Focus Questions: Membrane Transport 1. What is the structure of membrane phospholipids and how do we know this? Is the membrane permeable to any substance? What kinds of molecules are able to pass through the membrane most easily? What kinds of molecules cannot cross the membrane easily? 2. If there is a higher concentration of a small hydrophobic molecule outside the cell than inside, what will happen? Will this result in a higher concentration of this molecule inside the cell? What would happen if the original molecule were hydrophilic? 3. What does it mean to say that the membrane is fluid? Can the cell control the degree of fluidity of the membrane? Does this involve changes in proteins in the membrane, or changes in fatty acid composition? How would a cell respond to an increase in temperature to maintain the same membrane fluidity? 4. How are molecules that cannot diffuse across the membrane transported across the membrane?
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