Pick your answer from: (I) nucleus (II) cell wall (III) plastid (IV) cell membrane

Answer the following question given this paragraph: Carrier proteins bind and carry the molecules across the cell membrane. These proteins bind a molecule on one side of the membrane, change shape as they carry the molecule across the membrane, and deposit the molecule on the other side of the membrane. Even though a protein is involved in both these methods of transport, neither method requires energy. Therefore these are still types of passive transport. Q: Carrier proteins bind and carry the molecules across what cell structure? A:
Answer:
(IV)