Question

Choose the equation of reaction that correctly represents anaerobic respiration in muscles:

• A. Glucose $\rightarrow$ Pyruvate $\xrightarrow{\text{Absence of O}_2}$ Ethanol + CO$_2$ + Energy
• B. Glucose $\xrightarrow{\text{O}_2}$ Pyruvate $\xrightarrow{\text{O}_2}$ Energy
• C. Glucose $\xrightarrow{\text{O}_2}$ Pyruvate $\xrightarrow{\text{Lack of oxygen}}$ Ethanol + Energy
• D. Glucose $\rightarrow$ Pyruvate $\xrightarrow{\text{Lack of oxygen}}$ Lactic acid + Energy

Hint:

Anaerobic respiration in muscles → Lactic acid formation. Yeast → Ethanol, Humans → Lactic acid.

Answer 1

The Correct Option is D

Anaerobic respiration in muscles occurs when there is a lack of oxygen. This process allows the muscles to continue generating energy even when oxygen is not sufficient, via glycolysis followed by additional chemical reactions that regenerate NAD⁺ from NADH, thereby permitting glycolysis to continue. In mammals, including humans, this anaerobic process results in the formation of lactic acid. Let's analyze the options given to identify the correct one.

• Option 1:
  Glucose → Pyruvate ⟶_{(Absence of O₂)} Ethanol + CO₂ + Energy: This reaction is typical of yeast during alcohol fermentation and is not applicable to muscle cells in humans. Therefore, this option is incorrect.
• Option 2:
  Glucose ⟶_(O₂) Pyruvate ⟶_(O₂) Energy: This represents aerobic respiration, involving the complete breakdown of glucose in the presence of oxygen to produce carbon dioxide, water, and energy. This is not characteristic of anaerobic respiration. Thus, this option is incorrect.
• Option 3:
  Glucose ⟶_(O₂) Pyruvate ⟶_{(Lack of oxygen)} Ethanol + Energy: Similar to Option 1, this reaction indicates alcohol fermentation, not relevant to muscle cells in humans. Therefore, this option is also incorrect.
• Option 4:
  Glucose → Pyruvate ⟶_{(Lack of oxygen)} Lactic acid + Energy: In conditions where oxygen is scarce, muscles temporarily convert pyruvate into lactic acid, rather than acetyl-CoA, to continue producing ATP through anaerobic glycolysis. This is the correct representation of anaerobic respiration in muscle tissues.

Conclusion: The correct answer is "Glucose → Pyruvate ⟶_{(Lack of oxygen)} Lactic acid + Energy", as it accurately represents the process of anaerobic respiration in muscle cells, where pyruvate is converted to lactic acid to produce energy in the absence of oxygen.