A cell 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? facilitated diffusion of Ca2+ into the cell down its electrochemical gradient movement of Ca2+ into the cell through an ion channel down its concentration gradient passive diffusion of Ca2+ into the cell down its electrochemical gradient cotransport of Ca2+ into the cell with Cl- movement of Ca2+ into the cell through a carrier protein down its electrical gradient I know that the answer is 1 but please explain why. Thank you.

A cell 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?

1. facilitated diffusion of Ca²⁺ into the cell down its electrochemical gradient
2. movement of Ca²⁺ into the cell through an ion channel down its concentration gradient
3. passive diffusion of Ca²⁺ into the cell down its electrochemical gradient
4. cotransport of Ca²⁺ into the cell with Cl^-
5. ^{movement of Ca2+ into the cell through a carrier protein down its electrical gradient}

^{I know that the answer is 1 but please explain why. Thank you.}