Answer:
Mitochondria
Step-by-step explanation:
The mitochondrion is a relatively small, double membrane organelle that primarily serves as the site of oxidative phosphorylation; a process that generates energy in the form of ATP for the running of cell's activities.
Hence, a cell that requires a lot of energy might need a large number of mitochondria in order to meet the energy demand of the cell.
The answer is mitochondria.