It is a system of flattened, interconnected canals and sacs wrapped in a membrane. The production, storage and transport of some substances takes place in this organelle. It also provides internal support. Although the endoplasmic reticulum is present in most eukaryotic cells, it is not found in red blood cells or sperm. There are two types of endoplasmic reticulum, smooth and rough. The latter has that appearance because it has ribosomes attached to its surface. However, these ribosomes are not a structural part of the reticulum, since they freely adhere to or detach from the membrane.