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With and without oxygen

The difference between respiration with oxygen and fermentation is not a small detail. If you use 30 ATP with oxygen and 2 without, oxygen gives fifteen times as much ATP per glucose. That is why we cannot run for long on lactic acid fermentation alone, and why yeast only makes a little alcohol before energy is scarce. Photosynthesis in plants replenishes both glucose and oxygen. Without it, cellular respiration in most ecosystems would stop. The two processes keep carbon cycling.

302=15\frac{30}{2} = 15times more ATP with oxygen

Symbols

3030ATP with oxygen
22ATP in fermentation

Example

With the numbers from the problems: 30/2=1530/2 = 15.

Oxygen gives 15 times as many ATP per glucose as fermentation.

Muscles make lactate, not ethanol. Ethanol is the product of yeast.
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Part of Biology 1: Photosynthesis and cellular respiration.