Final answer:
The endoplasmic reticulum is the major site of new membrane synthesis in a cell. It is involved in the synthesis and transport of lipids and proteins.
Step-by-step explanation:
The major site of new membrane synthesis in a cell is the endoplasmic reticulum. The endoplasmic reticulum is an organelle involved in the synthesis and transport of lipids and proteins. It consists of a network of membrane-bound tubes and sacs, where new membranes are made and then transported to other parts of the cell. The endoplasmic reticulum plays a crucial role in cell function by providing a site for the production of new membranes and facilitating intracellular transport.