My professor said that light reactions and dark reactions happen at the thylakoid. He did not choose the answer that "both reactions happen at chloroplast".

Isn't the thylakoid a part of the chloroplast?


1 Answer 1


The light dependent reactions involve an electron transport chain with enzymes embedded in the thylakoid membrane. NADPH and ATP are generated in the stroma and water is oxidized in the thylakoid lumen.

I'm not sure if it's correct to say that the light independent reactions occur "at the thylakoid" since, in plants, they could really occur anywhere in the stroma (not necessarily "at" the thylakoid, and certainly not within it). It's possible that the enzymes involved in the light independent reactions are somehow localised at the the stromal side of the thylakoid membrane for efficient use of substrates, but I have no idea if that is actually the case and I don't have time to review any literature.

In plants, all of these processes occur in the chloroplast. However, photosynthetic bacteria don't have chloroplasts so you can't categorically say that the photosynthetic reactions occur only within chloroplasts. Cyanobacteria do have thylakoids where the light dependent reactions occur.


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