Final answer:
Charged particles like Na+ and K+ move across membranes through ion channels, driven by diffusion and the concentration gradients of the ions.
Step-by-step explanation:
The movement of charged particles, such as Na+ and K+, across cell membranes is facilitated by ion channels. These channel proteins allow specific ions to pass through the membrane while protecting them from the hydrophobic interior.
Na+ and K+ ions move down their concentration gradients through ion channel proteins, driven by the process of diffusion. However, there are differences in the driving force between Na+ and K+, which is determined by their concentration gradients and the electrochemical gradient established by the cell.