Final answer:
The nuclear envelope, a double-membrane structure, separates its inner and outer phospholipid bilayers, with nuclear pores regulating the transport between the nucleoplasm and cytoplasm.
Step-by-step explanation:
The two parts that are separated by the glass or metal envelope, as referred to in the context of cell biology, are the inner and outer membranes of the nuclear envelope. The nuclear envelope is a double-membrane structure that serves as the outermost boundary of the nucleus in eukaryotic cells. It is composed of two phospholipid bilayers, with the outer membrane being continuous with the rough endoplasmic reticulum. The nuclear envelope also contains nuclear pores which are essential for the transport of materials such as RNA and proteins between the nucleoplasm within the nucleus and the cytoplasm outside it. This exchange is tightly regulated by the nuclear pore complexes. The inner and outer membranes, despite being contiguous, feature unique sets of lipids and proteins, and together maintain the integrity and function of the nucleus in cellular processes.