The energy source in photosynthesis is light.

Here's why:

* Photosynthesis is the process plants use to convert light energy into chemical energy in the form of glucose (sugar).

* Light energy is captured by chlorophyll, a pigment found in chloroplasts within plant cells.

* This captured light energy is used to split water molecules, releasing electrons that power the production of glucose.

Let me know if you'd like to learn more about the specific steps of photosynthesis!