Question

Why is oxygen necessary for cellular respiration to occur?

Short answer

Oxygen is necessary for cellular respiration as it plays a crucial role in the electron transport chain, the primary source of ATP production in the cell. Serving as the final electron acceptor, oxygen enables the flow of electrons through protein complexes, allowing the formation of a proton gradient essential for ATP synthase to produce ATP molecules. Without oxygen, electron flow would halt, consequently disrupting ATP production and depriving the cell of the energy needed for vital biological processes.

Step-by-step solution

Introduction to cellular respiration

Cellular respiration is the process by which cells break down glucose and other organic molecules to produce energy in the form of Adenosine Triphosphate (ATP). The process consists of several stages, including glycolysis, the citric acid cycle (also known as the Krebs cycle), and the electron transport chain. Oxygen is a key component in the final stage, serving as the final electron acceptor.

Glycolysis

Glycolysis is the first stage of cellular respiration and takes place in the cell's cytoplasm. During glycolysis, one glucose molecule is broken down into two pyruvate molecules, generating 2 molecules of ATP and 2 molecules of NADH. This stage does not require oxygen, meaning it can occur under anaerobic conditions (without oxygen). However, the following stages (citric acid cycle and electron transport chain) need oxygen to proceed.

Citric acid cycle

The citric acid cycle (Krebs cycle) takes place in the mitochondria. During this cycle, the pyruvate produced in glycolysis is further broken down into carbon dioxide. The cycle generates 2 ATP molecules, 6 NADH molecules, and 2 FADH2 molecules. While the citric acid cycle does not directly use oxygen, it relies on a sufficient supply of oxygen to maintain the necessary reduced coenzymes NADH and FADH2.

Electron transport chain

The electron transport chain (ETC) is the final stage of cellular respiration and occurs in the inner mitochondrial membrane. In this stage, the NADH and FADH2 produced in the previous steps donate their electrons to a series of protein complexes. These electrons are being passed through the complexes, which pumps protons across the inner mitochondrial membrane, creating an electrochemical gradient. This gradient is ultimately used by the enzyme ATP synthase to produce the majority of ATP during cellular respiration (approximately 28-34 ATP molecules per glucose molecule). Oxygen plays a crucial role here, as it acts as the final electron acceptor and combines with the electrons and protons to form water. Without oxygen, the electron transport chain would be disrupted, and there would be no flow of electrons through the complexes. This, in turn, would prevent the generation of ATP through oxidative phosphorylation.

The necessity of oxygen

Oxygen is necessary for cellular respiration because it enables the smooth functioning of the electron transport chain, the primary source of ATP production in the cell. By acting as the final electron acceptor in the ETC, oxygen allows the electrons to flow through the various protein complexes. Without oxygen, this electron flow would stop, preventing the formation of the proton gradient necessary for ATP synthase to produce ATP molecules. This disruption in ATP production would deprive the cell of the energy it needs to carry out essential biological processes.