Chloroplasts play a crucial role in photosynthesis by capturing light energy through pigments located in their thylakoid membranes, with chlorophyll being the primary pigment involved.

Chloroplasts are the essential organelles responsible for photosynthesis, the process that converts light energy into chemical energy. These organelles are predominantly found in the cells of green plants and certain algae, giving them their characteristic green color. The process of capturing light takes place within the thylakoid membranes of chloroplasts, which are organized into structures known as grana.

The thylakoid membranes house various pigments, primarily chlorophyll a and b, that absorb light energy. These pigments are clustered into formations called photosystems. Each photosystem consists of a reaction center, where the primary photochemical reaction occurs, surrounded by numerous antenna pigment molecules. These antenna molecules capture light energy and direct it to the reaction center.

When light strikes the antenna pigments, it excites their electrons, elevating them to a higher energy state. This phenomenon is referred to as resonance energy transfer, where the excited electrons are subsequently transferred to the reaction center. At this center, an excited electron is passed to a primary electron acceptor, which triggers a series of redox reactions known as the electron transport chain.

The energy released by these electrons is utilized to pump protons across the thylakoid membrane, thereby establishing a proton gradient. This gradient is instrumental in driving the synthesis of ATP, the cell’s energy currency, through a process known as photophosphorylation. Concurrently, the electrons are eventually used to reduce NADP$^+$ to NADPH, a molecule that carries high-energy electrons to the Calvin cycle. In the Calvin cycle, these electrons contribute to the conversion of carbon dioxide into glucose.

In summary, chloroplasts are vital for capturing light energy during photosynthesis via the pigments in their thylakoid membranes. These pigments absorb light, excite their electrons, and initiate a cascade of reactions that transform light energy into chemical energy, which is stored in the form of ATP and NADPH. These high-energy molecules are then utilized in the Calvin cycle to synthesize glucose, the primary product of photosynthesis.