AP BIOLOGY

Detailed explanation-1: -The sodium-potassium pump transports sodium out of and potassium into the cell in a repeating cycle of conformational (shape) changes. In each cycle, three sodium ions exit the cell, while two potassium ions enter.

Detailed explanation-2: -However, the concentrations of these ions are maintained at constant disequilibrium, indicating that there is a compensatory mechanism moving Na+ outward against its concentration gradient and K+ inward. This mechanism is the sodium-potassium pump.

Detailed explanation-3: -Sodium ions (Na+) are attracted to the inside of neurons at rest by two forces. The high concentration of (Na+) outside the cell pushes this ion into the cell down the concentration gradient. Likewise, the electrostatic pressure due to the negative charge within the neuron attracts the positively charged (Na+) inside.

Detailed explanation-4: -Sodium uptake in the proximal tubule allows the co-transport of solutes such as glucose, phosphate, and amino acids. Sodium crosses the basolateral membrane by the action of NaK-ATPase, which transfers three sodium ions out of the cell in exchange for the inward movement of two extracellular potassium ions.