Final answer:
The subject in question refers to the light-dependent reactions of photosynthesis, where light energy is transformed into chemical energy via electron excitation and transfer across a thylakoid membrane's electron transport chain.
Step-by-step explanation:
They transform light energy to chemical energy by exciting electrons and then moving them from molecule to molecule on the thylakoid membranes. This process occurs during the light-dependent reactions of photosynthesis in the chloroplasts.
When photons strike a photosystem, pigments pass the light energy to chlorophyll molecules which then excite electrons. These electrons are passed through an electron transport chain (ETC), where the cytochrome complex plays a critical role in transferring protons across the thylakoid membrane and shifting electrons between photosystems II (PSII) and I (PSI). The energy from the excited electrons is ultimately stored in molecules like ATP and NADPH during this process, and this stored energy is used in the Calvin cycle to produce glucose.