By number one what two molecules enter the krebs cycle only to carry away high energy electrons

The two molecules that enters the Krebs cycle that carry out high energy electron are NADH and FADH2.

Explanation:

Both NADH and FADH2 are reducing agent.They are the reducing form of NAD+ and FAD.

              NAD+ and FAD act as coenzymes and enter into krebs cycle and  get reduced into NADH and FADH2 by taking high energy electrons.

           Both NADH and FADH2 then enters the Electron Transport Chain to be converted into their original form that is NAD+ and FAD.

when it is at an intermediate population density