The DARK REACTION happen in the stroma of the chloroplasts. This is also known as the Calvin Cycle. Since these processes can only happen in the chloroplast (a chlorophyll filled plastid in green plants), photosynthesis can only happen in green plants
The point is that they do not require sunlight to complete their process.
Light reaction occurs in the grana of chloroplast. The chlorophyll absorbs the light energy. Hence the chlorophyll is called a photosystem or pigment system
