Answer:
The plasma membrane is a thin layer of lipid molecules that surrounds the cell and separates the inside from the outside. The fluid mosaic model describes the structure of the plasma membrane as a two-layered structure of phospholipids with embedded proteins. This model explains how the structure of the plasma membrane allows it to act as a selective barrier, regulating the movement of substances in and out of the cell.
Structure S in the plasma membrane is represented by the phospholipids, which form a lipid bilayer with hydrophilic heads facing outwards and hydrophobic tails facing inwards. The hydrophilic heads are in contact with the extracellular fluid and intracellular fluid while the hydrophobic tails are in the middle of the membrane. The phospholipid bilayer provides a barrier that separates the inside and outside of the cell, restricting the movement of hydrophilic and large molecules through the membrane while allowing the passage of small and hydrophobic molecules.
Structure T represents the integral membrane proteins that are embedded in the lipid bilayer. These proteins have different functions, such as transport of molecules, cell signaling, and catalyzing chemical reactions. The proteins also contribute to the selective permeability of the membrane by regulating the movement of specific molecules in and out of the cell. For example, channels and carrier proteins regulate the movement of ions and larger molecules through the membrane while receptor proteins receive signals from the outside of the cell and relay them to the inside of the cell.
In summary, the plasma membrane is mainly composed of phospholipids and proteins according to the fluid mosaic model. The phospholipids form a lipid bilayer that acts as a barrier, while the proteins embedded in the bilayer regulate the selective permeability of the membrane by facilitating the movement of specific molecules in and out of the cell.
Step-by-step explanation: