Adding substrates will NOT make a difference to the enzyme catalysed reaction:

Explanation

The rate of an enzyme-catalysed reaction increases with substrate concentration only until all the enzyme's active sites are occupied. Once most of the enzyme molecules are saturated with substrate, the reaction reaches its maximum rate (Vmax). Beyond this point, adding more substrate does not increase the rate because there are no free enzyme molecules left to bind with it.If many enzymes are still unsaturated, adding substrate will still increase the rate. But when only a few enzyme molecules are unsaturated (i.e., almost all are occupied), adding more substrate makes no difference.