Final answer:
The structure that is not part of the endomembrane system among the provided choices is c) Mitochondria. The endomembrane system includes the nuclear envelope, ER, Golgi apparatus, lysosomes, and various vesicles, but not the mitochondria, which play a key role in energy production and have their own unique double-membraned structure.
Step-by-step explanation:
Among the choices provided, the structure that is not part of the endomembrane system is c) Mitochondria.
The endomembrane system is comprised of several interconnected organelles that function to modify, package, tag, and transport proteins and lipids integral to the cell's membrane system. Included in this system are the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, and various types of vesicles. It is also connected with the plasma membrane.
The mitochondria, however, are not part of the endomembrane system. These organelles have a distinct role in cellular respiration and energy production. They have their own double membrane; the inner one folds into cristae and contains its own mitochondrial DNA, separate from the DNA in the nucleus of the cell.
On the other hand, the endoplasmic reticulum is involved in the synthesis and folding of proteins, as well as lipid metabolism. The Golgi apparatus modifies, sorts, and packages proteins and lipids received from the ER for transport to different destinations. Lysosomes contain enzymes that break down cellular waste, and the plasma membrane encloses the cell, controlling what enters and exits.