Proton Gradient
The Proton Gradient is a concentration gradient of protons (H⁺ ions) across the Thylakoid membrane, with a high concentration in the Thylakoid Lumen and a lower concentration in the Stroma. This gradient is created by the activity of the Electron Transport Chain, which pumps protons into the lumen. The gradient stores potential energy that drives the synthesis of ATP through ATP Synthase.