

Which of the following equations correctly represents the number of cells ($$N) in a $$bacterial population after $$n$$ generations, starting from a single cell?

Accepted Answer

$$N = 2^n$$

Question 8

A bacterial culture starts with 100 cells. After 5 generations, how many cells will there be? Use the formula $$N = N_0$ 	imes 2^n$$, where $$N_0 is $$the initial number of cells and $$n is $$the number of generations.

Accepted Answer

3,200

Question 9

Which phase of the bacterial growth curve is characterized by a balance between cell division and cell death?

Accepted Answer

Stationary phase

Question 10

Which of the following best describes the function of superoxide dismutase (SOD) in aerobic bacteria?

Accepted Answer

It detoxifies superoxide radicals ($$O_2$$^-$$) by converting them to hydrogen peroxide (H_2O_2$).

Question 11

Which of the following organisms would you expect to grow at the bottom of a thioglycollate broth tube, where oxygen concentration is lowest?

Accepted Answer

Obligate anaerobes

Question 12

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

Accepted Answer

Turbidity measurement

Question 13

A bacterium is classified as a mesophile. Which temperature range would you expect it to grow best in?

Accepted Answer

20°C to 40°C

Question 14

Which of the following best explains why obligate halophiles require high salt concentrations for growth?

Accepted Answer

Their cellular enzymes and membranes require high osmotic pressure to maintain structure and function.

Question 15

Which of the following statements about agar is TRUE?

Accepted Answer

Agar liquefies at 100°C and solidifies at about 40°C.

Question 16

A microbiologist wants to culture an obligate anaerobe. Which of the following techniques would be most appropriate?

Accepted Answer

Use of a reducing medium and an anaerobic jar

Question 17

Which of the following best describes the lag phase of bacterial growth?

Accepted Answer

Cells are adjusting to a new environment and synthesizing necessary enzymes.

Question 18

Which of the following is a reason why biofilms are important in natural and clinical settings?

Accepted Answer

They dominate the structure of most natural environments and are involved in many chronic infections.

Question 19

Which of the following best distinguishes a chemically defined medium from a complex medium?

Accepted Answer

A chemically defined medium contains exact amounts of pure chemicals, while a complex medium contains extracts and digests of natural products.

Question 20

A sample of water is filtered through a membrane filter, which is then placed on a nutrient agar plate. After incubation, colonies are counted. Which method of microbial enumeration is this?

Accepted Answer

Membrane filtration

Microbial Nutrition and Growth: Colonies, Biofilms, and Environmental Requirements

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