Beta-oxidation of fatty acids occurs in

The correct option/answer is: Mitochondria.

Step-by-step Explanation:

1. Understanding Beta-Oxidation:
Beta-oxidation is the metabolic process by which fatty acid molecules are broken down in mitochondria and/or peroxisomes to generate acetyl-CoA, which enters the citric acid cycle, and NADH and FADH₂, which are co-enzymes used in the electron transport chain.

2. Primary Site in Animal Cells:
In animal cells, the majority of beta-oxidation of short-chain, medium-chain, and long-chain fatty acids occurs inside the matrix of the mitochondria. This allows the produced acetyl-CoA to directly enter the citric acid cycle (Krebs cycle) to generate ATP efficiently within the same organelle.

3. Peroxisomes vs. Mitochondria:
While peroxisomes also perform beta-oxidation, they specifically target very-long-chain fatty acids (VLCFAs) and branched-chain fatty acids, shortening them until they can be fully oxidized by the mitochondria. However, the standard and major site for general beta-oxidation of fatty acids in animal metabolism is recognized as the mitochondria.