5. what molecule is essential to regenerate at the end of the krebs cycle to start the process again? a. water b. pyruvate c. oxaloacetate d. ammonia

Oxaloacetate

Explanation: The krebs cycle starts with the pyruvic acid that is obtained after glycolysis. The Kreb's cycle begins when the Acetyl coA combines with a four molecule oxaloacetate.

The main product formed is citric acid thats why the cycle is also called as citric acid cycle. After the citric acid is formed it goes through a series of reactions to form NADH, FADH2 and ATP.

The carbon dioxide is also released during this process. The oxaloacetate formed is used to start the cycle so its is regenerated again and again.

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