Fact 1: Microbial fuel cells convert chemical energy into electrical energy.

Fact 2: Electrical energy refers to energy associated with the flow of electrons.

Given the two facts above, answer the question "what do microbial fuel cells convert chemical energy into?" with the following options: 
- rays or beams
 - transportation technology
 - Deoxyribonucleicacid
 - flow of electrons
 - hydrogen and oxygen
 - deoxyribonucleic acid
 - an engine
 - heating liquids


 

    flow of electrons     