Model 2 - Selectively Permeable Cell Membrane and Simple Diffusion Extracellular Fluid Wwwwww Cytoplasmic Fluid Extracellular Fluid www Cytoplasmic Fluid www w wwwwww www www.x www. www. www www www. ACTE Omw ww ww Type lions Type 2 molecules (glucose) Extracellular Fluid Wwwwwww Cytoplasmic Fluid Extracellular Fluid ww Cytoplasmic Fluid d wwwx w mo AM 8 MO m un www m 8 www www.x www. Summ Type 3 Urea molecules upe 4 oxygen molecules The four diagrams in Model 2 illustrate movement of four types of substances (see the table in Model 1 - the symbols in this model correspond with those from the previous model) across a phospholipid bilayer (extracellular fluid on left and cytoplasmic fluid on right). of 3. Label each diagram in Model 2 with the ion or molecule type (i.e., large/small, polar/nonpolar/charged) based on the information (including the symbols) in Model 1. 4. Assume the substances in Model 2 were on only one side of the membrane to start. The diagrams illustrate what would happen after some time has passed. a. Which substances appear to be completely blocked by the membrane? have completely blocked type lons b. Which substances appear to be able to pass freely through the membrane? The molecular oxygen molecules are able to pass freely. c. Which substances appear to pass through the membrane with some difficulty? Urea + glucose d. Urea appears to pass through the membrane more easily than glucose. What characteristic of urea might help explain this observation? bon anot of 115 compared to glucose which makes potova urea is small easier to pass through the it through the membrane 6 Diffusion is the process of molecules traveling across a membrane barrier from a location of high concentration to a location of low concentration ("down their concentration gradient"). 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 due to the polarity of the molecules themselves and their size. No energy is needed during simple diffusion, so it is considered a type of passive transport. This process is illustrated in Model 2 for several types of molecules. Does the above description match with what we've discussed in lecture? 2 CD Model 3- Osmosis Below are three "cells" that are in different aqueous salt solutions (the salt concentration in the surrounding solution is labeled below each cell). Within each cell, the salt concentration is ~0.9% NaCl. OIOIO 0% NaCl 0.9% NaCl 5% NaCl 5. What is an "aqueous" solution? 6. If the salt ions and membrane behave the same way as illustrated in Model 2 (meaning that these ions cannot freely cross the membrane), is there any other molecule in this aqueous salt solution that can cross the membrane? 7. If water could move across the membrane of each of the cells above, then in which direction would you see net movement of water with respect to each cell? Add arrows to Model 3 to indicate the net direction of water movement in each scenario. Osmosis is the process by which a solvent (water) diffuses down its own gradient. If there is a change in the amount of water in a cell, that has a direct effect on the volume, shape, and viability of a cell. 8. A hypotonic solution is one in which the solute concentration is lower (hypo-) compared to that within the cell. Which of the three solutions in Model 3 would you describe as hypotonic? 9. It is dangerous for an animal cell to be placed into a hypotonic solution. Why do you think this is so? What could happen to an animal cell in a hypotonic solution, based on your response to #7?