Texts: 6. Assume the substances in Model 2 were only on one side of the membrane to start. The diagrams illustrate what would happen after some time has passed. Which substances in Model 2 appear to be completely blocked by the membrane? b. Which substances in Model 2 appear to be able to pass freely through the membrane? Which substances in Model 2 appear to pass through the membrane with some difficulty? Urea appears to pass through the membrane more easily than glucose. What characteristic of urea might help explain this observation? 7. The majority of the membrane is made of nonpolar hydrocarbon chains. Use the diagrams in Model 2 and the table in Model 1 to explain the permeability of the membrane for each of the four types of substances in Model 1. Hint: Like dissolves like. Type 1 Ions: Type 2 Molecules (Large, polar biomolecules): Type 3 Molecules (Small, polar molecules) Type 4 Molecules (Small, nonpolar molecules) Read This! Diffusion is the process of molecules traveling through a membrane barrier from a location of high concentration to a location of low concentration. The driving force for this process is simply the natural movement of the molecules in random directions. Whether the molecules are allowed to cross or not is only due to the polarity of the molecules themselves and their size. No energy is needed, which is why diffusion is considered a type of passive transport. This process is illustrated in Model 2 for several types of molecules. Membrane Function

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