The membrane of the endoplasmic reticulum is continuous with which structure?

1. The ER membrane is a phospholipid bilayer embedded with proteins. 2. It is continuous with the nuclear envelope, so the two form one connected membrane surface. 3. That continuity is why ribosomes are found on the outer membrane of the nuclear envelope as well as on the ER. 4. Mitochondrial and chloroplast membranes are excluded from the endomembrane system altogether, so neither can be continuous with the ER. 5. The ER is continuous with the nuclear envelope. 6. A lysosome buds off as a separate sac, so it is joined to the system by traffic rather than by continuous membrane. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 4 "Cell Structure", section 4.4 The Endomembrane System and Proteins_