AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
(B) Yeast during fermentation
Yeast converts pyruvate into ethanol and carbon dioxide in the absence of oxygen. This is called anaerobic respiration (fermentation).
The passage from Section 5.3 explicitly states: "the pyruvate may be converted into ethanol and carbon dioxide. This process takes place in yeast during fermentation… it is called anaerobic respiration." Human muscle cells produce lactic acid (not ethanol) under anaerobic conditions — a common trap in this question. Fish in oxygenated water and leaves during the day perform aerobic respiration. Examiners often use this question to test whether students can distinguish between the two anaerobic pathways (yeast → ethanol + CO₂ vs. muscle → lactic acid).