d. the electron transport chain (and chemiosmosis) is the answer.
An electron transport chain is a series of protein complexes and other molecules that transfer electrons from an electron donor to an electron acceptor via a redox reaction and bind this electron transfer to the transfer of protons through the membrane.
The electron transport chain is a series of four protein complexes that combine redox reactions to produce an electrochemical gradient that leads to the formation of ATP in a complete system called oxidative phosphorylation. It occurs in mitochondria in both cellular respiration and photosynthesis.
The electron transport chain works by sending protons into the intermembrane space. This sets up a proton gradient that allows protons to be pumped through ATP synthase to produce ATP.
Learn more about chemiosmosis here:https://brainly.com/question/896642
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