Acell has a membrane potential of -100 mv (more negative inside than outside) and has 1,000 times more calcium ions outside the cell than inside. which best describes a mechanism by which ca²⁺ enters this cell?
a. facilitated diffusion of ca²⁺ into the cell down its electrochemical gradient
b. movement of ca²⁺ into the cell through an ion channel down its concentration gradient
c. passive diffusion of ca²⁺ into the cell down its electrochemical gradient
d. cotransport of ca²⁺ into the cell with cl⁻
e. movement of ca²⁺ into the cell through a carrier protein down its electrical gradient