Since humans and other animals are capable of glycolysis, why do we need to breathe oxygen?
To understand why humans and other animals need to breathe oxygen despite their capability for glycolysis, we need to delve into the energy production processes in our cells. Glycolysis is the initial step in cellular respiration, which is a series of chemical reactions that occur in the presence of oxygen to produce energy in the form of ATP (adenosine triphosphate). It is an anaerobic (without oxygen) process that takes place in the cytoplasm of cells.
During glycolysis, glucose (a sugar molecule) is broken down into two molecules of pyruvate. This process generates a small amount of ATP. However, the energy production through glycolysis is relatively inefficient compared to the subsequent steps in cellular respiration that occur in the mitochondria, which require oxygen.
The next steps in cellular respiration, known as the citric acid cycle (or Krebs cycle) and the electron transport chain, can only occur in the presence of oxygen. These processes take place in the mitochondria of cells and are referred to as aerobic (requiring oxygen) respiration. They break down the pyruvate generated during glycolysis and extract significantly more ATP from each glucose molecule.
The electron transport chain, in particular, relies on oxygen as the final electron acceptor. Oxygen acts as a critical component by accepting electrons at the end of this chain, allowing for the efficient production of ATP. Without oxygen, the electron transport chain cannot function properly, leading to decreased ATP production.
In summary, while glycolysis can provide some energy through the breakdown of glucose without oxygen, it is a relatively inefficient process. Oxygen is essential for the subsequent stages of cellular respiration that occur in the mitochondria, where the majority of ATP is produced. Therefore, breathing oxygen is necessary to support the efficient and effective production of energy in animals, including humans.