Final answer:
The endomembrane system includes components like the nuclear envelope, ER, Golgi apparatus, lysosomes, vesicles, and the plasma membrane. Mitochondria are not part of this system and thus, 'Mitochondria' is the correct answer to the question which component is not part of the endomembrane system.
Step-by-step explanation:
The endomembrane system is an integral part of eukaryotic cells, involved in the synthesis, modification, packaging, and transport of proteins and lipids. It includes several components, such as the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vesicles, and the plasma membrane. These structures work together to ensure the proper functioning of the cell. Mitochondria, however, are not considered to be a part of the endomembrane system. This is because the endomembrane system does not include either mitochondria or chloroplast membranes. Given the options a) Endoplasmic reticulum, b) Golgi apparatus, c) Mitochondria, and d) Vesicles, the correct answer to which of these is not a component of the endomembrane system is c) Mitochondria.