Final answer:
Reducing agents or reductants, such as NADH and FADH2, donate electrons to the electron transport chain in the process of cellular respiration.
Step-by-step explanation:
The compounds that donate electrons to the electron transport chain are known as reducing agents or reductants. These are compounds capable of donating electrons because they are oxidized in the process.
In the context of cellular respiration, the main reducing agents that provide electrons to the electron transport chain are a class of compounds that includes Nicotinamide adenine dinucleotide (NADH) and Flavin adenine dinucleotide (FADH2), which are both derived from B vitamins and function as electron shuttles.
For example, NADH donates electrons that are ultimately used to reduce oxygen (O2) to water (H2O) in the electron transport chain.