Final answer:
The nucleus's nuclear envelope, punctuated with nuclear pores, regulates the passage of large molecules like mRNA between the nucleoplasm and the cytoplasm.
Step-by-step explanation:
The organelle in question is the nucleus, specifically the structure known as the nuclear envelope. This double membrane is integral to the nucleus and is characterized by the presence of nuclear pores. These pores are essential for the regulation of molecules such as mRNA that travel between the nucleoplasm and the cytoplasm.
The nuclear envelope serves as a barrier and a gateway for the transport of substances. It features two lipid bilayers with a fluid space in between and is punctuated with nuclear pores. These pores are equipped with pore complexes that allow the selective passage of large molecules like proteins and RNA while maintaining the necessary isolation of genetic material within the nucleus. The nucleoplasm, where we find the chromatin and nucleolus, is the semi-solid fluid inside the nucleus, separated from the cytoplasm by the nuclear envelope.