Biology · Respiration in Plants · NEET
NCERT clearly states three. Pyruvic acid produced by glycolysis can go into (1) lactic acid fermentation, (2) alcoholic fermentation, or (3) aerobic respiration. The exact path a cell picks depends on the cell type and on whether oxygen is present.
Lactic acid fermentation and alcoholic fermentation are anaerobic — they happen when oxygen is absent or low. Only aerobic respiration needs an oxygen supply, because it fully oxidises glucose to CO2 and water through the Krebs cycle and the electron transport system.
In animal muscle, pyruvic acid is reduced to lactic acid by lactate dehydrogenase. In yeast, pyruvic acid decarboxylase and alcohol dehydrogenase convert pyruvic acid to CO2 and ethanol. In aerobic respiration, pyruvate dehydrogenase (the link reaction) turns pyruvate into acetyl CoA before the Krebs cycle.
Glycolysis is neither strictly aerobic nor anaerobic — it does not use oxygen and happens in the cytoplasm of all cells. It is only the fate of pyruvate after glycolysis that splits into anaerobic (fermentation) or aerobic (respiration) routes.
No. Acetyl CoA is formed only in the aerobic route, when pyruvate enters the mitochondrion and is oxidatively decarboxylated by pyruvate dehydrogenase. In fermentation, pyruvate becomes lactic acid or ethanol + CO2 in the cytoplasm — it never becomes acetyl CoA.
In both lactic acid and alcoholic fermentation, NADH + H+ is re-oxidised back to NAD+. This regenerated NAD+ lets glycolysis continue, since glycolysis needs NAD+. That is why cells can still make a little ATP without oxygen.
Match List I with List II: List I: A. Oxidative decarboxylation, B. Glycolysis, C. Oxidative phosphorylation, D. Tricarboxylic acid cycle List II: I. Citrate synthase, II. Pyruvate dehydrogenase, III. Electron transport system, IV. EMP pathway
Which of the following biomolecules is common to respiration-mediated breakdown of fats, carbohydrates and proteins?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Lactic acid fermentation, alcoholic fermentation, and aerobic respiration. Use the hook 'LAA' to recall all three.
Aerobic respiration. It fully oxidises glucose to CO2 and water and releases much more ATP. Both fermentation routes release less than seven per cent of the energy in glucose.
Fermentation (lactic acid and alcoholic) happens in the cytoplasm under anaerobic conditions. The aerobic fate moves pyruvate into the mitochondrion for the link reaction and Krebs cycle.
Lactate dehydrogenase, in animal muscle when oxygen is inadequate during hard exercise.
Alcoholic fermentation releases CO2 (along with ethanol). Lactic acid fermentation does not release CO2 — it only forms lactic acid.
