The series of folded membranes that move materials around in a cell is called the endoplasmic reticulum (ER).

Here's a breakdown:

* Endoplasmic Reticulum (ER): This is a network of interconnected membranes that extend throughout the cytoplasm of eukaryotic cells. It is responsible for:

* Protein Synthesis and Modification: The rough ER, studded with ribosomes, is the site of protein synthesis. It also folds and modifies proteins for proper function.

* Lipid and Steroid Synthesis: The smooth ER, lacking ribosomes, synthesizes lipids, steroids, and other important molecules.

* Detoxification: The smooth ER plays a role in detoxifying harmful substances.

* Calcium Storage: The ER stores and releases calcium ions, which are essential for various cellular processes.

* Transport: The ER acts as a network of internal highways, moving molecules throughout the cell.

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