Biology · Respiration in Plants · NEET
In NCERT, yes. NCERT treats fermentation (lactic acid or alcoholic) as the anaerobic breakdown of glucose in many prokaryotes and unicellular eukaryotes like yeast. Both mean glucose is broken down without oxygen and only incompletely. So for NEET, when the question says anaerobic respiration in the context of Chapter 12, it means fermentation.
Because anaerobic respiration is incomplete oxidation. Glucose is only split into pyruvate (glycolysis) and then converted to lactic acid or ethanol. The energy stays locked inside these end products. Aerobic respiration fully oxidises glucose to CO2 and water using the Krebs cycle and the electron transport system, so it can release much more energy. NCERT says less than seven per cent of the energy in glucose is released in fermentation.
Both are anaerobic. Alcoholic fermentation (by yeast) gives ethanol and CO2. Lactic acid fermentation (by some bacteria and in animal muscle) gives lactic acid and no CO2. Aerobic respiration produces neither; its end products are only CO2 and water. So alcohol and lactic acid are signs of the anaerobic path, not the aerobic one.
Yes. Glycolysis is common to both. Glucose is first broken into two pyruvate molecules in the cytoplasm, giving a net gain of 2 ATP. After this the paths split: with oxygen the pyruvate enters the mitochondria for aerobic respiration; without oxygen the pyruvate is turned into lactic acid or ethanol (fermentation).
Glycolysis happens in the cytoplasm for both. The extra fermentation reactions (pyruvate to lactic acid or ethanol) also stay in the cytoplasm, so anaerobic respiration is fully cytoplasmic. Aerobic respiration continues inside the mitochondria, where the Krebs cycle (matrix) and the electron transport system (inner membrane) occur. That is why mitochondria are called the power houses of the cell.
What amount of energy is released from glucose during lactic acid fermentation?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Aerobic respiration uses oxygen and fully oxidises glucose to CO2 and water, releasing about 36-38 ATP. Anaerobic respiration works without oxygen, only partly breaks glucose into lactic acid or ethanol, and gives a net of just 2 ATP.
Aerobic respiration gives about 36-38 ATP per glucose molecule. Anaerobic respiration (fermentation) gives a net of only 2 ATP per glucose molecule.
Aerobic respiration produces CO2 and water. Anaerobic respiration produces either lactic acid (lactic acid fermentation) or ethanol and CO2 (alcoholic fermentation).
Many prokaryotes and unicellular eukaryotes such as yeast do it, and human muscle cells switch to lactic acid fermentation during hard exercise when oxygen runs short.
Glycolysis itself does not need oxygen, so it happens in both types. It is the first common step; in anaerobic organisms it is the only respiratory process.
