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How do chloroplast grana and stroma take part in photosynthesis?

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Underwater view of a glowing chain of tunicates with a scuba diver and boat visible near the water's surface in the background. — photochemical reaction Chain of fluorescent tunicates.

In the process of photosynthesis, the chloroplast’s internal structures—the grana and the stroma—perform distinct, specialized roles to convert light energy into chemical energy.12

The Role of Grana

The grana consist of tightly stacked thylakoids, which are the sites of the light-dependent reactions. These membranes house chlorophyll and other protein complexes that capture sunlight. When light strikes these pigments, it triggers an electron transport chain that generates ATP and NADPH, which serve as essential energy carriers for the subsequent stages of photosynthesis.12

The Role of Stroma

The stroma is a colorless, enzyme-rich matrix surrounding the thylakoids. It serves as the site for the light-independent reactions, or "dark reactions," such as the Calvin cycle. Using the ATP and NADPH produced in the grana, enzymes within the stroma—most notably rubisco—catalyze the fixation of carbon dioxide into organic compounds like carbohydrates.12