Concept:The cell membrane is built on a phospholipid bilayer, with proteins attached to or embedded within it.
Explanation:According to the fluid mosaic model, the membrane is a flexible, dynamic structure rather than a rigid one.
A phospholipid bilayer provides the central structural framework of the cell membrane.
The hydrophilic phosphate heads face the aqueous environments outside and inside the cell, while the hydrophobic fatty acid tails face each other in the interior.
Protein molecules are located on the outer surface, on the inner surface, or partially embedded inside the lipid bilayer.
These proteins serve various functions such as transport, recognition, and support.
Therefore, the membrane is best described as a middle lipid bilayer with a protein layer on either surface.
Answer:C. middle bi-layer of lipid with a protein layer on either surface