Question

The Energetics of Coupled Transport

Sucrose concentration is higher in the cytoplasm than in the extracellular environment. Na+ concentration is higher in the extracellular environment than in the cytoplasm. Animal cells can take up sucrose against its concentration gradient using a Na+/sucrose symporter. Indicate if the following statements are true or false.
A. In the Na+/sucrose symporter, Na+ is also moving against its concentration gradient.
B. For the symporter to work, the cell must first establish a Na+ concentration gradient.
C. A symporter works by making the phospholipid bilayer more permeable to ions and sucrose.
D. Moving sucrose against its concentration gradient is a form of active transport.
E. A Na+/sucrose antiporter would be capable of moving sucrose into the cell while moving Na+ out of the cell.
F. Since the Na+/sucrose symporter exchanges a single sucrose for a single Na+, it can also be considered a uniporter

Answer 1

Step-by-step explanation:

A. False - A symporter system requires that one of the molecules to be transported using passive transport.

B. True - The Na+ will move down the established concentration gradient releasing energy to facilitate movement of sucrose against its concentration gradient. This is known as secondary active transport.

C. False - sucrose moves through ion channels not by diffusion to better control its movement across the membrane.

D. True - Movement of molecules against their concentration gradient thus requiring energy input is known as active transport.

E. False - One of the molecules needs to be moving against its concentration gradient.

F. False - A Uniporter system allows the binding and transport of a single molecule at a time. A symporter allows simultaneous binding and transport of Na+ and sucrose molecules.