Here's what that means:

* Phospholipids: These are special types of fats that have a "head" and two "tails".

* The head is hydrophilic (water-loving) and faces the watery environment inside and outside the cell.

* The tails are hydrophobic (water-fearing) and point inwards, forming the middle layer of the membrane.

* Bilayer: This means there are two layers of phospholipids arranged back-to-back. The hydrophobic tails of one layer face the hydrophobic tails of the other layer.

Think of it like a sandwich:

* Bread slices: The hydrophilic heads of the phospholipids are like the bread, facing the watery environments.

* Filling: The hydrophobic tails are like the filling, sandwiched between the bread and not interacting with water.

Key functions of the cell membrane:

* Barrier: It separates the inside of the cell from the outside environment.

* Selectively permeable: It controls what enters and leaves the cell. This is important for maintaining the cell's internal environment.

* Communication: It has proteins embedded within it that allow cells to communicate with each other and their environment.

In addition to the phospholipid bilayer, the cell membrane also contains:

* Cholesterol: This helps to maintain the fluidity and stability of the membrane.

* Proteins: These play a variety of roles, including transporting molecules, receiving signals, and anchoring the membrane to the cytoskeleton.

So, the cell membrane is more than just a simple barrier. It's a dynamic structure that is essential for the life of the cell.