Substrate Concentration
The relationship between substrate concentration and rate id very similar to the relationship between enzyme concentration and rate. There are some subtle differences.
Again, at low concentrations threat is directly proportional to concentration. However if you simply keep increasing the substrate concentration but keep the enzyme concentration the same you will eventually reach a situation were all the enzymes are already 'busy' and the substrate cannot collide with an 'available' enzyme. At this point the saturation point has been reached and the reaction cannot go any quicker by increasing substrate concentration.
Again, at low concentrations threat is directly proportional to concentration. However if you simply keep increasing the substrate concentration but keep the enzyme concentration the same you will eventually reach a situation were all the enzymes are already 'busy' and the substrate cannot collide with an 'available' enzyme. At this point the saturation point has been reached and the reaction cannot go any quicker by increasing substrate concentration.