Final answer:
NADH plays a crucial role as an electron carrier in the Krebs Cycle and as a substrate for NADH dehydrogenase in the respiratory chain/chemiosmosis.
Step-by-step explanation:
In the Krebs Cycle, NADH serves as an electron carrier, which means it helps transport electrons during the redox reactions of the cycle. These electrons are eventually used to generate ATP in the electron transport chain and chemiosmosis.
In the respiratory chain/chemiosmosis, NADH is a substrate for NADH dehydrogenase, an enzyme that catalyzes the transfer of electrons from NADH to the electron transport chain. This is the first step in the chain and is essential for the flow of electrons and eventual ATP production.