Carbon dioxide
From The School of Biomedical Sciences Wiki
Carbon dioxide is a chemical compound consisting of two oxygen atoms covalently linked to a central carbon atom, and so can be represented with the chemical formula CO2.
Carbon dioxide is essential for the process of photosynthesis which occurs in the chloroplasts of plants. This is a process in which the carbon dioxide from the air (around 0.0360% of the air is carbon dioxide[1]: produced by respiration by living organisms, as well as by the combustion of fossil fuels, is utilised by the plants to produce the sugars they require to grow. Plants may also store this sugar in the form of starch.
Carbon dioxide is constantly recycled in a cycle, being produced by respiration and used in photosynthesis.