The utilisation of the energy rich ATP and NADPH molecules formed in the light dependent phase of photosynthesis for the production of  energy rich carbohydrates (sugars).

During the light dependent phase of photosynthesis, ATP and NADPH molecules accumulate in the stroma of the chlorophast. Although ATP is energy-rich it cannot be stored and it cannot be used for construction within the cell. It is therefore transformed into a carbohydrate (simple sugar) at first. These molecules also have energy-rich bonds, can be stored by cells and are the precursors for all other organic molecules produced by the cell.

Carbohydrates contain carbon (C), oxygen (O) and hydrogen (H) atoms. The cell obtains the oxygen and hydrogen atoms it needs for their construction from water, and the carbon and oxygen atoms from carbon dioxide present in air.  It is during the light independent phase of photosynthesis that the carbon dioxide absorbed by the plant is used.