Chloroplasts are cellular organelles that are located in plant cells only and are not found in animal cells. Inside the chloroplasts are thylakoid membranes that contain chlorophyll.
Chloroplasts contain two membranes that protect the inner structures of the organelle. The stroma and the stacks of thylakoid membranes are found inside of the inner membrane. The chlorophyll molecules sit inside each thylakoid membrane and capture light from the sun. The chloroplasts help catalyze the light-dependent reactions of photosynthesis because they contain high concentrations of chlorophyll. Once the light-dependent reactions are complete and the sun has gone down, the light-independent reactions begin and finish the process of photosynthesis.