Structure of the chloroplasts Chloroplast Thylakoids(类囊体): the thylakoid membrane is highly impermeable to ions and other metabolites because its function is to establish the proton motive force necessary for ATP synthesisStructure of the chloroplasts • Thylakoids(类囊体):the thylakoid membrane is highly impermeable to ions and other metabolites because its function is to establish the proton motive force necessary for ATP synthesis