Problem 13 - Biology

Question

A net profit of only 2 ATPs can be produced anaerobically from the ________ of one molecule of glucose, compared with a maximum of 38 ATPs produced in (a) fermentation; anaerobic respiration (b) aerobic respiration; fermentation (c) aerobic respiration; anaerobic respiration (d) dehydrogenation; decarboxylation (e) fermentation; aerobic respiration

Step-by-Step Solution

Answer

The answer is (e) fermentation; aerobic respiration.

Step 1: Understand Anaerobic ATP Production

Anaerobic processes like fermentation and anaerobic respiration result in a net gain of ATP. During fermentation, 2 ATP molecules are produced per glucose molecule, which arises during glycolysis, as no oxygen is involved.

Step 2: Compare with Aerobic ATP Production

In aerobic respiration, oxygen is present which allows the complete oxidation of glucose, leading to a much higher yield of ATP, commonly around 36 to 38 ATP per glucose molecule. This includes ATP from glycolysis, the Krebs cycle, and oxidative phosphorylation.

Step 3: Eliminate Invalid Options

Options that do not start with a process yielding 2 ATP are not suitable. Fermentation in option (e) produces 2 ATP anaerobically. Aerobic respiration in option (e) produces about 38 ATP, matching the description.

Step 4: Validate Correct Choice

Verify that (e) is correct. Fermentation provides 2 ATP, and aerobic respiration can yield up to 38 ATP, satisfying both conditions given in the question.

Key Concepts

Anaerobic Respiration

Anaerobic respiration occurs when oxygen is not available, and cells need to generate energy. Instead of the typical 36 to 38 ATP molecules produced in aerobic respiration, anaerobic processes are much less efficient. They yield only 2 ATP from the breakdown of one glucose molecule. This is because the process relies solely on glycolysis followed by pathways that regenerate NAD+, crucial for the continuation of glycolysis.
Glucose is partially oxidized, but as this process does not continue into the Krebs cycle or oxidative phosphorylation, much less energy is captured when compared to aerobic respiration.

• Occurs without oxygen
• Yields only 2 ATP per glucose molecule
• Processes include glycolysis and pathways like lactic acid or alcohol production

Each organism may use different molecules as final electron acceptors. For example, some bacteria use nitrate while others might use sulfate, rather than oxygen, to complete the process.

Aerobic Respiration

Aerobic respiration is a highly efficient energy-producing process that occurs in the presence of oxygen. This pathway enables cells to release significantly more energy than anaerobic processes. From one molecule of glucose, aerobic respiration can generate up to 38 ATP.
This impressive efficiency stems from the complete oxidation of glucose molecules. The process involves several stages, including glycolysis, the Krebs cycle, and oxidative phosphorylation.

• Requires oxygen
• Produces up to 38 ATP from one glucose molecule
• Consists of glycolysis, the Krebs cycle, and oxidative phosphorylation

Unlike anaerobic respiration, oxygen serves as the final electron acceptor, allowing for the maximum energy release from nutrient molecules.

Fermentation

Fermentation is a type of anaerobic respiration. It occurs when there is no oxygen available and cells need an alternative method to regenerate NAD+, allowing glycolysis to continue. Like anaerobic respiration, fermentation only produces a net gain of 2 ATP per glucose.
Two common types of fermentation are:

• Lactic acid fermentation: Converts pyruvate to lactic acid
• Alcoholic fermentation: Converts pyruvate to ethanol and carbon dioxide

Though it is energyinefficient compared to aerobic pathways, fermentation is crucial for energy production in cells lacking access to oxygen, such as muscle cells during intense exercise or yeast in brewing.

Glycolysis

Glycolysis is the initial step in both aerobic and anaerobic respiration, as well as in fermentation. This process occurs in the cytoplasm and does not require oxygen, making it vital for energy production across various organisms.
In glycolysis, one glucose molecule is broken down into two molecules of pyruvate, yielding 2 ATP and 2 NADH. Glycolysis serves as the springboard for further energy production, whether through anaerobic or aerobic pathways.

• Occurs in the cytoplasm
• Requires no oxygen
• Produces 2 ATP and 2 NADH per glucose molecule

Glycolysis provides a fundamental energy output, supporting cellular functions even under anaerobic conditions.