Concept:The cell organelle that forms a membrane network for transporting materials within the cytoplasm is the endoplasmic reticulum.
Explanation:The endoplasmic reticulum is made up of folded membranes that extend through the cytoplasm.
It creates channels that convey proteins and other materials from one part of the cell to another.
The plasma membrane forms the outer boundary of the cell.
The nuclear membrane surrounds the nucleus only.
The mitochondrion is mainly responsible for energy production, not transport.
Therefore, the organelle described in the question is the endoplasmic reticulum.
Answer:D. endoplasmic reticulum