The puzzle piece that fits inside an enzyme is called

The answer would be Substrates

Enzymes bind with chemical reactants called substrates.

Explanation:

Enzymes bind with chemical reactants called substrates.

primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs