In a chloroplast, H+ pile up inside the thylakoids
- The idea
- Predict
- See it
- Why
- Check
The idea
“Like a mitochondrion, a chloroplast builds its H+ gradient between its two outer membranes.”
You just learned the mitochondrion, with H+ packed between its two membranes. A chloroplast has two envelope membranes too, so the same layout seems obvious.
The short version
The mistake: Like a mitochondrion, a chloroplast builds its H+ gradient between its two outer membranes.
What's actually true: H+ build up in the thylakoid lumen and flow out into the stroma, where ATP is made and the Calvin cycle runs.
- Match the parts by job. The thylakoid membrane holds the electron transport chain and ATP synthase, like the inner mitochondrial membrane.
- The lumen, the space inside each thylakoid, is like the intermembrane space. In light it fills with H+ and becomes more acidic than the stroma.
- The stroma, the fluid around the thylakoids, is like the matrix. ATP synthase releases ATP there, and the Calvin cycle uses it there.
On the exam: H+ pile into the thylakoid lumen. ATP comes out into the stroma. The envelope gap gets none.