Final answer:
The nuclear membrane is indeed part of the endomembrane system since it is continuous with the ER. Meanwhile, mitochondria and chloroplast membranes are not included in this system as they hail from an endosymbiotic origin.
Step-by-step explanation:
The endomembrane system is composed of several interconnected organelles that collaborate to modify, package, and transport lipids and proteins. These include the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vesicles, and the plasma membrane. However, structures such as the mitochondria and chloroplast membranes are not part of this system. To answer the question directly, the nuclear membrane is considered a part of the endomembrane system since it is continuous with the endoplasmic reticulum, which is an organelle of the endomembrane system. Conversely, structures like ribosomes and centrosomes are not part of this system. Furthermore, the membranes of mitochondria or chloroplasts are excluded from the endomembrane system as they are likely derived from an endosymbiotic bacterium.