Here's why:

* Mitochondria are the powerhouses of the cell, primarily responsible for aerobic respiration (using oxygen to produce energy).

* Glycolysis is the first stage of cellular respiration, and it's an anaerobic process (doesn't require oxygen). It breaks down glucose into pyruvate.

Think of it like this:

* Glycolysis is the first step in a long journey – it happens outside the city (cytoplasm).

* Mitochondria are like the power plant in the city (the cell). The pyruvate from glycolysis then enters the mitochondria for the next steps of cellular respiration.