Anatomy of the Heart. Your heart is located under your ribcage in the center of your chest between your right and left lungs. Its muscular walls beat, or contract, pumping blood to all parts of your body. The size of your heart can vary depending on your age, size, and the condition of your heart.
In anaerobic respiration, NADH loses its electrons to other molecules in the process of fermentation for the purpose of regenerating the NAD+ needed to continue oxidizing organic molecules to produce ATP by substrate-level phosphorylation.
Aerobic respiration produces far more ATP than anaerobic respiration. Of the three steps in the cellular respiration process, glycolysis is assumed to be the oldest, having evolved early in the evolution of cells. The Krebs cycle and electron transport chain are thought to have evolved later.