Question

The final acceptor of electrons in the electron transport chain is (A) hydrogen (B) water (C) oxygen (D) NADH (E) \(\mathrm{FADH}_{2}\)

Short answer

(C) oxygen

Step-by-step solution

Understand the electron transport chain

The electron transport chain is the last component of aerobic respiration and is the only part of glucose metabolism that uses atmospheric oxygen. Electrons are transferred from electron carriers to oxygen molecule.

Identify the final electron acceptor

In the process, energy is used to pump hydrogen ions across the inner mitochondrial membrane, storing energy as potential energy. At the end of the chain, the final electron acceptor is an oxygen molecule, which is reduced to water by accepting the electrons and proton.

Match the answer

From the given options, this points us towards (C) oxygen. Therefore, oxygen is the final acceptor of electrons in the electron transport chain.

Key concepts

Final Electron Acceptor

In the electron transport chain, the journey of electrons ends with the final electron acceptor. This is a key part of how cells produce energy during aerobic respiration. Electrons are transferred along a series of proteins embedded in the inner mitochondrial membrane. Their movement helps pump hydrogen ions, creating an energy gradient.
At the end of this chain, the ultimate role is played by oxygen. Oxygen is critical here as it accepts electrons and combines with hydrogen ions. This process forms water, completing the electron transport chain. Without this final electron acceptor, the chain would stall, and cells wouldn't produce ATP efficiently. This is why oxygen is vital in many forms of life.

Aerobic Respiration

Aerobic respiration is a process that uses oxygen to convert glucose into usable energy in the form of ATP. It occurs in the mitochondria of cells and involves several steps:

• Glycolysis, where glucose is broken down in the cell's cytoplasm.
• The Citric Acid Cycle, releasing more electrons.
• The Electron Transport Chain, where most ATP is produced.

During aerobic respiration, oxygen acts as the final electron acceptor at the end of the electron transport chain. This step is crucial because it allows for the complete oxidation of glucose, resulting in more energy produced compared to anaerobic pathways. Without oxygen, cells would rely on less efficient methods to produce energy.

Oxygen Reduction

Oxygen reduction refers to the process where oxygen molecules accept electrons during aerobic respiration. In the electron transport chain, electrons carried by NADH and \mathrm{FADH}_2 pass through proteins and finally reach oxygen. This interaction reduces oxygen to water, specifically:

• The oxygen molecule accepts a pair of electrons.
• Hydrogen ions also bind to the oxygen, forming water (H\(_2\)O).

This reaction is essential because it helps maintain a flow of electrons through the chain, allowing for continuous ATP production. Oxygen reduction is a redox reaction—a simultaneous reduction (gain of electrons) of oxygen and oxidation (loss of electrons) of another substance.

Glucose Metabolism

Glucose metabolism is the process by which cells break down glucose to release energy. It's a complex sequence starting with glycolysis in the cell's cytoplasm. Here, glucose is divided into two molecules of pyruvate.
Next, in the mitochondria, these pyruvate molecules enter the Citric Acid Cycle, producing high-energy electron carriers, NADH and FADH\(_2\). These carriers shuttle electrons to the electron transport chain.
In glucose metabolism, oxygen is crucial at the very last step, where it acts as the final electron acceptor. The entire process is efficient, producing up to 36-38 ATP molecules from one glucose molecule, showcasing why glucose and its metabolism are vital for cell survival and energy needs.