The energy a cell needs to build molecules or to power cellular respiration is supplied by

The energy a cell needs to build molecules or to power cellular respiration is supplied by mitochondria.

Explanation:

Mitochondria  are tiny cell organelle present in eukaryotic cells. It is called the powerhouse of the cell. It is referred to as such because it produces most number of energy molecules or ATP that is released from food. It produces 36 molecules of ATP and the cell produces 2 molecules of ATP. This process of releasing energy from food by the mitochondria is called cellular respiration. These energy molecules are then used in various other cellular activities.