Question

based of the fluid mosaic model of cell membranes, which of the following statements about membrane phospholipids is true?

they can move laterally along the plane of the membrane.

they frequently flip - flop from one side to the membrane to the other.

they occur in an uninterrupted bilayer, with membrane proteins restricted to the surface of the membrane.

they frequently leave the bilayer and dissolve in the surrounding solution.

Explanation:

• Fluid mosaic model: The cell membrane is composed of a phospholipid bilayer with embedded proteins. Phospholipids have a hydrophilic head and hydrophobic tails.
• Lateral movement: Phospholipids can move laterally (side - to - side) within the plane of the membrane due to the fluid nature of the lipid bilayer. This movement is relatively common and allows for membrane fluidity.
• Flip - flop movement: Flip - flop (transverse) movement of phospholipids (from one leaflet of the bilayer to the other) is rare. It requires the hydrophilic head to pass through the hydrophobic core of the membrane, which is energetically unfavorable without the help of specific enzymes (flippases).
• Membrane proteins: Membrane proteins are not restricted to the surface. Integral membrane proteins can span the entire bilayer (transmembrane proteins), while peripheral membrane proteins are associated with the surface. So, the statement about an uninterrupted bilayer with proteins only on the surface is incorrect.
• Leaving the bilayer: Phospholipids are part of the bilayer and do not frequently leave it to dissolve in the surrounding solution. The hydrophobic interactions between the tails and the aqueous environment (both inside and outside the cell) keep them in the bilayer.

Answer:

they can move laterally along the plane of the membrane.