The structure responsible for photosynthesis in plant cells is the chloroplast. Chloroplasts contain the green pigment chlorophyll, which captures sunlight and converts it into chemical energy during photosynthesis. This process transforms carbon dioxide and water into glucose and oxygen, providing energy for the plant and ultimately forming the base of the food chain. Chloroplasts are vital for converting light energy into a usable form, not only sustaining the plant itself but also supporting life on Earth by supplying oxygen and organic compounds to other organisms.