What Are the Reactants of Photosynthesis?

By Liz Veloz; Updated April 24, 2017
Plants use the sun's energy to make their own food.

Photosynthetic organisms use light energy from the sun to transform two reactants, carbon dioxide and water, into sugar and oxygen gas. Green plants, algae and some bacteria can perform photosynthesis and are responsible for oxygenating the Earth's atmosphere.

The Reaction

Light energy transforms six carbon dioxide molecules and six water molecules into one molecule of glucose (sugar) and six molecules of oxygen gas.

Comsumption Vs. Production

In a chemical reaction, reactants are chemical compounds that are consumed or transformed to make the products. Thus, carbon dioxide and water are the reactants in photosynthesis, and glucose and oxygen are the products.

Complementary Processes

Photosynthesis and cellular respiration are complementary reactions. Cellular respiration is the process by which most cells make energy. The products of photosynthesis, oxygen and glucose, are the reactants of the cellular respiration reaction. In turn, the products of cellular respiration, carbon dioxide and water, are the reactants in photosynthesis.

Worldwide Significance

Photosynthesis is responsible for absorbing atmospheric carbon dioxide and producing oxygen that is released into the atmosphere. Photosynthesis also creates an enormous biomass of carbohydrate (sugar) energy. Photosynthetic organisms make about 176 billion tons of carbohydrate each year.

History of the Atmosphere

Early in the planet's history, photosynthetic organisms were responsible for oxygenating the atmosphere. According to "Science News," photosynthetic organisms might have begun to oxygenate the atmosphere much earlier than was previously thought, as much as 2.7 billion years ago.

About the Author

Liz Veloz is a writer, scientist and college teacher living in Madison, Wis. Her science, travel and adventure writing has appeared in numerous literary journals and other publications. Veloz holds a doctorate in the biological sciences and a Master of Arts in English from the University of California, Davis.