The answer is glucose.

Quick Scoop

Cells need a constant supply of energy in the form of ATP, and this energy most commonly comes from breaking down the sugar glucose during cellular respiration. In many school-level biology questions like this, glucose is explicitly identified as the substance whose level must be maintained, alongside oxygen, to keep cells supplied with energy.

Why glucose?

  • Glucose is the primary fuel molecule that cells oxidize to make ATP, the main energy currency of the cell.
  • Other nutrients (fats, proteins) can be used, but they are usually converted into pathways centered around glucose breakdown, making glucose the key energy substrate in most organisms.

So, for the question “other than oxygen, the level of what substance needs to be maintained to give cells a constant supply of energy?” the substance is glucose.

TL;DR: Maintaining a steady level of glucose in the body ensures that cells can continuously produce ATP and stay alive and active.

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