| Feature | Primary Active Transport | Secondary Active Transport | | :--- | :--- | :--- | | | ATP | Electrochemical gradient (ion gradient) | | Indirect Energy Source | None | ATP (used earlier to create the gradient) | | Example Protein | Sodium-Potassium Pump | Sodium-Glucose Symporter | | Direction of Movement | Always "uphill" against gradient | One substance "downhill," another "uphill" |
: The cell membrane folds inward to form a pocket, engulfing external material and bringing it inside.
The driving ion and the transported molecule move in across the membrane.