Organelle identification — A double phospholipid bilayer with numerous large pores most likely indicates the nuclear envelope

Introduction:
Many organelles are bounded by membranes, but their architecture differs. This question probes recognition of a unique hallmark: a double membrane that is perforated by many large proteinaceous pores allowing regulated macromolecular exchange with the cytoplasm.

Given Data / Assumptions:

• The structure has two lipid bilayers (a double membrane).
• It contains numerous large pores visible at suitable resolution.
• Context is a typical eukaryotic cell.

Concept / Approach:
The nuclear envelope comprises an inner and outer membrane, continuous with the rough endoplasmic reticulum. Large nuclear pore complexes traverse both membranes to mediate selective transport of RNAs and proteins.

Step-by-Step Solution:

Verification / Alternative check:
Electron micrographs show nuclear pore complexes as large octagonal assemblies (~100 nm scale) that allow passive diffusion of small solutes and active transport of large cargo via nucleoporins.

Why Other Options Are Wrong:

• Plasma membrane: single bilayer, lacks large trans-envelope pores of this type.
• Mitochondrion: double membrane but has specialized channels; not studded with many large pores.
• Cytoskeleton: not a membrane at all; a protein fiber network.
• Chloroplast envelope: double membrane, but again not perforated by numerous large nuclear-style pores.

Common Pitfalls:
Equating any double membrane with the nucleus; pore abundance and continuity with rough ER are decisive clues.

Final Answer:
the nuclear envelope.