Which cell membrane is a superimposed elastic sac of ER-like thickness, which helps in processing and packaging protein and lipid molecules, especially stable proteins?

Golgi apparatus

The correct answer is Option (2) – Golgi apparatus

The cell membrane described as a "superimposed elastic sac of ER-like thickness, which helps in processing and packaging protein and lipid molecules, especially stable proteins" refers to the Golgi apparatus.

The Golgi apparatus is a cellular organelle found in eukaryotic cells responsible for modifying, sorting, and packaging proteins and lipids for transportation to various destinations within the cell or for secretion outside of the cell. It consists of a series of flattened membrane-bound sacs, similar to a stack of pancakes, often referred to as cisternae. These sacs are superimposed and vary in thickness, resembling the endoplasmic reticulum (ER) in structure.

The Golgi apparatus receives proteins and lipids from the endoplasmic reticulum and modifies them by adding sugars, lipids, or phosphate groups, and then sorts and packages these molecules into vesicles for transport to their final destinations. It plays a crucial role in cellular secretion, the formation of lysosomes, and the synthesis of cell wall components in plant cells.