The part of the plant responsible for photosynthesis is primarily the leaf, specifically in the cells containing chloroplasts. In these chloroplasts, the process converts light energy from the sun into chemical energy stored in glucose. The chlorophyll pigments in leaves capture solar energy, which, combined with carbon dioxide and water, produces oxygen and glucose. This process is vital for plant growth, providing energy and organic compounds, and it also contributes oxygen to the environment, supporting life on Earth.