In Calvin Cycle, carboxylation is during which carbon dioxide combines with ribulose-1,5-bisphosphate. Reduction is the second step during which carbohydrate is formed at the expense of the photochemically made ATP and NADPH. Regeneration is the third step, during which the carbon dioxide acceptor ribulose- 1,5- bisphosphate is formed and regenerated back. This is also known as the C3 cycle because the first stable product formed is three carbon compound.