A chloroplast is an organelle found in plant cells and other eukaryotic organisms that conduct photosynthesis. Its structure is highly adapted for this function: Outer and Inner Membranes: The chloroplast is enclosed by a double membrane envelope*, which regulates the passage of materials into and out of the organelle. Stroma: The fluid-filled space within the inner membrane is called the stroma*. It contains enzymes for the Calvin cycle (light-independent reactions), as well as ribosomes and chloroplast DNA. Thylakoids: Suspended within the stroma are numerous flattened, sac-like membranes called thylakoids*. The thylakoid membranes contain chlorophyll and other pigments, as well as electron transport chains, where the light-dependent reactions of photosynthesis occur. Grana (singular: Granum): Thylakoids are often stacked into structures called grana*. Each stack is a granum, and these stacks increase the surface area for light absorption. Stroma Lamellae: Individual grana are connected by unstacked thylakoid membranes called stroma lamellae* (or intergranal thylakoids), which ensure efficient communication and transport between the grana. This intricate structure maximizes the efficiency of photosynthesis by providing distinct compartments for the light-dependent and light-independent reactions.