Question

Which of the following metabolic pathways require(s) molecular oxygen \(\left(\mathrm{O}_{2}\right) ?\) a. aerobic respiration b. lactate fermentation c. alcoholic fermentation d. all of the above

Short answer

Only aerobic respiration requires molecular oxygen (\(\mathrm{O}_2\)).

Step-by-step solution

Understand the question

The question asks which metabolic pathways require molecular oxygen (\(\mathrm{O}_2\)). We need to examine each option to discover whether \(\mathrm{O}_2\) is a necessary component.

Review aerobic respiration

Aerobic respiration is a metabolic process that relies on \(\mathrm{O}_2\) to produce ATP by oxidizing glucose. Oxygen is the terminal electron acceptor in the electron transport chain, making it essential for the process.

Review lactate fermentation

Lactate fermentation is an anaerobic process that does not require \(\mathrm{O}_2\). It occurs in the absence of oxygen, where glucose is converted into lactate to regenerate NAD⁺ for glycolysis.

Review alcoholic fermentation

Similar to lactate fermentation, alcoholic fermentation is an anaerobic process and does not need \(\mathrm{O}_2\). In this pathway, glucose is converted to ethanol and carbon dioxide, also regenerating NAD⁺ for glycolysis.

Determine the correct answer

Given the review of the pathways, only aerobic respiration requires \(\mathrm{O}_2\), while both lactate fermentation and alcoholic fermentation occur in its absence.

Key concepts

Aerobic Respiration

Aerobic respiration is a crucial metabolic pathway that helps us transform glucose into energy. This process requires molecular oxygen (\(\mathrm{O}_2\)) to work effectively. Oxygen plays an essential role as the final electron acceptor in the electron transport chain, a series of reactions that occur in the mitochondria of cells.

• It starts with glycolysis, where glucose is broken down into pyruvate in the cytoplasm.
• Pyruvate then enters the mitochondria to undergo the Krebs cycle, generating carriers like NADH and FADH₂.
• The electron transport chain uses these carriers to create a proton gradient that drives ATP synthesis.
• Oxygen is vital here, as it combines with electrons and protons to form water, concluding the process.

This efficient energy production method is essential for high-energy demand tissues, like muscle and brain cells. Through aerobic respiration, cells gain more than 30 molecules of ATP from the complete oxidation of one glucose molecule, providing sustained energy for ongoing cellular functions.

Anaerobic Processes

Anaerobic processes are metabolic pathways that occur without the presence of oxygen. These processes kick in when oxygen levels are low or during intense activity, where energy is needed quickly.

• They primarily include both lactate fermentation and alcoholic fermentation.
• These processes focus on allowing cells to regenerate NAD⁺, which is crucial for glycolysis to continue producing ATP.

Although they are less efficient than aerobic respiration, anaerobic processes provide a rapid way for cells to keep generating small amounts of energy until oxygen becomes available again.
These pathways are vital in environments that lack oxygen altogether, such as certain bacteria living in oxygen-deprived conditions. In multicellular organisms, these routes help during short, intense periods of exertion. However, the trade-off is producing less ATP compared to aerobic systems, usually around 2 ATP molecules per glucose molecule.

Fermentation

Fermentation is an anaerobic process that allows cells to continue ATP production when oxygen is scarce. Two major types of fermentation are lactate fermentation and alcoholic fermentation.

• In lactate fermentation, pyruvate formed during glycolysis is reduced to lactate, particularly in muscle cells under strenuous activity.
• Alcoholic fermentation, occurring in yeast and some bacteria, converts pyruvate to ethanol and carbon dioxide.
• Both processes regenerate NAD⁺, allowing glycolysis to persist even in an oxygen-limited environment.

While providing only 2 ATP molecules per glucose, fermentation is a critical mechanism to sustain cellular function temporarily.
Fermentation not only plays a role in biological systems but also has numerous industrial applications. It is crucial in food and beverage production, such as in the making of bread, beer, and yogurt, where these specific by-products enhance product qualities.