In an enzyme controlled reaction, a substrate is the same as

In an enzyme controlled reaction, a substrate is the same as a reactant.

Reactant is a substance that will be used (there will be reduced) in reaction. Substrate will bind with enzyme and undergo a chemical reaction, so it will be used to make the product. Catalyst is helping reaction but not used, thus it's not a reactant. 

What is the example? i’ll be happy to answer if you can tell me : )

Organism, organ system, organs, tissue, cells