alleryStart learning →In which direction do hydrogen ions diffuse when adenosine triphosphate is made in the chloroplast?
AFrom the stroma into the cytoplasm
BFrom the lumen into the outer envelope
CFrom the lumen into the stroma
DFrom the stroma into the lumen
Answer & Solution
Correct answer: C. From the lumen into the stroma
1. The buildup of hydrogen ions inside the thylakoid lumen creates a concentration gradient.
2. Hydrogen ions are at high concentration in the lumen and low concentration in the stroma.
3. Their passive diffusion from lumen to stroma is harnessed to create adenosine triphosphate.
4. The ions build up energy both from diffusion and from repelling one another, since they share the same charge.
5. Reversing the direction would describe the pumping step rather than the release step.
6. The same arrangement works in the electron transport chain of cellular respiration.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 8 "Photosynthesis", section 8.2 The Light-Dependent Reactions of Photosynthesis_
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