A hydrogen carrier is an organic macromolecule that transports atoms of hydrogen from one place to another inside a cell or from cell to cell for use in various metabolical processes. An example is NADPH in photosynthesis also called NAD along with it FAD is also one of the hydrogen carriers.The main role of these is to transport hydrogen atom to electron transport chain which will change ADP to ATP by adding one phosphate.
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Hydrogen carrier Wikipedia(Text) CC BY-SA