Question 1

Which of the following best describes the structure of a bacterial flagellum?

Accepted Answer

A helical filament composed of flagellin, anchored by a basal body that spans the cell envelope, and powered by a rotary motor.

Question 2

During chemotaxis, what is the primary difference between a 'run' and a 'tumble' in bacterial movement?

Accepted Answer

A 'run' is a period of straight movement due to counterclockwise flagellar rotation, while a 'tumble' is a reorientation event caused by clockwise rotation.

Question 3

Which of the following is NOT a form of bacterial motility?

Accepted Answer

Endocytosis

Question 4

A researcher is measuring chemotaxis in E. coli by placing a capillary tube filled with an attractant in a bacterial suspension. Which result would indicate positive chemotaxis?

Accepted Answer

A higher concentration of bacteria accumulates inside the capillary tube compared to the surrounding medium.

Question 5

Which statement best explains the concept of a 'biased random walk' in bacterial chemotaxis?

Accepted Answer

Bacteria increase the length of their runs and decrease the frequency of tumbles when moving toward higher concentrations of an attractant.

Question 6

Which of the following best describes the energy source for flagellar rotation in most bacteria?

Accepted Answer

The proton motive force ($$\Delta p) $$across the cytoplasmic membrane.

Question 7

A mutant bacterium is unable to adapt to persistent high concentrations of an attractant. Which process is most likely defective?

Accepted Answer

Methylation and demethylation of chemoreceptors, which allows adaptation to sustained stimuli.

Question 8

Which of the following scenarios best illustrates chemotaxis in a clinical context?

Accepted Answer

Pathogenic bacteria moving toward higher concentrations of nutrients released from damaged host tissues.

Question 9

Which equation best represents the relationship between the proton motive force and the energy available for flagellar rotation?

Accepted Answer

$$\Delta G = -nF\Delta p$$

Question 10

A bacterium is observed to move away from a region of high pH toward a region of neutral pH. This behavior is best described as:

Accepted Answer

pH taxis (a form of chemotaxis)

Question 11

Which of the following is a key difference between swimming and gliding motility in bacteria?

Accepted Answer

Swimming requires flagella, while gliding does not involve flagella.

Question 12

A bacterium exhibits increased tumbling frequency when exposed to a repellent. What is the likely effect on its movement?

Accepted Answer

It will move away from the repellent in a less directed manner due to frequent reorientations.

Question 13

Which of the following best describes the process of flagellar synthesis in bacteria?

Accepted Answer

Flagellin subunits are transported through the hollow core of the flagellum and added to the tip.

Question 14

In a laboratory experiment, a bacterium is placed in a gradient of oxygen. It accumulates at intermediate oxygen concentrations. This behavior is best described as:

Accepted Answer

Aerotaxis

Question 15

Which of the following statements about adaptation in chemotaxis is correct?

Accepted Answer

Adaptation allows bacteria to reset their sensory system after prolonged exposure to a stimulus, enabling them to detect new changes in concentration.

Question 16

A patient is infected with a bacterium that lacks functional flagella. Which of the following is most likely impaired in this bacterium?

Accepted Answer

Ability to move toward or away from chemical gradients (chemotaxis)

Question 17

Which of the following best explains how bacteria sense changes in signal concentration during chemotaxis?

Accepted Answer

By comparing current receptor occupancy to past occupancy, allowing detection of temporal changes in concentration.

Question 18

A bacterium is placed in a uniform environment with no chemical gradients. What is the expected pattern of movement?

Accepted Answer

Random runs and tumbles with no net directionality.

Question 19

Which of the following is a method commonly used to measure chemotaxis in the laboratory?

Accepted Answer

Capillary tube assay, where the accumulation of bacteria in a tube containing attractant is quantified.

Question 20

A bacterium is observed to move toward a light source. This behavior is best described as:

Accepted Answer

Phototaxis

Microbial Motility and Chemotaxis

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