Name__________________________________ Date_________ Block_________
Cell Membrane Information Worksheet
Composition of the Cell Membrane & Functions
The cell membrane is also called the plasma membrane. It is made of a
phospholipid bilayer. This double layer of lipids is also known as a fluid mosaic
because the phospholipids that make up the membrane lie next to each other but are
not connected. This gives the cell membrane a fluid motion. The cell membrane is
embedded with many different proteins and other substances that allow some
selective materials to enter and leave the cell. The many different substances that
are embedded in the cell membrane give it a look similar to a mosaic in the art world
which uses pieces of tile to form a picture or design.
The phospholipids have a polar, hydrophilic (water attracting) head and two
nonpolar, hydrophobic (water repelling) tails. Phospholipids can move laterally and
allow water and other small molecules to pass through into or out of the cell. Since
the cell membrane is mostly made of lipids, only lipid soluble substances such as
oxygen and carbon dioxide can pass through in this way. Other substances that are
water soluble need to pass through openings created by different kinds of proteins
which are embedded in the membrane. Water soluble substances include molecules
like glucose, amino acids, ions and water.
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A concentration gradient is a difference in concentration between the fluid or
solution outside a cell and the concentration within the cell. When the movement of
molecules does not require energy the molecules are moving down the concentration
gradient (from a higher concentration to a lower concentration). This is known as
simple diffusion. The special term for the diffusion of water is osmosis.
Membrane proteins that make up the mosaic of the membrane are very
important. Some proteins are attached to the surfaces of the cell membrane. These
peripheral proteins are located on both the interior surface and the exterior surface
of the cell membrane. The proteins that are embedded in the lipid bilayer are called
integral proteins. Because the cell membrane is selectively permeable, cells must
have mechanisms for transporting molecules through the lipid bilayer. Membrane
proteins play an important role in this process. For example, some integral proteins
form channels or pores through which certain substances can pass. Other proteins
bind to a substance on one side of the membrane and carry it to the other side of the
membrane. These proteins are called transport proteins.
Proteins form pores or channels in the cell membrane which allows water,
which is not lipid soluble, to move freely across the cell membrane from an area of
greater concentration to an area of lesser concentration.
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Large molecules like glucose or other carbohydrates us transport proteins with
carbohydrate chains to help move across cell membranes. The carbohydrate chains
act like ID cards to help cell recognize certain molecules. Because the large
molecules are moving down the concentration gradient and do not require energy, it
is still a type of diffusion, but with the help of a protein. This process is called
facilitated diffusion.
BEGIN WORKING HERE!!!
LABEL THE FOLLOWING:
What letter of the diagram of the phospholipid bilayer shows the following?
Heads of the lipid molecules ______
Tails of the lipid molecules _______
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Proteins ____, _____, ______
Carbohydrate Chains _______
Questions:
1. Explain why the cell membrane is called a fluid mosaic.
2. The phospholipids have a polar, ___________ head and two nonpolar
_____________ tails.
3. Define hydrophilic - _______________________________________________
4. Define hydrophobic - ______________________________________________
5. Since the cell membrane is mostly lipids, only lipid soluble substances such as
_______________ and _______________ can pass through.
6. Water soluble substances need to pass through openings created by different
kinds of _________________ which are embedded in the membrane.
7. Give examples of water soluble substances: ________________, _______
_________, ___________, and water.
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8. What is a concentration gradient?
9. When molecules move from a higher concentration to a lower concentration, it is
known as simple __________________.
10.
The diffusion of water is called ___________________.
11.
Describe the function of a transport protein.
12.
What type of molecules use transport proteins?
13. Carbohydrate chains act like ______ cards to help cells recognize certain
_____________________.
14.
What is facilitated diffusion?
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