Question

which is the universal source of energy in all cells

Answer 1

ATP is just adenosine attached to three phosphates: 
A - P - P - P 

The bond between A - P - P and the last P is unstable and can store energy so that when the bond is broken, energy is released.. 

A - P - P is adenosine diphosphate (ADP) 

ATP --> ADP + P + energy

Answer 2

ATP (adenosine triphosphate ) is the universal source of energy in all cells. It is produced in the mitochondria (power house of the cell).It gives energy to cells so it's known as energy currency.