It is absent in prokaryotes.
Explanation
The nuclear membrane, also known as the nuclear envelope, is a specialized double-membrane structure that encloses the nucleus in eukaryotic cells. It serves as a barrier separating the genetic material (DNA) from the cytoplasm. The presence or absence of this structure is a primary distinction between different types of cells.
Statement-wise Analysis
- Statement It is single-layered in eukaryotes. is Incorrect. In eukaryotes, the nuclear membrane is a double-layered structure. It consists of two concentric lipid bilayers: the inner nuclear membrane and the outer nuclear membrane.
- Statement It is absent in prokaryotes. is Correct. Prokaryotic organisms (such as bacteria) lack membrane-bound organelles. They do not possess a defined nucleus or a nuclear membrane. Instead, their genetic material is found in a region of the cytoplasm known as the nucleoid.
- Statement It is impermeable to all substances. is Incorrect. The nuclear membrane is not impermeable to all substances. It is punctuated by nuclear pores, which regulate the selective transport of large molecules like RNA and proteins between the nucleus and the cytoplasm.
- Statement It is continuous with the plasma membrane. is Incorrect. The outer nuclear membrane is continuous with the membrane of the Endoplasmic Reticulum (ER), not the plasma membrane. The plasma membrane is the outer boundary of the cell itself.
Key Takeaway
The nuclear membrane is a double-layered envelope found only in eukaryotes. It contains pores for transport and is continuous with the Endoplasmic Reticulum. Prokaryotes completely lack a nuclear membrane.