So what that basically means is at the beginning of that chemical reaction we see that the rate, the velocity of that enzymes activity is directly proportional to the substrate concentration. So that is what we mean by a first order reaction. So notice that this is a straight line and also a first order reaction. And this implies that the rate of the reaction is directly proportional to the substrate concentration at the beginning of that chemical reaction. So this equation correctly describes the behavior at the beginning of that chemical reaction. Now what about at the end of the chemical reaction?