AAT Bioquest

What are the stages of photosynthesis?

Posted August 25, 2022


Photosynthesis takes place over multiple steps, which are grouped under two main stages – Light Phase or Light Dependent Reactions, which occur in Stage One and Dark Phase or Light Independent Reactions, which occur in Stage Two. 

Stage One: Light Phase or Light-Dependent Reactions

Sunlight is a key requirement for this stage of photosynthesis. 

During the light-dependent stage, chlorophyll absorbs energy from sunlight and converts it into the form of energy molecules, adenosine triphosphate (ATP) and electron carrier molecules nicotinamide adenine dinucleotide phosphate (NADPH)

Stage one takes place in the thylakoid membranes in the granum, within the chloroplast. 

An oxygen by-product is produced during this light phase. The chemical bonds in ATP and NADPH store energy, which is used during the next stage. 


Stage Two: Dark Phase or Light-Independent Reactions

The dark phase does not require sunlight and uses the ATP and NADPH molecules generated during the light phase. It is also known as the Calvin cycle or C3 cycle. 

During this light-independent phase, ATP and NADPH are used to assemble carbohydrate molecules from carbon dioxide and water. One molecule of glucose or sugar is produced from six molecules of carbon dioxide. These sugars will be used by the plant in order to grow and live. This stage occurs in the stroma.

Additional resources

Efficiency of photochemical stages of photosynthesis in purple bacteria (a critical survey)