So let's suppose in our mixture, we have a total of 100 enzymes, and each one of these enzymes will have its own active site. Now, if we add 50 substrate molecules, that only 50 enzymes will contain active sites that are filled. And that means our entire mixture, because only half of the enzymes are filled, the entire activity of all the enzymes will be half of its maximum value. But if we continue adding substrate molecules so that we add, let's say, 100 substrate molecules, then all the active sites and all the enzymes will be filled. And that means the entire activity of our mixture of enzymes will be at a maximum velocity. And that's exactly what this graph actually represents.