The organelle that forms passageways throughout the cell is the endoplasmic reticulum (ER).

There are two types of ER:

* Rough ER: Has ribosomes attached to its surface and is involved in protein synthesis and modification.

* Smooth ER: Lacks ribosomes and plays roles in lipid synthesis, detoxification, and calcium storage.

Both types of ER form a network of interconnected membranes that extend throughout the cytoplasm, creating a system of passageways for the transport of molecules within the cell.