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Cell Membrane – Structure and Function

Composition of the Cell Membrane & Functions

The cell membrane is also called the plasma membrane and is made of a phospholipid

bilayer (A). Some of the functions of the cell membrane include protecting and enclosing the

cell, giving shape to the cell, allowing transportation of materials in and out of the cell, and

carry out metabolic reactions near the inner surface of the cell membrane. The phospholipids

of the cell membrane have a “hydrophilic” (water loving/attracting) head (G) and two

“hydrophobic” (water fearing/repeling) tails (F). The head of a phospholipid is made of an

alcohol and phosphate group, while the tails are chains of fatty acids.

The cell membrane is constantly vibrating, creating small openings within the structure.

Therefore, the phospholipids can allow water and other smaller molecules to pass through into

or out of the cell, without the use of energy. This type of passive transport is known as

diffusion because the molecules are moving with the concentration gradient (highlow).

Another type of lipid in the cell membrane is cholesterol (I) that makes the membrane

more fluid and adds to its flexibility. Embedded in the phospholipid bilayer are proteins that

also aid in diffusion and in cell recognition. Proteins called transport proteins (B) go all the way

through the bilayer. Integral proteins, also known as membrane proteins (H), are found only on

one side of the membrane. Large molecules like glucose utilize these channel proteins to help

move across cell membranes without the use of energy. Some membrane proteins, called

glycoproteins (C), have carbohydrate chains (E) attached to help cells recognize each other and

certain molecules.

1. What is another name for the cell membrane? Generally speaking, identify the overall structure

of the cell membrane.

2. Define hydrophilic. Which portion of the bilayer is hydrophilic?

3. Define hydrophobic. Which portion of the bilayer is hydrophobic?

4. When does the movement of materials in and out of the cell NOT require energy?

5. List the responsibilities of the cell membrane?

6. Describe the function of the proteins embedded in the cell membrane?

7. How are cells able to recognize various molecules and other types of cells?

Cell Membrane - Structure And Function