The reabsorption process in various segments of the nephron. The little children playing the game each have a fishing pole with an attached magnet to catch the fish as they move by. Different colored fish have different prize values associated with them, so some children will be selective and try to grab the colored fish with the highest prize value. Now suppose our nephron is the stream, the filtered molecules are the various colored fish, and our children are the transporters. Furthermore, each child is fishing for a specific colored fish.
Most children start at the beginning of the stream and some spread out further downstream.
By the end of the stream, most of the fish have been caught. This is what happens as the filtrate travels through the nephron. Like our children in the fish pond game, if you increase the number of fish in the stream, the children will have an easier time catching them. There is a limit to how many molecules the transporters can grab in a given period of time. Rate of flow of the filtrate - flow rate affects the time available for the transporters to reabsorb molecules.