Question

Fermentation is a process where

• A. Glucose is converted into pyruvate in the presence of oxygen
• B. Glucose is converted into pyruvate in the absence of oxygen
• C. Glucose is converted into lactate and / or alcohol in the absence of oxygen
• D. Glucose is converted into lactate and / or alcohol in the presence of oxygen

Hint:

• Fermentation is an anaerobic process (no oxygen required).
• It starts with glycolysis (glucose \(\rightarrow\) pyruvate).
• The main purpose of the steps after glycolysis in fermentation is to regenerate NAD\(^+\) so glycolysis can continue.
• Common end products: Lactic acid (lactic acid fermentation), Ethanol and CO\(_2\) (alcoholic fermentation).

Answer 1

The Correct Option is C

Fermentation is an anaerobic metabolic process (occurs in the absence of oxygen) that follows glycolysis. In fermentation, organic molecules (like pyruvate, the end product of glycolysis) are converted into other organic end products, such as lactic acid or ethanol and carbon dioxide. The primary purpose of fermentation in this context is to regenerate NAD\(^+\) from NADH, which allows glycolysis to continue producing a small amount of ATP.

• Glycolysis (common first step): Glucose \(\rightarrow\) Pyruvate + ATP + NADH. This step itself does not require oxygen.
• Fermentation (anaerobic): Pyruvate (or its derivatives) is then processed further without oxygen to regenerate NAD\(^+\).
  • Lactic acid fermentation: Pyruvate \(\rightarrow\) Lactic acid (e.g., in muscle cells, some bacteria).
  • Alcoholic fermentation: Pyruvate \(\rightarrow\) Acetaldehyde \(\rightarrow\) Ethanol + CO\(_2\) (e.g., in yeast).

Let's analyze the options: (a) "Glucose is converted into pyruvate in the presence of oxygen": Glycolysis (glucose to pyruvate) can occur with or without oxygen. If oxygen is present, pyruvate usually enters aerobic respiration. This is not fermentation. (b) "Glucose is converted into pyruvate in the absence of oxygen": This describes glycolysis under anaerobic conditions, which is the *prelude* to fermentation, but not fermentation itself (which processes the pyruvate). (c) "Glucose is converted into lactate and / or alcohol in the absence of oxygen": This correctly describes the overall process including glycolysis followed by the fermentation steps that produce end products like lactate or alcohol, all occurring anaerobically. (d) "Glucose is converted into lactate and / or alcohol in the presence of oxygen": Fermentation is an anaerobic process. If oxygen is present, cells typically perform aerobic respiration for much higher ATP yield. Therefore, option (c) best describes fermentation. \[ \boxed{\text{Glucose is converted into lactate and / or alcohol in the absence of oxygen}} \]