Download cell membrane info ws - Hicksville Public Schools

Cell Membrane Information Worksheet
- Dr. Lamia
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.
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.
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.
*Color the diagram of the phospholipid bilayer below as follows:
Heads of the lipid molecules – red
Tails of the lipid molecules – blue
Proteins (B, C, and H) - yellow
Carbohydrate Chains - orange
Questions:
1. Explain why the cell membrane is called a fluid mosaic.
The phospholipids that make up the membrane lie next to each other but are not connected.
This gives the cell membrane a fluid motion. Many substances are embedded in the cell
membrane giving it a mosaic look.
hydrophilic
hydrophobic tails.
2. The phospholipids have a polar, ___________head
and two nonpolar ____________
Water attracting
3. Define hydrophilic - _______________________________________________
Water repelling
4. Define hydrophobic - ______________________________________________
5. Since the cell membrane is mostly lipids, only lipid soluble substances such as
CO2
H2O
_______________
and _______________
can pass through.
6. Water soluble substances need to pass through openings created by different
proteins
kinds of _____________
which are embedded in the membrane.
glucose
Amino acids
7. Give examples of water soluble substances: ___________,
____________,
ions and water.
_______,
8. What is a concentration gradient?
A difference in concentration between the fluid or solution outside a cell and the
concentration within the cell.
9. When molecules move from a higher concentration to a lower concentration, it
diffusion
is known as simple ___________.
osmosis
10. The diffusion of water is called __________.
11. Describe the function of a transport protein.
Proteins that bind to a substance on one side of the membrane and carry it to the
other side of the membrane.
_______________________________________________________________
Glucose & other carbohydrates
12. What type of molecules use transport proteins? __________________________
ID
13. Carbohydrate chains act like ______
cards to help cells recognize certain
molecules
_____________________.
14. What is facilitated diffusion?
When large molecules are moving down the concentration gradient and do
not require energy, but move with the help of a transport protein.