Question

What amount of energy is released from glucose during lactic acid fermentation?

• A. Approximately 15%
• B. More than 18%
• C. About 10%
• D. Less than 7%

Answer 1

The Correct Option is D

During lactic acid fermentation, the energy released from glucose is significantly lower compared to aerobic respiration. The process involves the breakdown of one molecule of glucose into two molecules of lactic acid, with a net gain of only 2 ATP (adenosine triphosphate) molecules per glucose molecule.

To understand why the energy yield is less than 7%, consider the energy content of glucose in different pathways:

• In aerobic respiration, one glucose molecule can produce up to about 36-38 ATP molecules. Each ATP molecule is an energy currency for cells, correlating with a conservation of energy.
• In contrast, lactic acid fermentation produces only 2 ATP molecules per glucose molecule, as it does not proceed through the complete oxidation of glucose.

Energy Release Calculation:

Glucose contains approximately 720 kcal/mol; in aerobic respiration, these convert to ~38 ATP, so each ATP is worth about 720/38 ≈ 19 kcal.

During fermentation:

• Each glucose yields 2 ATP, releasing 2 x 19 = 38 kcal/mol of energy.
• This is approximately (38/720) x 100 = 5.28% of the total energy content of glucose.

Therefore, the energy release from glucose during lactic acid fermentation is less than 7%, aligning with the correct answer: Less than 7%.

Answer 2

Explanation: Lactic acid Fermentation releases less than 7% of the energy found in glucose, and not all of it is stored as ATP.

• The process of producing ATP in the absence of oxygen, through glycolysis alone is called fermentation.
• Glycolysis breaks glucose molecules into 2 molecules of pyruvate resulting in 2 ATP and 2 NADH molecules.
• Lactic acid fermentation is carried out by Lactobacillus.
• This type of fermentation involves anaerobic respiration.

In Lactic acid fermentation, 3-carbon pyruvate is converted into 3-carbon lactic acid (C3H6O3) and produces NAD+, allowing glycolysis to continue to make ATP in low-oxygen conditions. As there is a limited supply of NAD+ available in a given cell, the electron acceptor is regenerated to allow ATP production to continue. To do this, NADH regenerates NAD+ by donating its excess electrons to the pyruvate molecules. Pyruvate is reduced to produce lactic acid. Pyruvate is converted to lactic acid through lactic acid fermentation, which also produces NAD+ from NADH.

So, the correct option is (D): Less than 7%