Final answer:
The ER membrane is more fluid than the plasma membrane due to its high content of unsaturated phospholipids, which inhibit tight packing and promote curvature. This fluidity facilitates the ER's functions in protein and lipid synthesis, carbohydrate metabolism, and detoxification. The correct option is B.
Step-by-step explanation:
The endoplasmic reticulum (ER) membrane is typically more fluid than the plasma membrane due to its unique composition.
The ER membrane is more fluid because it contains mainly unsaturated phospholipids, which have kinks in their fatty acid tails that prevent the lipids from packing tightly together. This increased fluidity allows for more curvature in the membrane structure.
In contrast, sphingolipids, which are more common in the plasma membrane, tend to promote a more rigid structure. While cholesterol is present in the ER membrane, it does not exist in as high concentrations as in the plasma membrane, which also contributes to the fluidity difference.
The ER membrane's distinct composition supports its role in the synthesis of proteins and lipids, as well as in facilitating various other cellular processes such as carbohydrate metabolism and detoxification of toxic compounds.
The rough endoplasmic reticulum (RER) is studded with ribosomes and involved in protein synthesis, while the smooth endoplasmic reticulum (SER) is more focused on lipid biosynthesis and does not have ribosomes on its surface.The correct option is B.