Q16.In anaerobic conditions, yeast consumes more glucose than in the presence of aerobic environment. This phenomenon is known as-
(A) Hatch and Slack effect
(B) Emerson enhancement effect
(C) Warburg effect
(D) Pasteur effect
The correct answer is (D) Pasteur effect. Yeast consumes more glucose under anaerobic conditions due to lower ATP yield from fermentation compared to aerobic respiration.
Option Explanations
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(A) Hatch and Slack effect: This describes the C4 photosynthetic pathway in certain plants, where CO₂ fixation occurs via phosphoenolpyruvate carboxylase to minimize photorespiration. It has no relation to yeast glucose metabolism.
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(B) Emerson enhancement effect: This refers to enhanced photosynthetic rates in plants when both far-red and red light are provided together, overcoming the Emerson effect limitation. Unrelated to microbial respiration.
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(C) Warburg effect: Cancer cells exhibit high glycolysis and lactate production even aerobically, prioritizing rapid ATP and biomass for proliferation. In yeast, it links to glucose-induced respiration repression, but not specifically higher anaerobic consumption.
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(D) Pasteur effect: Yeast and facultative anaerobes consume more glucose anaerobically because glycolysis yields only 2 ATP per glucose, versus ~36 ATP aerobically via oxidative phosphorylation. Glucose uptake rises to compensate for inefficient energy production.
The Pasteur effect yeast anaerobic glucose consumption phenomenon explains why yeast uses more sugar without oxygen. Observed by Louis Pasteur in the 1860s, it highlights metabolic shifts in facultative anaerobes.
Biochemical Mechanism
Anaerobically, yeast ferments glucose to ethanol via glycolysis, netting 2 ATP per molecule. Aerobically, full oxidation through the Krebs cycle and electron transport yields ~36 ATP, slowing glycolysis via allosteric regulation (e.g., ATP inhibits phosphofructokinase). Without oxygen, yeast ramps up glucose uptake to match energy demands.
Comparison with Warburg Effect
Yeast models aspects of Warburg but inversely: glucose represses respiration.
Biological Significance
This effect optimizes industrial processes like brewing and bioethanol production by favoring fermentation. In exams, distinguish it from photosynthetic effects (A, B) for accurate scoring.
