Chapter 10: 24P (page 320)
Kidney cells contain a channel that allows intracellular ammonia to exit the cells. (a) Why did researchers originally believe that cells had no need for such a channel? (b) What is the free energy source for ammonia transport via the channel? (c) The same kidney cells also contain a proton pump that expels H+ from the cells. What is the free energy source for this pump, and how does its action prevent ammonia from moving back into the kidney cells?
Short Answer
In solution (a), the cells do not need such a channel because ammonia is an uncharged molecule that can pass through the membrane.
Similarly, in solution (b), the free source for ammonia transport is passive mediated transport.
Then, in solution (c), the proton pump is an ATP-dependent pump, and it prevents ammonium into the cell because is an ionic polar molecule.