Problem 23 - Objective Biology for NEET

Question

\(\mathrm{O}_{2}\) acts as (a) Terminal hydrogen acceptor (b) Terminal electron acceptor (c) Both (a) and (b) (d) None of these

Step-by-Step Solution

Answer

(b) Terminal electron acceptor

Step 1: Recall the Role of Oxygen in Cellular Respiration

In cellular respiration, especially during the final stage known as oxidative phosphorylation, Oxygen acts as the terminal electron acceptor. It accepts electrons that have passed through the electron transport chain. Electrons transfer their energy to Oxygen in a series of steps, and then Oxygen finally becomes reduced when it also accepts protons (H+) from the surrounding medium, forming water (H2O).

Step 2: Analyze answer options

Given this understanding of the function of Oxygen in cellular respiration, let's consider the answer choices: \n (a) says that Oxygen acts as a terminal hydrogen acceptor: This is not accurate. While Oxygen does end up forming water (\(H_2O\)), which includes hydrogen, it is not accurate to say that Oxygen primarily accepts hydrogen.\n(b) says that Oxygen acts as a terminal electron acceptor: This is accurate, as explained previously, Oxygen is the final recipient of electrons in the electron transport chain.\n(c) says both (a) and (b) which includes the incorrect statement about Oxygen primarily accepting hydrogen.\n(d) says none of the above which is not the case as (b) is true.

Step 3: Select the Correct Answer

Based on the provided analysis, the correct answer is (b) - Oxygen acts as a terminal electron acceptor.

Key Concepts

Oxidative Phosphorylation

Oxidative phosphorylation is the final stage of cellular respiration, a critical process used by cells to generate energy. During this stage, energy stored in the NADH and FADH2 molecules, which are produced earlier in glycolysis and the citric acid cycle, is used to create ATP, the cell's energy currency. This process takes place in the mitochondria, often referred to as the powerhouse of the cell.

• Oxidative phosphorylation consists of two main parts: the electron transport chain and chemiosmosis.
• Electrons released from NADH and FADH2 flow through protein complexes located in the inner mitochondrial membrane.
• This electron flow powers the pumping of protons from the mitochondrial matrix into the intermembrane space, creating a gradient.

The proton gradient generated provides the necessary energy for ATP synthase to synthesize ATP from ADP and inorganic phosphate. Without oxidative phosphorylation, cells would not efficiently produce ATP, which is essential for various cellular functions.

Electron Transport Chain

The electron transport chain is a series of protein complexes and small molecules embedded in the inner membrane of the mitochondria. This chain is a crucial component of cellular respiration because it facilitates the transfer of electrons from donors to acceptors such as oxygen. Here's how it works:

• Electrons are donated by NADH and FADH2, which are generated in earlier stages of cellular respiration.
• The electrons pass through complexes I, II, III, and IV within the mitochondrial membrane.
• As electrons travel through these complexes, energy is released, which is used to pump protons into the intermembrane space of the mitochondria.

The building of the proton gradient across the membrane is vital as it leads to ATP production. The energy from the gradient is harnessed by ATP synthase to phosphorylate ADP into ATP. Without the electron transport chain, oxidative phosphorylation wouldn't occur, and cells would not have a sustained supply of energy.

Terminal Electron Acceptor

In cellular respiration, the terminal electron acceptor is one of the key players in the electron transport chain. Oxygen serves as the final electron acceptor in the chain. This role is crucial for several reasons:

• Oxygen accepts electrons after they have passed through all the complexes of the electron transport chain.
• By accepting the electrons, oxygen helps to maintain the flow of electrons throughout the chain.
• When oxygen receives electrons, it combines with protons to form water. This is crucial since it prevents the backup of electrons in the chain.

Without oxygen acting as the terminal electron acceptor, the electron transport chain would cease to function, halting ATP production. This highlights oxygen's vital role in cellular energy production and underscores why it is essential for life.