Areducing chemical reaction
reduces the compound to a simpler form
adds an electron to the substrate
removes a hydrogen atom from the substrate
is a catabolic reaction

Adds an electron to the substrate.

Explanation:

A reducing chemical reaction add an electron to the substrate as, the oxidation in the chemical reaction by which there is loses in the electron of the substrate and during the reduction there is gain of electron in the substrate. So, during the loss of electron in the substrate in the oxidation process, on the other hand there is add of electron in the substrate during the reduction process.

littering streams           is the answer