Solved by a verified expert:tosisis specificREcepters in ECM/membrane. substances pass, recepter binds them. Cell knows it has to pick them up, so in folds in and brings them in.-this takes a lot of energy so cells do this very little (for example when they see a lot of cholesterol, they take in)them. Cell knows it has to pick them up, so in folds in and brings them in.-this takes a lot of energy so cells do this very little (for example when they see a lot of cholesterol, they take in)