Final answer:
The ion that creates an electrochemical gradient during photosynthesis by being pumped into the thylakoid is the proton (H+). This process occurs in the electron transport chain and leads to the production of ATP through the ATP synthase enzyme.
Step-by-step explanation:
The ion pumped into the interior of the thylakoid to create an electrochemical gradient during photosynthesis is the proton (H+). In the process of photosynthesis, the electron transport chain moves protons across the thylakoid membrane into the lumen, building up a high concentration of protons. This creates a significant pH gradient as the inside of the thylakoid space becomes more acidic compared to the stroma. The high concentration of protons inside the thylakoid lumen forms what is called a chemiosmotic or electrochemical gradient. Utilizing this gradient, the protons flow through a specialized protein channel known as ATP synthase during chemiosmosis, which generates adenosine triphosphate (ATP) by adding a phosphate group to adenosine diphosphate (ADP).