A striking feature of living cells is a marked difference between the composition of the cytosol and the extracellular milieu. Which of the following statement(s) concerning the mechanisms of maintenance of these differences is/are true?
A. The cell membrane is able to maintain a 10,000 fold gradient between the extracellular concentration of ionized calcium and the intracellular concentration
B. The key to these differences is the fact that the plasma membrane is normally impermeable to sodium, potassium and calcium
C. The selectivity of biologic membranes is highly consistent and seldom changes
D. The selectivity of cell membranes relates only to ions and not organic compounds
Answer:A
A striking feature of living cells is a marked difference between the composition of the cytosol and the extracellular milieu. Which of the following statement(s) concerning the mechanisms of maintenance of these differences is/are true?
A. The cell membrane is able to maintain a 10,000 fold gradient between the extracellular concentration of ionized calcium and the intracellular concentration B. The key to these differences is the fact that the plasma membrane is normally impermeable to sodium, potassium and calcium C. The selectivity of biologic membranes is highly consistent and seldom changes D. The selectivity of cell membranes relates only to ions and not organic compounds