Final answer:
The mitochondrion is responsible for the tricarboxylic acid cycle enzyme reactions, electron transport, and ATP synthesis.
Step-by-step explanation:
The mitochondrion is responsible for multiple functions, making option 4) All of the choices are correct. In the mitochondrion, the tricarboxylic acid cycle enzyme reactions, also known as the Krebs cycle or citric acid cycle, occur. This cycle generates high-energy molecules such as ATP, NADH, and FADH2. The mitochondrion also carries out electron transport, where NADH and FADH2 pass electrons through the electron transport chain to generate more ATP. Lastly, in the mitochondrion, ATP synthesis takes place, which is the production of adenosine triphosphate, the cell's main energy-carrying molecule.