The chloroplast inside the green leaves of plants is the ‘workshop’ where photosynthesis takes place. Water is supplied to the leaves by the roots, and carbon dioxide is absorbed from the air through tiny pores on the lower side of the leaf. Both these are broken down into the elements hydrogen (H), carbon (C), and oxygen (O) with the help of chlorophyll and sunlight. Plants build ‘glucose’ (grape sugar) from these elements and oxygen is released in the atmosphere as a by-product. Photosynthesis has been the source of oxygen in the air since the origin of life on the Earth.