Explain why a graph showing the substrate concenentration and rate of reaction for an enzyme catalysed reaction plateaus?

Initally, the rate of reaction is able to increase as concentration does because at this point, not all enzymes active sites are occupied. Therefore, by adding more substrate, a higher percentage of enzymes are able to be put to work. However, if the concentration is increased to the saturation point or above it, a graph showing the reaction will plateau. This is because the substrate is now in excess and 100% of the active sites are full. The enzyme at this point is therefore the limiting factor for increasing the rate of reaction