During photosynthesis, six water molecules and six molecules of carbon dioxide are transformed into glucose (a carbohydrate) and six molecules of oxygen gas. Light energy from the sun powers the reaction.
Reactants in a chemical reaction are substances that are transformed during the reaction to make the products (in this case, carbohydrate and oxygen). Carbon dioxide and water are the reactants in the photosynthesis reaction.
Because carbon dioxide is transformed into a carbohydrate, the photosynthesis reaction is also a process of carbon fixation. Carbon fixation is any process which converts carbon dioxide gas into a solid.
Carbon fixation through photosynthesis creates about 176 billion tons of carbohydrate every year. According to the March 15, 2000 edition of the journal "Ecology," two-thirds of this carbohydrate is produced by phytoplankton and bacteria in the world's oceans.
According to the European Project on Ocean Acidification, rising acidity in the oceans over the next century may affect the ability of ocean phytoplankton to photosynthesize.