Here's why:

* Glycolysis is the first stage of cellular respiration. It's a series of reactions that break down glucose (a simple sugar) into pyruvate.

* Glycolysis doesn't require oxygen. This makes it a fundamental process for all living things, regardless of whether they live in oxygen-rich or oxygen-poor environments.

* Glycolysis occurs in the cytoplasm of cells. This means it doesn't rely on specialized organelles like mitochondria, which are only present in eukaryotic cells.

While subsequent stages of respiration like the Krebs cycle and electron transport chain require oxygen, glycolysis provides a universal energy source for all life forms.