Final answer:
There are two classes of electron carriers: those that carry electrons only and those that carry both H+ and electrons. Examples of electron carriers that carry electrons only include NAD+ and FAD. Examples of carriers that carry both H+ and electrons are NADH and FADH2.
Step-by-step explanation:
Electron carriers in living systems transport high-energy electrons between compounds in biochemical pathways. There are two classes of electron carriers: those that carry electrons only and those that carry both H+ and electrons. Examples of electron carriers that carry electrons only include nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD). On the other hand, examples of carriers that carry both H+ and electrons are NADH and FADH2.