Question

Aerobic cellular respiration depends on the presence of O2 for ATP synthesis. However, cells can also synthesize ATP without oxygen. Which of the following mechanisms can generate ATP in the absence of oxygen?

Answer 1

Cells can synthesize ATP without oxygen via anaerobic respiration and fermentation, which involve only glycolysis leading to lactic acid or alcoholic fermentation.

Step-by-step explanation:

Mechanisms that can generate ATP in the absence of oxygen include anaerobic respiration and fermentation. These processes only utilize glycolysis to synthesize ATP, bypassing the need for oxygen. During glycolysis, one molecule of glucose is partially oxidized, producing a net gain of two ATP molecules. In fermentation, conversion to either ethanol or lactate occurs, which allows the recycling of NADH into NAD+, enabling glycolysis to continue producing ATP.

In lactic acid fermentation, which occurs in human muscle cells under strenuous activity, pyruvate is converted into lactate. In alcoholic fermentation, commonly used by yeast and some kinds of bacteria, pyruvate is transformed into alcohol and carbon dioxide. While these processes produce less ATP than aerobic respiration, they are crucial for survival in environments lacking oxygen.