Carbon dioxide is a one-carbon compound with formula CO2 in which the carbon is attached to each oxygen atom by a double bond. A colourless, odourless gas under normal conditions, it is produced during respiration by all animals, fungi and microorganisms that depend directly or indirectly on living or decaying plants for food. It has a role as a solvent, a vasodilator agent, an anaesthetic, an antagonist, a member of greenhouse gas, a human metabolite, a member of food packaging gas, a food propellant, a refrigerant, a Saccharomyces cerevisiae metabolite, an Escherichia coli metabolite and a mouse metabolite. It is a one-carbon compound, a gas molecular entity and a carbon oxide.