Question

which of the following scenarios describes movement of materials from an area of low concentration to an area of high concentration across a cell membrane?
water moving into a cell placed in a hypotonic solution.
glucose entering a cell via facilitated diffusion when its concentration is higher outside.
sodium ions being pumped out of a nerve cell.
oxygen moving from the lungs into the blood.

Explanation:

1. Osmosis (water movement in a hypotonic solution), facilitated diffusion, and simple diffusion (oxygen movement) are passive transport processes that move substances from high - to low - concentration areas.
2. Sodium - potassium pumps actively transport sodium ions out of nerve cells against their concentration gradient (from low to high concentration).

Answer:

Sodium ions being pumped out of a nerve cell.