You are examining the data from two time points taken in an experiment. At time 1 there was an extracellular concentration of Na+ of 115 mM outside the cell and 8mM inside the cell. An amino acid, lycine, is at 20mM outside and 40mM inside. At the second time measured Na+ is 100mM outside the cell and 23 mM inside the cell. Lycine is 15 mM outside the cell and 45mM inside. What is the best explanation?

Question

A. Both Na+ and the amino acid bind on the side of the membrane where the Na+ concentration is higher, and both are transported to the side of the membrane where the Na+ concentration is lower.
B. Na+ and the amino acid bind to opposite sides of the membrane, and the amino acid undergoes net transport from the side of the membrane with lower Na+ concentration to the side of the membrane where the Na+ concentration is higher.
C. Both Na+ and the amino acid bind on the side of the membrane where the Na+ concentration is lowest, and undergo net movement to the other side of the membrane.
D. Both Na+ and the amino acid bind to the side of the membrane where the amino acid concentration is lower and are transported toward the side of the membrane where the amino acid concentration is higher.
E. Na+ and the amino acid bind to opposite sides of the membrane, and Na+ undergoes net transport from the side of the membrane with higher Na+ concentration toward the side with lower concentration, while the amino acid moves in the opposite direction.

Answer 1

Answer: D