Question

In the third stage of aerobic respiration, _____ is the final acceptor of electrons. a. water c. oxygen \(\left(\mathrm{O}_{2}\right)\) b. hydrogen d. NADH

Short answer

Oxygen (eta O_2)eta) is the final electron acceptor.

Step-by-step solution

Understanding the Context

In the process of aerobic respiration, electrons are transferred through a series of protein complexes known as the electron transport chain. The final step of this process involves the transfer of electrons to an ultimate electron acceptor, which completes the process of energy production.

Identifying Potential Final Electron Acceptors

Consider the given options: water (a), oxygen (c), hydrogen (b), and NADH (d). Each of these components serves a different role in cellular respiration. Determine which one acts as an electron acceptor at the end of the electron transport chain.

Analyzing Each Option

Option (a), water, is the product formed when the final electron acceptor reacts with protons and electrons. Option (b), hydrogen, acts as an electron carrier earlier in the process but not as the final acceptor. Option (d), NADH, is an electron carrier that donates electrons to the chain, not an acceptor. Option (c), oxygen, is well-known for acting as the final electron acceptor in the electron transport chain.

Concluding the Final Electron Acceptor

Oxygen (eta O_2)eta) serves as the final electron acceptor by combining with electrons and protons to form water, which completes the process of aerobic respiration.

Key concepts

Electron Transport Chain

The electron transport chain is an essential phase of aerobic respiration that occurs within the inner membrane of the mitochondria. This process involves a series of protein complexes that transfer electrons from electron carriers like NADH and FADH₂ to oxygen. These proteins include complexes I through IV, each playing a role in moving electrons step by step down the chain.
Electrons are transferred due to the energy differences between the carriers, allowing energy to be harnessed efficiently. As electrons move down this chain, protons are pumped from the mitochondrial matrix into the intermembrane space, creating a proton gradient. This gradient, also known as a proton-motive force, is crucial for producing ATP, the energy currency of the cell. The movement of protons back into the mitochondria through ATP synthase drives the synthesis of ATP from ADP and inorganic phosphate.
In essence, the electron transport chain is vital for energy production because it facilitates the efficient transfer and utilization of electrons, ultimately enabling cells to generate energy in the form of ATP.

Electron Acceptor

In the electron transport chain, each complex passes electrons to the next, ultimately reaching a final electron acceptor. Oxygen plays the critical role of being this final electron acceptor in aerobic respiration. Without an electron acceptor to complete the process, the electrons would build up, halting the chain and the production of ATP.
Oxygen combines with electrons and protons at the end of the electron transport chain to form water. This reaction not only completes the electron flow across the chain but also helps to maintain the proton gradient necessary for ATP production. The efficiency of oxygen as an electron acceptor is unmatched in the cell due to its high electronegativity, which means it has a strong tendency to attract electrons. This property helps drive the electron transport chain vigorously towards ATP synthesis. Hence, oxygen is indispensable for aerobic organisms because it enables the rapid and efficient generation of energy.

Energy Production

The process of energy production in the electron transport chain is vital for cell survival and function. By converting the energy stored in NADH and FADH₂ into ATP, cells are equipped with the energy needed to perform various functions. The central aspect of energy production via aerobic respiration is the conversion of these electron carriers’ energy into usable ATP. Through the movement of electrons and the resulting proton gradient, ATP synthase, a specialized enzyme, facilitates the conversion of ADP to ATP. This is analogous to water running through a turbine in a hydroelectric dam, where the flow drives the mechanical action leading to energy production. Thus, the electron transport chain is at the heart of aerobic respiration, providing a highly efficient mechanism for ATP synthesis. Without it, organisms would be unable to generate sufficient amounts of ATP from glucose metabolism, underscoring its critical role in cellular energy dynamics.