When answering these questions use the "Chapter 8 Lecture" or simply read sections of Chapter 8 in your textbook that correspond to the question. The book is very good on this material. Remember to refer to the online CD-ROM and the various animations on the internet that are included as links in the print lecture or in the "Web Resources" section of this unit. Using these resources will increase your understanding of this material since these are processes that can best be learned through animation.

1. One of the main ways molecules move across biological membranes is by passive transport.
a. The driving force behind passive transport is diffusion. Explain diffusion. What is it? Why does it happen? How does it work?
b. Osmosis is a special case of passive transport. Explain what it is, how it works, and why it works. Be sure to include in your answer a discussion of the terms hypertonic, isotonic, and hypotonic.
c. Animal and plant cells use osmosis to respond to different aqueous environments. Discuss the various responses to being placed in hypertonic, isotonic, and hypotonic solutions (see figure 8.11). Include an illustration.

2. a. A special form of passive transport is facilitated diffusion. Explain what this process is and how it works. Why is it considered “passive”?
b. What is active transport? Explain the process and how it works. Why is it called “active”? The sodium-potassium pump is an example of this process. Explain this system.
c. Briefly summarize the difference between passive transport and active transport. Draw an illustration of this similar to that which is shown in figure 8.15.

3. The current model of the cell membrane, or plasma membrane, is called the fluid mosaic model. Explain this model in detail. What kinds of molecules make up the membrane? Be sure to discuss the significance and biochemistry of the lipid bilayer including the importance of hydrophobic and hydrophilic interactions. Go back to page 67 in the book, read the text, and then and look at figures 5.12 & 5.13 as a refresher. Explain how saturated tails, unsaturated tails, and cholesterol function in the membrane. What is meant by “fluid”? What makes the membrane more or less “fluid”? What is meant by “mosaic”? Be sure to discuss the significance of both integral proteins and peripheral proteins- what are they and how do they function in the membrane in general? Describe the role and function of membrane carbohydrates. Be sure to discuss the meaning of the term oligosaccharide. Include a labeled illustration that shows all these different components.

4. A cell membrane is said to be selectively permeable. What is meant by this?
a. The lipid bilayer accounts for part of this selective permeability. Discuss the molecules that move through the membrane and those that don’t move through the membrane due to its lipid bilayer nature. Explain how the lipid bilayer contributes to this selective permeability.
b. Transport proteins account for the other part of this selective permeability. Discuss how these transport proteins contribute to the selective movement of substances across the membrane. Give specific examples of this.