Final answer:
The Krebs cycle is a series of chemical reactions that occur in the mitochondria and is a part of aerobic cellular respiration. Each molecule of glucose that enters the cycle produces two molecules of acetyl CoA, resulting in the production of three molecules of NADH and one molecule of FADH2. In the absence of oxygen, pyruvate is converted to lactate in a process called fermentation.
Step-by-step explanation:
The Krebs cycle, also known as the citric acid cycle or the tricarboxylic acid (TCA) cycle, is a series of chemical reactions that occur in the mitochondria of cells. It is an integral part of aerobic cellular respiration, which is the process by which cells convert glucose into energy.
During the Krebs cycle, each molecule of glucose that enters the cycle produces two molecules of acetyl CoA, which then enter the cycle. Each molecule of acetyl CoA goes through the cycle once, resulting in the production of three molecules of NADH and one molecule of FADH2. These energy-carrying molecules will be used later in the process to produce ATP.
In the absence of oxygen, the Krebs cycle cannot occur, as it requires oxygen as the final electron acceptor. Instead, pyruvate, the product of glycolysis, is converted to lactate in a process called fermentation. This allows the regeneration of NAD+ so that glycolysis can continue without the need for external NAD+.