Which organelle do you think would kill you the fastest if you lost it?

The answer is mitochondrion. Mitochondria are critical for the cell's biochemical processes that require energy to be powered. Mitochondria are responsible for generating this power in the form of ATP through a process called chemiosmosis. Without ATP, the cell would immediately die since it would be incapable of performing virtually all biochemical processes that re required to sustain life.