Concept: The nuclear envelope is a double membrane that requires gated channels to allow macromolecules to enter and exit.

Solution: The nuclear envelope is punctuated by large protein complexes called nuclear pores. These pores strictly regulate the exchange of materials, allowing RNA and ribosomal subunits to exit into the cytoplasm, and necessary proteins (like polymerases) to enter the nucleus.

Distractor Autopsy: The nucleoplasm is the fluid inside. The nuclear lamina provides structural support. The nucleolus synthesizes rRNA.