In a lit chloroplast the lumen has a pH of 5 and the stroma has a pH of 8…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In a lit chloroplast the lumen has a pH of and the stroma has a pH of . (a) What is the difference in pH? (b) How many times higher is the proton concentration in the lumen than in the stroma? (c) Which side is more acid?
Need a reminder? The key ideaShow
Chemiosmosis: a membrane, a proton pump, a proton gradient and ATP synthase. Protons collect in the lumen (water splitting, the carrier that moves protons across, and NADP reductase using stroma protons). ATP synthase: CF0 is a channel in the membrane, CF1 sticks into the stroma and makes ATP. Each pH unit is a factor of ten in the proton concentration. The ATP and NADPH go to the stroma.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The difference. pH units.
Step 2. The ratio. Each pH unit is a factor of , so times.
Step 3. The acid side. The lumen has the lower pH, so it is the more acid side.
Check. A gradient of times is large, which is why the flow back through CF0 can drive the making of ATP.
Answer: (a) ; (b) times; (c) the lumen.
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