In fermentation _ is reduced and _ is oxidized.
The correct answer and explanation is:
Correct Answer:
In fermentation, pyruvate is reduced and NADH is oxidized.
Explanation (300 words):
Fermentation is a metabolic process that allows cells to produce energy in the absence of oxygen. It is an anaerobic pathway that follows glycolysis, the breakdown of glucose into pyruvate. During glycolysis, glucose is converted into two molecules of pyruvate, and in the process, NAD⁺ is reduced to NADH as it accepts electrons.
However, for glycolysis to continue producing ATP, cells must regenerate NAD⁺. This is where fermentation becomes crucial. Since there is no oxygen to serve as the final electron acceptor (as in aerobic respiration), cells use fermentation to recycle NADH back to NAD⁺.
In this process:
- Pyruvate, the end product of glycolysis, is reduced to form products like lactic acid (in animals) or ethanol and CO₂ (in yeast).
- To reduce pyruvate, NADH donates its electrons, thereby being oxidized back to NAD⁺.
Thus, fermentation serves a dual purpose: it allows continued ATP production through glycolysis and maintains the redox balance in the cell by regenerating NAD⁺.
Examples:
- Lactic Acid Fermentation (in muscle cells and some bacteria):
Pyruvate + NADH → Lactic acid + NAD⁺ - Alcoholic Fermentation (in yeast):
Pyruvate → Acetaldehyde + CO₂
Acetaldehyde + NADH → Ethanol + NAD⁺
In both examples, NADH is oxidized to regenerate NAD⁺, and pyruvate or its derivative is reduced to maintain energy flow in the absence of oxygen.
In summary, fermentation ensures the continuous production of ATP under anaerobic conditions by reducing pyruvate and oxidizing NADH, keeping glycolysis functioning efficiently.