The concentration of sodium on the inside of the cell is 20 mM . The outside of the cell has a sodium concentration of 115 mM . Which mechanism of ion uptake would best move sodium from the inside of the cell to the outside? osmosis passive transport active transport

To determine the best mechanism for moving sodium from the inside of the cell (20 mM) to the outside (115 mM), we need to consider the concentration gradient and the nature of the transport mechanisms. 1. **Osmosis**: This is the movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. Osmosis does not directly involve the movement of sodium ions. 2. **Passive Transport**: This process allows substances to cross membranes without the need for energy, moving down their concentration gradient (from high to low concentration). In this case, sodium would move from outside (115 mM) to inside (20 mM), which is the opposite of what we want. 3. **Active Transport**: This mechanism requires energy (usually in the form of ATP) to move substances against their concentration gradient (from low to high concentration). In this scenario, active transport would move sodium from the inside (20 mM) to the outside (115 mM), which is the desired direction. Given these considerations, the best mechanism for moving sodium from the inside of the cell to the outside is **active transport**.