The organelle that moves proteins and other substances through the cell is the endoplasmic reticulum (ER).

Here's why:

* Rough ER: This portion of the ER is studded with ribosomes, which are the sites of protein synthesis. Proteins made by ribosomes on the rough ER are then folded and transported within the ER lumen (the space inside the ER).

* Smooth ER: This portion of the ER lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage.

The ER acts like a transportation network within the cell, moving substances from one part of the cell to another, and even to the cell membrane for export.