1. In active transport, energy is used to move a solute against its concentration gradient. For each molecule of ATP used, 2 K + are pumped into the cell and 3 Na + are pumped out of the cell. Outside of cell Inside of cell Na + K+K+ Sodium– potassium pump Figure 5.13 Primary Active Transport: The Sodium–Potassium Pump

2. 1. 3 Na + and 1 ATP bind to the protein “pump.” Extracellular space Cytoplasm K+K+ ATP Na + Figure 5.13 Primary Active Transport: The Sodium-Potassium Pump

3. 2. ADP is released, causing a change in the pump’s shape. Extracellular space Cytoplasm K+K+ ADP PiPi Figure 5.13 Primary Active Transport: The Sodium-Potassium Pump

4. 3. 3 Na+ are released as 2 K+ bind to the pump. Extracellular space Cytoplasm PiPi Figure 5.13 Primary Active Transport: The Sodium-Potassium Pump

5. 4. P i is released, causing the pump’s shape to change, and releasing 2 K + Extracellular space Cytoplasm PiPi K+K+ Figure 5.13 Primary Active Transport: The Sodium-Potassium Pump