Which one of the following components of the electron transport chain only accepts electrons, and does not donate them?

The component of the electron transport chain that only accepts electrons and does not donate them is NADH dehydrogenase (Complex I). In the electron transport chain, electrons are transferred between various components, but Complex I is specifically responsible for accepting electrons from NADH.

Here’s a brief overview of the electron transport chain components:

1. Complex I (NADH dehydrogenase): Accepts electrons from NADH and passes them to ubiquinone (Q). It does not donate electrons.
2. Complex II (Succinate dehydrogenase): Accepts electrons from succinate but also donates them to ubiquinone.
3. Complex III (Cytochrome bc1 complex): Accepts electrons from ubiquinol and donates them to cytochrome c.
4. Complex IV (Cytochrome c oxidase): Accepts electrons from cytochrome c and donates them to oxygen.

Thus, while several components accept and donate electrons, Complex I is unique in that it solely accepts electrons.