Which metabolic processes can occur without a net influx of energy from some other process?

The only reaction here that can be done without a net influx of energy is C6H12O6 + 6 O2 > 6 CO2 + 6 H20. This is the process of converting oxygen and sugar (glucose) to carbon dioxide and water. It’s cellular respiration. The sugar and oxygen are provided by eating and breathing, respectively.

Since the glucose breaks down to give its hydrogens to the oxygen, it really doesn’t need a lot of energy to begin, and it doesn’t need a lot of energy to keep going. It simply needs a small spark, so to speak, and then it can keep going until it’s done. Feeding it is not much of an issue, and can be fed by the process of glycolysis, which takes place right before this.