Final answer:
The exception to pathways active during fatty acid biosynthesis is B-oxidation, as it is part of the catabolic processes that break down fatty acids, in contrast to the anabolic process of fatty acid synthesis.
Step-by-step explanation:
The exception to metabolic processes expected to be active during fatty acid biosynthesis is B-oxidation. Fatty acid biosynthesis is a constructive metabolic process where fatty acids are synthesized, while B-oxidation is a catabolic process in which fatty acids are broken down into acetyl-CoA in the mitochondria. B-oxidation is actually the inverse process of fatty acid synthesis.
Therefore, during the biosynthesis of fatty acids, B-oxidation would not be active because it is a part of fatty acid catabolism, not synthesis. On the other hand, the Tricarboxylic Acid Cycle, also known as the Krebs cycle or Citric Acid Cycle, and the Pyruvate Dehydrogenase Complex are both involved in providing the necessary precursors such as acetyl-CoA and NADPH for fatty acid synthesis.
Glycolysis is the metabolic process that breaks down glucose and provides pyruvate, which is further processed into acetyl-CoA that enters the fatty acid synthesis pathway. Furthermore, some amino acids from amino acid catabolism can also contribute to the pool of acetyl-CoA and NADPH required for fatty acid synthesis.