The+Cell+Membane+-+8th

**The Cell Membrane**
 * Activity One **

**If you study the diagram above, you will notice that the cell (plasma) membrane is not composed of only one molecule. In fact, the proteins, lipids, phosphates, carbohydrates and other molecules that comprise the cell membrane give it its unique character and abilities. Let's look at these various molecules:**
 * **Integral proteins. You can see that these proteins have an opening into and out of the cell. What do you think these proteins might do?**
 * **Peripheral proteins. These are proteins that are only embedded in the surface of the membrane. Let your fingers do the googling and find out what these proteins do.**
 * **Oligosaccharides. These are branched sugars that extend from the outside top of the membrane. What is their purpose?**
 * **Cholesterols. Ooooh, ugly bad word. We think of cholesterols as dangerous things that have to be eliminated, but they must have a purpose. Find out what it is.**
 * **The phospholipid bilayer. The membrane itself is composed of molecules called phospholipids: notice that in the diagram they have a round phosphate head and two little lipid tails that extend into the middle of the membrane. Since the membrane is a bilayer, it has two layers of phospholipids; you can see that the tails point toward each other and the phosphate heads are on the outside. Each phospholipid molecule is in constant motion. This allows the free movement of certain substances across the membrane. Name three substances that pass freely across the membrane.**


 * Activity Two **
 * Now let's take a closer look at the phospholipid bilayer itself.**
 * Remember when we were learning the organelles of the cell? We said the membrane was very selective about what could enter and learve the cell. The protein channels (in red above) help to regulate the traffic across the membrane. Why do you think this is so important? **

**Think about what these two words mean individually and collectively. Write down your definition of passive transport.** Now check this [|glossary] for its actual meaning. How close was your definition to the scientific one? By the way, remember this glossary link; you will use it again.
 * Activity Three **
 * Passive Transport **


 * We will be studying three types of passive transport:** ** diffusion, osmosis and facilitated diffusion. **
 * 1) ** Diffusion is the movement of particles from an area of high concentration to an area of low concentration. It can take place through a variety of media: through water, through air or across a phospholipid bilayer.**
 * 2) **Click on [|this link] to see a demonstration of diffusion through air.**
 * 3) **Which of the following scenarios are examples of diffusion?**
 * **On Saturday morning, you smell bacon frying in the downstairs kitchen.**
 * **Kool-Aid mix being stirred into a pitcher of water.**
 * **Food coloring added to a glass of water.**
 * **The smell of ozone just before a summer rain.**
 * **The odor of perfume lingering in the room after the woman has left.**

View this [|animation] of osmosis and complete the quiz.