The Calvin cycle is a process that plants and algae use to turn carbon dioxide from the air into sugar, the food autotrophs need to grow.
Every living thing on Earth depends on the Calvin cycle. Plants depend on the Calvin cycle for energy and food. Other organisms, including herbivores, also depend on it indirectly because they depend on plants for food. Even organisms that eat other organisms, such as carnivores, depend on the Calvin cycle. Without it, they wouldn't have the food, energy, and nutrients they need to survive.
It is divided into three main stages:
In this stage the carbon dioxide combines with RuBP, to be reduced and attached to an organic molecule. It forms 2 molecules of 3-PGA (3-phosphoglyceric acid). The enzyme which is used in this process to catalyse the reaction is ribulose bisphosphate carboxylase/oxygenase. The enzyme works rather slowly and processes only 3 molecules of RuBP per second. The process is called carbon fixation because carbon dioxide is fixed from an inorganic form to organic molecules.
In this step, 3-PGA (3-phosphoglyceric acid) is converted into simple sugar- G3P (Glyceraldehyde-3 phosphate). ATP and NADPH is utilized in this stage as energy sources and the energy is transferred to sugar molecules for long storage purposes.
It is the third stage of the Calvin cycle and is a complex process that requires ATP. In this stage, some of the G3P molecules are used to produce glucose, while others are recycled to regenerate the RuBP acceptor.