Biology The Light Reactions

The Light Reactions

• Light energy is converted into chemical energy through the light reactions of photosynthesis. A pigment molecule absorbs a photon of light, which excites an electron in the pigment molecule to a higher energy level.

• This excitation energy is transmitted to a reaction center where it drives the transfer of an electron from chlorophyll to a molecule in the electron transport chain. As the electron moves through the transport chain, protons are pumped into the lumen of the thylakoids.

• In this Lesson, we’ll learn how electrons reduce NADP, and how ATP is synthesized when the protons exit the lumen. Reduced NADP (NADPH) and ATP contain chemical energy that’s used to synthesize carbohydrates from carbon dioxide in the light-independent, or dark, reactions of photosynthesis.