Endoplasmic reticulum is of how many types?

1. ER comes in rough and smooth forms. 2. Rough ER has ribosomes attached and makes proteins. 3. Smooth ER lacks ribosomes and synthesises lipids. 4. So there are two types of ER. _Source: Selina Concise Biology ICSE Class 10, Ch 1 'Cell, the Structural and Functional Unit of Life'_