Which step of the calvin cycle would be affected first by a lack of nadph?

Reduction

Reduction is the second step of the Calvin cycle which would be affected first by a lack of NADPH.

The Calvin cycle is the group of chemical processes that occur within the chloroplasts during photosynthesis . The three main steps in Calvin cycle are carbon fixation (Carboxylation), reduction, and regeneration of the starting molecule. In the reduction step, NADPH acts as a reducing agent which functions by transferring electrons that allow carbohydrates to be synthesized from carbon dioxide. During these step, there is transfer of two electrons and one proton to the phosphorylated compound by NADPH which produces one phosphate group to form the triose phosphates.

the way that the mass of carbon can be conserved through cellular respiration is through a process/law called the law of conservation of mass which even tho it undergoes a process, mass is not be destroyed or changed