1. In most cells, there are electrochemical gradients of many ions across the plasma membrane even though there are usually only one or two electrogenic pumps present in the membrane. The gradients of the other ions are most likely accounted for by
A) ion channels.
B) cotransport proteins.
C) carrier proteins.
D) B and C only
E) A, B, and C
2. What mechanisms do plants use to load sucrose produced by photosynthesis into specialized cells in the veins of leaves?
A) an electrogenic pump
B) a contransport protein
C) a proton pump
D) A and C only
E) A, B, and C
3. The sodium-potassium pump in animal cells requires cytoplasmic ATP to pump ions across the plasma membrane. When the proteins of the pump are first synthesized in the rough ER, what side of the ER membrane will the ATP binding site be on?
A) It will be on the side facing the interior of the ER.
B) It could be facing in either direction because the orientation of proteins is scrambled in the
Golgi apparatus.
C) It will be on the cytoplasmic side of the ER.
D) It doesn't matter, because the pump is not active in the ER.