Transport of a compound across a cell membrane (down a concentration gradient) was measured at several concentrations. The presence or absence of ATP had no effect on the transport of this compound. Which best describes the mechanism of transport? $$\begin{array} { c c }
\text { Concentration Difference, } & \begin{array} { c }
\text { Transport Rate, } \
\mu \mathbf { m o l } / \mathbf { m i n }
\end{array} \
\hline \boldsymbol { M } & 30 \
2.5 & 60 \
5 & 100 \
10 & 175 \
25 & 200
\end{array}$$

Question

Transport of a compound across a cell membrane (down a concentration gradient) was measured at several concentrations. The presence or absence of ATP had no effect on the transport of this compound. Which best describes the mechanism of transport? $$\begin{array} { c c } 
\text { Concentration Difference, } & \begin{array} { c } 
\text { Transport Rate, } \
\mu \mathbf { m o l } / \mathbf { m i n }
\end{array} \
\hline \boldsymbol { M } & 30 \
2.5 & 60 \
5 & 100 \
10 & 175 \
25 & 200
\end{array}$$

Quizplus · Accepted Answer

Facilitated diffusion is the transport mechanism where molecules move down their concentration gradient through a membrane protein, and it does not require ATP. The transport rate increases with concentration but eventually plateaus, indicating saturation, which is characteristic of facilitated diffusion.

Transport of a Compound Across a Cell Membrane (Down a Concentration