The carbon-fixing reactions
The carbon-fixing reactions used to be called the dark reactions because light does not play a direct role in their functioning. The reactions take place in series outside of the grana in the stroma of the chloroplast. These reactions only occur if the end products of the light reactions are available for use. Depending on the plant involved, the carbon-fixing reactions may develop or progress in different ways. The most common type of carbon-fixing reactions in plants is the process called the Calvin cycle. In the Calvin cycle, carbon dioxide from the atmosphere is combined with a 5-carbon sugar—RuBP, or ribulose bisphosphate. The combined molecules are converted via several steps into a 6-carbon sugar, such as glucose. The ATP and NADPH molecules from the light reactions provide the energy and resources for the reactions. Some of the sugars produced are further combined into polysaccharides (strings of simple sugars) or are stored as starch within the plant. There are other variations, including the 4-carbon pathway which is usually found in desert plants (C4 plants).