The first pathway used to break glucose down and extract free energy is:

1. Glucose catabolism runs through several pathways in a fixed order. 2. The opening pathway acts on the intact six-carbon sugar. 3. Glycolysis is the first pathway used in the breakdown of glucose to extract free energy. 4. Used by nearly all organisms on earth today, it likely evolved as one of the first metabolic pathways. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 7 'Cellular Respiration', sections 7.1-7.7_