Question

Chloroplasts that are in the dark do not carry out photosynthesis. The light reactions do not occur to use light energy to make ATP and transfer electrons to NADPH. The Calvin Cycle is then not able to produce sugars from CO2. In an experiment, isolated chloroplasts were first made acidic by soaking them in a solution of pH 4. After the thylakoid space reached ph 4, the chloroplasts were transferred to a basic solution at pH 8. The chloroplasts then made ATP even though they were in the dark. Remember, pH is a read out of H+ concentration. Make sure your response answers the following questions:

a.under normal conditions, What happens to the Hydrogen gradient in the chloroplasts if they are in the dark?

Answer 1

Answer :)

Light causes the proton gradient because light induces the release of electrons. This causes the production of H+ ions that induce a proton-motive force. During this process, the pH around the transmembrane reaches 3.5. This pH drives more proton motive force until the light imposes on the leaf. Contrary, in the dark, there is no release of electron and pH around the thylakoid membrane becomes 7. This pH cannot drive proton motive force and hence there is no H+ gradient in the stromal.

That is why the role of pH around thylakoid membrane is so important.

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