BIOL 1201 Chapter : Chapter 7 Biology Homework Notes
Document Summary
The concentration gradient of na+ ions across the membrane (higher na+ concentration outside) facilitates the diffusion of na+ into the cell. At the same time, the electrical gradient across the membrane (excess positive charge outside) drives na+ into the cell. The concentration gradient of k+ ions across the membrane (higher k+ concentration inside) facilitates the diffusion of k+ out of the cell. However, the electrical gradient across the membrane (excess positive charge outside) impedes the diffusion of k+ out of the cell. The electrochemical gradient for an ion is the sum of the concentration (chemical) gradient and the electrical gradient (charge difference) across the membrane. For na+ ions, diffusion through the na+ channel is driven by both the concentration gradient and the electrical gradient. But for k+ ions, the electrical gradient opposes the concentration gradient. Therefore, the electrochemical gradient for na+ is greater than the electrochemical gradient for k+.
