Which of the following statement(s) is/are true concerning cellular ion channels?

a. Ion channels are transmembrane proteins that form pores that can conduct ions across the plasma membrane

b .Ion channels are formed by membrane-spanning peptides that are arranged so that polar moieties line a central core

c. Ion channel proteins undergo conformational changes between open states and closed states 

d. Ion channels can be blocked

Ion channels are transmembrane proteins that form pores that can conduct ions across the plasma membrane. Ion channels are formed by membrane-spanning peptides that are arranged so that polar moieties line a central pore. These polar groups take the place of the water of hydration, which stabilizes an ion in an aqueous solution creating, in essence, a water-like environment into which the ion can partition and move in the presence of the appropriate driving force. Ion channels are permissive transport elements. Ions flow through a channel only through the presence of an appropriate driving force. Ion channels do not conduct all the time, rather the channel protein undergoes conformational changes between a conducting (open) state and nonconducting (closed) state. These conformational changes are collectively referred to as gating. The conduction process can also be blocked by ions or organic compounds that enter the channel, bind there, and occlude the pore.