Chemotaxis is a process by which cells migrate toward higher concentrations of a signaling molecule. The signaling molecule binds cell-surface receptors that result in actin polymerization at the cell membrane. Actin polymerization results in the formulation of filamentous actin that exerts a force and leads to protrusion of the leading edge. A researcher tested Compound A on chemotaxing cells and measured the relative amount of filamentous actin found in the cells at different times. 1. Which of these structures, if present in a prokaryote, would prevent the organism from using this type of actin polymerization to chemotax toward a signal?

A. cell wall

B. flagellum

C. mitochondrion

D. ribosome

2. In the model proposed, which of these events MOST likely occurs to facilitate chemotaxis?

A. Integrins anchor the cell to extracellular components.

B. Motor proteins move actin toward the leading edge.

C. Mitochondria migrate away from the leading edge.

D. Desmosomes anchor the cell to other cells.

3. Based on the researcher’s observations on filamentous actin, what other observation regarding cell chemotaxis was MOST likely observed?

A. The cell moved toward the source of the signaling molecule only after the addition of Compound A.

B. The cell moved away from the source of the signaling molecule only after the addition of Compound A.

C. The cell first moved toward and then away from the signaling molecule after the addition of Compound A.

D. The cell did not move toward or away from the signaling molecule after the addition of Compound A.

4. The researcher hypothesizes that Compound A passively diffuses through the cell membrane to bind actin subunits. Which of these observations, if true, would MOST support his hypothesis?

A. Increasing extracellular sodium concentration interferes with Compound A function.

B. Adding actin to the extracellular medium interferes with Compound A function.

C. Reducing the temperature of the cell interferes with Compound A function.

D. Blocking ATP hydrolysis interferes with actin function.