During photosynthesis, the energy from sunlight is used to split water molecules. What happens to the hydrogen ions that are split from the water molecules? They flow out of the thylakoid, providing energy to add a phosphate group to ADP. They build up in the thylakoid, providing energy to break apart ATP molecules. They build up in the thylakoid, where they bond to each other to create ATP. They flow out of the thylakoid, where they stimulate enzymes to break apart ATP.