Correct Option
The correct option is 1, 2, 3 and 4.
Explanation
Cellular respiration is the process by which cells break down glucose to release energy. This process can occur in the presence of oxygen (aerobic respiration) or in its absence (anaerobic respiration or fermentation). The efficiency of energy release and the end products differ significantly between these two pathways.
Statement-wise Analysis
- Statement 1 is Correct: Fermentation involves the partial breakdown of glucose. Unlike aerobic respiration, which fully oxidizes glucose, fermentation converts glucose into simpler organic compounds like lactic acid or ethanol, leaving significant energy stored in the chemical bonds of these end products.
- Statement 2 is Correct: In fermentation, the net energy gain is low. For every molecule of glucose degraded to pyruvic acid (glycolysis), there is a net gain of only two molecules of ATP.
- Statement 3 is Correct: During respiration, NADH formed during glycolysis must be reoxidized to NAD+ to keep the cycle running. In fermentation, this reoxidation is a slow process. In contrast, during aerobic respiration, the reoxidation of NADH is vigorous and rapid due to the active Electron Transport Chain (ETC).
- Statement 4 is Correct: Aerobic respiration takes place in the mitochondria and leads to the complete oxidation of organic substances in the presence of oxygen. This releases carbon dioxide (CO2) and water (H2O) along with a large amount of energy (approximately 36-38 ATP molecules per glucose molecule).
Key Takeaway
Aerobic respiration is a high-energy process involving the complete oxidation of glucose to CO2 and H2O with vigorous NADH oxidation. Fermentation is a low-energy, partial breakdown process yielding only 2 ATP and involving slow NADH oxidation.