part 1: when photosynthesis is fully operational under conditions of intense light, the ph of the thylakoid lumen may be as much as three full ph units lower than the ph of the stroma of the chloroplast. that means that there are [ select ] protons in the thylakoid lumen compared to the stroma and a very large electrochemical gradient. part 2: you just discovered that the outer membrane of the mitochondria is permeable to small molecules so even ions can pass through. the ph of the intermembrane space of the mitochondria is 7.4 which is the same as the ph of the cytoplasmic fluid (cytosol). you are excited and ready to announce that this is conclusive evidence that the chemiosmotic theory is wrong!!!!! then you measure that the ph of the matrix is close to 8. the electrochemical gradient is much less in the mitochondria compared to the chloroplast but there is still a higher concentration of protons in the intermembrane space compared to the matrix because [ select ]