Cellular respiration. is essentially the reverse of photosynthesis

In terms of the net reactants and products, yes, cellular respiration is the reverse of photosynthesis. 
Cellular respiration: Glucose and oxygen are used to make ATP, carbon dioxide, and water.
Photosynthesis: ATP, carbon dioxide, and water are used to make glucose and oxygen.

However, their pathways are NOT the reverse of each other. The enzymes involved are vastly different for each, so only the net reaction is the "reverse."

They use the si unit, or metric system its all the same thing