Here's how it works:

* Sunlight contains energy in the form of photons.

* Chlorophyll, a green pigment found in plants, absorbs these photons.

* The absorbed light energy is used to split water molecules (H₂O) into hydrogen ions (H+) and oxygen (O₂).

* This energy is also used to convert carbon dioxide (CO₂) into sugars, which the plant uses for growth and energy.

So, in a nutshell, sunlight is the primary source of energy for photosynthesis.