Question

A cell has a membrane potential of -­‐100mV (more negative inside than outside) and has 1000 times more calcium ions outside the cellthan inside. Which of the following describes the electrical and chemical gradients that influence the movement of calcium across the plasma membrane of this cell that is permeable to calcium?
A) The chemical gradient favors and the electrical gradient opposes the entry of calcium into the cell.
B) The electrical gradient favors and the chemical gradient opposes the entry of calcium into the cell.
C) Both the chemical and the electrical gradients oppose calcium entry into the cell.
D) Both thechemical and the electrical gradients favor calcium entry into the cell.

Answer 1

Answer:

D) Both chemical and the electrical gradients favor calcium entry into the cell.

Explanation:

Naturally chemical gradient drives the movement of the chemical species, in this case Ca, from the regions of higher concentration to the regions of lower concentration. Then, Ca moves to inside the cell.  

Whereas the movement due to electrical potential gradients is  from higher to lower potentials for positive charges (negative charge move in opossite direction from lower to higher potentials). Calcium is a cation, it is positively charged $(Ca^{2+})$, so calcium would move to lower potentials, that is to more negative potentials. Then Ca moves to inside the cell.