The network of double membrane that conveys materials through the cytoplasm is the

Step 1: Analyze the question The question asks for the cell structure that is a network of double membranes which transports materials through the cytoplasm.

Step 2: Explain the concept The endoplasmic reticulum (ER) is a system of flattened sacs and tubes (cisternae) made of membranes, running throughout the cytoplasm. It is continuous with the nuclear envelope. Its main functions are:

• Rough ER (with ribosomes): makes and transports proteins.
• Smooth ER: makes lipids and transports materials, and in the liver it helps with detoxification.

Because its membrane layers form channels, it acts as the cell's "transport system" or "highway."

Step 3: Check each option

• A. Plasma membrane: this is the outer boundary of the cell. It controls what enters and leaves, but it is not a network inside the cytoplasm.
• B. Nuclear membrane: this surrounds the nucleus and controls movement into and out of it. It is not a network spread through the cytoplasm.
• C. Mitochondrion: this is the site of aerobic respiration, where energy (ATP) is released. It has a double membrane but is not a transport network.
• D. Endoplasmic reticulum: this is a membrane network that conveys materials through the cytoplasm, so it fits the description.

Step 4: Answer The correct option is D. Endoplasmic reticulum.

Exam tip: Think of "reticulum" as meaning "network" (like a net). When you see "network" and "transport within the cytoplasm" together, it points to the ER. Remember: ER = Eco-Route for moving materials around the cell.