Problem 6 - Campbell Biology Concepts & Connections

Question

Which of the following is a distinction between cellular respiration and fermentation? a. NADH is oxidized by passing electrons to the electron transport chain in respiration only. b. Only respiration oxidizes glucose. c. Substrate-level phosphorylation is unique to fermentation; cellular respiration uses oxidative phosphorylation. d. Fermentation is the metabolic pathway found in prokaryotes; cellular respiration is unique to eukaryotes.

Step-by-Step Solution

Answer

Option A is the distinction: NADH is oxidized by passing electrons to the electron transport chain in respiration only.

Step 1: Understand the Question

Identify that the question is testing knowledge of the differences between cellular respiration and fermentation. Pay attention to each option provided.

Step 2: Analyze Option A

Option A discusses the oxidation of NADH. Recall that in cellular respiration, NADH is oxidized by passing electrons to the electron transport chain, which is not a feature of fermentation.

Step 3: Analyze Option B

Option B asserts that only respiration oxidizes glucose. Note that both respiration and fermentation involve the oxidation of glucose, though by different mechanisms.

Step 4: Analyze Option C

Option C claims that substrate-level phosphorylation is unique to fermentation and that cellular respiration uses only oxidative phosphorylation. However, cellular respiration also includes substrate-level phosphorylation during glycolysis and the citric acid cycle.

Step 5: Analyze Option D

Option D suggests that fermentation is exclusive to prokaryotes while cellular respiration is unique to eukaryotes. Remember that both prokaryotes and eukaryotes can perform fermentation and cellular respiration.

Step 6: Identify the Correct Answer

From the analysis, option A is the only correct distinction: NADH is oxidized by passing electrons to the electron transport chain in respiration only.

Key Concepts

NADH oxidation

NADH oxidation is a crucial part of cellular respiration. In this process, the molecule NADH donates its high-energy electrons to the electron transport chain (ETC). This occurs during the oxidative phosphorylation stage of cellular respiration.

NADH is produced during glycolysis and the citric acid cycle. It holds onto the high-energy electrons from glucose.

When NADH reaches the ETC, it releases these electrons. This process regenerates NAD+, which can then be used again in glycolysis and the citric acid cycle.

In fermentation, NADH is also oxidized, but it does not involve the electron transport chain. Instead, the electrons from NADH are directly transferred to an organic molecule, regenerating NAD+ without generating as much ATP.

Electron transport chain

The electron transport chain (ETC) is the final stage of cellular respiration. Located in the inner mitochondrial membrane in eukaryotes, it consists of a series of protein complexes.

Here's how it works:

• NADH and FADH2 donate electrons to the ETC
• These electrons pass through multiple protein complexes
• As electrons move, protons (H+) are pumped into the intermembrane space
• A proton gradient is created, generating a potential energy

The final electron acceptor in the ETC is oxygen, forming water. The energy stored in the proton gradient is then used to make ATP from ADP through a process known as ATP synthesis mechanized by ATP synthase.

Substrate-level phosphorylation

Substrate-level phosphorylation occurs during glycolysis and the citric acid cycle.

In this process, a phosphate group is directly transferred from a high-energy substrate to ADP, forming ATP.

This contrasts with oxidative phosphorylation, where ATP is produced indirectly via the ETC and proton gradient.

Despite these differences, both methods are crucial for ATP production. During glycolysis, substrate-level phosphorylation produces a small amount of ATP directly.

In fermentation, substrate-level phosphorylation is the sole method of ATP production, as it doesn't use an electron transport chain.

Oxidative phosphorylation

Oxidative phosphorylation is a process in cellular respiration where ATP is generated from the energy released by electrons as they are transferred to oxygen in the electron transport chain.

Here's a brief overview:

• NADH and FADH2, produced during glycolysis and the citric acid cycle, donate electrons to the ETC
• Electrons move through the complexes of the ETC
• Protons are pumped across the inner mitochondrial membrane
• A gradient is formed
• Protons flow back into the mitochondrial matrix through ATP synthase
• This drives the production of ATP from ADP

This process is highly efficient and generates most of the ATP produced in cellular respiration.

Prokaryotes vs Eukaryotes

Both prokaryotes and eukaryotes can perform fermentation and cellular respiration, but there are key differences in how these processes occur in each type of cell.

In prokaryotes:

• Cellular respiration occurs in the cytoplasm and on the plasma membrane, as they lack mitochondria
• They can perform both aerobic and anaerobic respiration

In eukaryotes:

• Cellular respiration primarily takes place in the mitochondria
• They rely mainly on aerobic respiration
• However, some eukaryotic cells can perform fermentation under anaerobic conditions

Despite these differences, the basic principles of ATP production through oxidation of glucose are similar in both types of cells.