Final answer:
Yeast can survive anaerobic respiration by fermenting sugars into alcohol and carbon dioxide, producing energy even without oxygen. Humans, being obligate aerobes, cannot live for long in anaerobic conditions as our cells rely on oxygen to efficiently produce ATP, with lactic acid fermentation as a temporary and less efficient alternative.
Step-by-step explanation:
Why Can Yeast Survive Anaerobic Respiration but Humans Cannot?
Humans require aerobic respiration to survive, which involves using oxygen to convert glucose into ATP (adenosine triphosphate), the energy currency of cells. However, some organisms, such as yeast, can survive on anaerobic respiration, occurring without oxygen, also known as fermentation. These organisms, including some plants, fungi, and bacteria, thrive in various conditions and have evolved to utilize whatever resources are available. Yeast, for instance, is a facultative anaerobe, meaning it prefers oxygen but can adapt to its absence by fermenting sugars into alcohol and carbon dioxide.
In contrast, humans are obligate aerobes; we cannot sustain life for long without oxygen, as our cells require aerobic respiration to efficiently produce ATP. When oxygen is scarce, human cells can temporarily resort to lactic acid fermentation, which is much less efficient and not viable for our long-term survival. In anaerobic conditions, fermentation in human muscle cells leads to the accumulation of lactate and the rapid onset of fatigue.
Initially, all life on Earth had to survive without oxygen as it was not present in the early atmosphere. Over billions of years, life forms diverged, and metabolic pathways evolved. The shared ancestry of these pathways suggests that organisms like yeast retained the ability to perform anaerobic respiration, while humans, evolving in an oxygen-rich environment, became specialized for aerobic metabolism. Consequently, yeast can thrive anaerobically by leveraging fermentation to generate energy, even though it yields far less ATP compared to aerobic respiration. But humans, with high energy demands and specialized cells, cannot survive long-term on anaerobic respiration alone.