File
Name: ____________________________________________________________ Date: _______________Period: _____
Standard: MC.2.B.4 Relate the function of the plasma (cell) membrane to its structure.
Bell Ringer: ________________________________________________________________________________________
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Cell Boundaries
Travelling to other countries require a lot of planning. First you must know your destination, and be prepared to cross country borders. Borders separate one country from another. A cell membrane is like a border made of a thin,
flexible barrier that separates the cell from its surroundings. So why do cells need cell membranes? Because cell membranes control what enters and leaves the cell, it provides protection and support for the cell.
Cell (plasma) membranes are made of a double-layered sheet of lipids called the lipid bilayer. These bilayers, along with cholesterol molecules, give the cell a strong, yet flexible structure. Within the lipid bilayer are embedded
proteins that make up pumps and channels that help move materials across the membrane of one cell to another.
Some of the proteins have a carbohydrate attached to it. The carbohydrate acts as a chemical identification card, like a visa on a passport that allows cells to identify one another.
Cell Walls
Some cells also produce a strong supporting layer around the cell membrane known as the cell wall. Cell walls are present in plants, algae, fungi, and many prokaryotes. Most cell walls are made from fibers of carbohydrates and
proteins. Plant cell walls are mostly made of cellulose, a tough carbohydrate fiber that makes up wood, and paper.
The main function of the cell wall is to provide support and protection for the cell.
Cell Wall
Cell Membrane
CYTOPLASM
(inside the cell)
Lipid Bilayer Membrane Model and Soap Bubble mini lab
Make a bilayer using the model parts:
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Each group gets four lipid molecules.
1) Color the hydrophilic heads one color and the hydrophobic tails another.
2) Place a protein molecule in the bilayer and label it.
3) Label the outside and inside of the cell.
Each phospholipids molecule has a polar (hydrophilic) head and two non-polar (hydrophobic) tails. The hydrophobic tails of the two layers repel water and are attracted to each other. They form the inside of the membrane bilayer “sandwich” while the polar heads are on the outside closest to the water
Procedure: Obtain a soap bubble on your soap bubble wand and make observations.
Soap bubbles are bilayers very similar to lipids membranes, so they can be used to investigate some of the properties of the cell membrane. The soap bubble bilayer is made of molecules with a hydrophilic head and a hydrophobic tail, except that the surrounding medium (air) is non-polar, so the tails of the bilayer face outward and the polar heads form the inside.
1. CAN YOU SEE THE SOAP IN MOTION?
Fluidity: The theory of the structure of the cell membrane is called the Fluid Mosaic Model. This means that the membrane is made of a pattern of many small molecules that are moving around and shifting position.
2. IS YOUR BUBBLE RIGID OR FLEXIBLE?
Flexibility: A lipid bilayer is a fluid arrangement within which the molecules can move freely through the plane of the bilayer. They can reorganize themselves into almost any shape without losing the contacts that satisfy their mutual attraction. The soap bilayer is actually less flexible than a cell membrane because a cell membrane is supported on both sides, one side by the cytoplasm and the other by lymph or other tissue fluids. So, whatever you are doing to the soap film, plus more, can be done to cell membranes without breaking them.
3. MAKE A SECOND BUBBLE AND TRY TO UNITE THEM.
Self-Sealing: Remember that the membrane is not a solid. It is made of two layers of many molecules attracted to each other.
Name: ___________________________________________________________ Date: _______________ Period: ______
Hydrophilic Head
Hydrophobic
Phospholipid molecule
Tail
Soap molecule
Post Lab Questions
Hydrophilic heads on the surface
Phospholipid Bilayer
Hydrophobic tails on the surface
Soap Bilayer
1.
What four things compose a cell membrane?
2.
How are soap molecules and cell membranes alike?
3.
How are they different?
4.
What does hydrophilic and hydrophobic mean?
5.
How many layers of phospholipids do cell membranes have?
