Light energy transforms six carbon dioxide molecules and six water molecules into one molecule of glucose (sugar) and six molecules of oxygen gas.
Photosynthesis occurs inside cells called chloroplasts in plants. Chloroplasts are full of a green pigment called chlorophyll, which is designed to absorb sunlight.
Photosynthesis takes place on the microscopic scale, but produces enormous amounts of carbohydrate (sugar), which is then available to other living organisms. Photosynthetic organisms make about 176 billion tons of carbohydrate every year.
Photosynthesis is the complementary reaction to cellular respiration, the reaction by which most cells use oxygen to transform carbohydrate energy into the form of energy that cells can use to perform work. Carbon dioxide is a byproduct of cellular respiration, and photosynthesis helps balance the atmospheric carbon dioxide produced by cellular respiration.
Early in the planet's history there was almost no oxygen in the atmosphere. According to "Science News," photosynthetic organisms may have begun to oxygenate the atmosphere as much as 3.46 billion years ago.