Question 1

Which of the following best describes quorum sensing in bacteria?

Accepted Answer

A process where bacteria communicate using chemicals they release and detect in their environment.

Question 2

What is the primary function of quorum sensing chemicals in a bacterial biofilm?

Accepted Answer

To enable bacteria to coordinate group behaviors such as toxin production or enzyme synthesis.

Question 3

Which of the following statements is TRUE regarding the effect of quorum sensing on bacterial gene expression?

Accepted Answer

Quorum sensing changes the expression of genes already present in the bacterial DNA.

Question 4

A biofilm contains three types of bacteria: A, B, and C. Bacterium A releases a quorum sensing chemical that signals others to produce a toxin. Bacterium B has the gene for the toxin but it is turned off, while Bacterium C lacks the gene entirely. What is the likely outcome?

Accepted Answer

Only B will start producing the toxin; C cannot produce it.

Question 5

Why do bacteria in a biofilm typically wait until the population is dense before releasing quorum sensing chemicals?

Accepted Answer

Because the chemicals are only effective at high concentrations, which occur at high population densities.

Question 6

Which of the following is NOT a possible outcome of quorum sensing in bacteria?

Accepted Answer

Permanent mutation of the bacterial genome.

Question 7

Streptococcus mutans uses quorum sensing to help form dental biofilms. What is a real-world consequence of this process?

Accepted Answer

It attracts other bacteria to join the biofilm, contributing to dental plaque and cavities.

Question 8

Which of the following best explains why a bacterium must already have the gene for a trait (such as toxin production) in its core DNA to respond to a quorum sensing signal?

Accepted Answer

Quorum sensing signals can only activate existing genes, not create new ones.

Question 9

In a hospital setting, why might doctors restrict flowers for patients in intensive care, based on knowledge of Pseudomonas species and biofilms?

Accepted Answer

Pseudomonas from flowers can join biofilms and share antibiotic resistance with other bacteria, increasing infection risk.

Question 10

Which of the following equations best represents the threshold concept for quorum sensing chemical release, where $N$ is the number of bacteria and $N_c$ is the critical population density?

Accepted Answer

$N \geq N_c \implies$ quorum sensing chemicals are released

Question 11

Which of the following is a potential disadvantage for bacteria when releasing quorum sensing chemicals in a host body?

Accepted Answer

It can attract immune cells such as macrophages to the site of infection.

Question 12

A researcher observes that a bacterial population does not produce toxins until the population reaches $10^6$ cells. What is the most likely explanation?

Accepted Answer

Toxin production is triggered by quorum sensing chemicals that accumulate only at high cell densities.

Question 13

Which of the following scenarios best illustrates the difference between a change in DNA expression and a mutation?

Accepted Answer

A bacterium turns on a gene for enzyme production in response to a quorum sensing signal, but the DNA sequence remains unchanged.

Question 14

Which of the following is a correct statement about the role of quorum sensing in antibiotic resistance among Pseudomonas species?

Accepted Answer

Quorum sensing allows Pseudomonas to share its antibiotic resistance with other bacteria in the biofilm.

Question 15

If a bacterium in a biofilm receives a quorum sensing signal to make a flagellum but lacks the necessary genes, what will happen?

Accepted Answer

It will not make a flagellum because the ability is not present in its core DNA.

Question 16

Which of the following best describes the relationship between quorum sensing and biofilm formation?

Accepted Answer

Quorum sensing promotes biofilm formation by coordinating group behaviors and attracting new bacteria.

Question 17

A patient develops a persistent infection with a biofilm-forming bacterium. Which property of quorum sensing most likely contributes to the difficulty in treating this infection?

Accepted Answer

Quorum sensing allows bacteria to coordinate defense mechanisms, such as increased resistance to antibiotics, once a critical population is reached.

Bacteria and Quorum Sensing: Communication in Biofilms

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