The tube network in the cytoplasm where cell substances are made is called the endoplasmic reticulum (ER).

Here's why:

* Network of Membranes: The ER is a vast network of interconnected membranes that extend throughout the cytoplasm of eukaryotic cells.

* Synthesis and Modification: The ER plays a crucial role in the synthesis of proteins, lipids, and steroids.

* Rough ER: Ribosomes attach to the surface of the rough ER, making it the site of protein synthesis and modification.

* Smooth ER: The smooth ER lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage.

Let me know if you'd like more details about the ER's functions!