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?

Hydrogen ions from split water accumulate inside the thylakoid, creating a concentration gradient. As they flow out through ATP synthase, that flow provides energy to add a phosphate group to ADP and make ATP. So the correct choice is “They flow out of the thylakoid, providing energy to add a phosphate group to ADP.”

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