How does the cell regulate the number of mitochondria in a cell? What happens when there are too many or too few?
The concept you refer is recognized as mitochondrial biogenesis and it is regulated by AMPK which senses the cellular energy demand. If you have few mitochondria in the cell, the electron transport chain works suboptminally generating less ATP. When the AMP/ATP ratio is high (low ATP) AMPK is activated, and turns on the catabolic pathways required to produce more ATP, included mitochondrial biogenesis.