Biology

The correct answer is: A.Phospholipid bilayer

In the fluid mosaic model of the cell membrane, the "fluid" part refers to the phospholipid bilayer. This bilayer is composed of phospholipids, and the hydrophobic tails of these molecules are free to move around within the bilayer, allowing the membrane to be flexible and dynamic. The "fluid" nature allows proteins and other molecules embedded within the bilayer to move laterally, which is important for membrane function, including signaling, transport, and cell communication.

Here’s why the other options are not the "fluid" part:

B.Proteins embedded in the membrane: Proteins are embedded in the membrane, but they are not the "fluid" ...