Final answer:
The energy needed for secondary active transport comes from the electrochemical gradient created by ATP-dependent primary active transport. Substances like amino acids and glucose enter the cell using this energy, which is also involved in ATP production in the mitochondria.
Step-by-step explanation:
In secondary active transport, the energy needed for the movement of molecules is most often obtained from the electrochemical gradient established by primary active transport. The primary active transport system moves ions across a cell membrane creating a charge difference that is directly dependent on ATP, thereby laying the groundwork for secondary active transport mechanisms. Through these secondary mechanisms, substances like amino acids and glucose can enter the cell and ATP itself is produced using a hydrogen ion gradient in the mitochondria.
Therefore, secondary active transport leverages the potential energy stored in the concentration differences and membrane potential created by primary active transport to move substances against their concentration gradient without directly using ATP. This type of transport is a critical component of cellular function, including nutrient uptake and the generation of energy.