Where does the light dependent reaction occur?
The light reaction occurs in the thylakoid membranes. Some of these are stacked in complexes called grana (singular granum). The blue arrows indicate thallakoids not associated with grana. The 'G' indicates grana. The light reaction generates ATP and NADPH required by the light independent reaction. The light reaction requires the structural integrity of the tylakoid membranes to generate ATP and NADPH.
Where does the light independent reaction occur?
The light independent reaction (the Calvin Cycle) occurs in the stroma labelled 'S'. The stroma is simply the space in the chloroplast not occupied by the thylakoids. The reactions that make up the Calvin cycle simply require the products of the light reaction, plus carbon dioxide all held together in a confined space to occur.
N = nucleus
MT = Mitachondria
C = Cytosol
M = Microbodies
St = Stach grains inside the chloroplast
Red arrow = double unit membrane of the chloroplast