In contrast, a channel can be open to both environments at the same time, allowing the solutes it transports to diffuse without interruption. Carriers have binding sites, but pores and channels do not.[5][6][7] When a channel is opened, millions of ions can pass through the membrane per second, but only 100 to 1000 molecules typically pass through a carrier molecule in the same time.[8] Each carrier protein is designed to recognize only one substance or one group of very similar substances. Research has correlated defects in specific carrier proteins with specific diseases.[9]