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Page 1: Introduction Page 2: 1. Hydrocarbons are referred to as organic molecules with a "backbone." Take a snapshot of the hydrocarbon you created and drag the snapshot into the box below. Use the arrow tool to point to the carbon backbone. 1. Why do you think the charge arranges itself for ketene in this way? The negatively charged electrons are attracted to the oxygen atom. Since the oxygen end of the molecule steals more of the negative charge, the remainder of the molecule is left partially positive. 2. Which compound boils first? (a) 3. How does the presence of the oxygen atoms in the molecule account for the difference? The oxygen atoms make ketene a polar molecule increasing the attraction between partial positive and partial negative ends of molecules. Therefore, it requires more energy, in the form of heat, to break the molecules apart and cause the liquid to boil. Page 4: 1. Which of the following are true? (a) (b) (c) 2. Take a snapshot of a lipid that is fully dissolved (evenly spread in the solvent). Sample snapshot: Lipids evenly spread in the solvent. Sample Snapshot: Hydrocarbon molecule created. 2. How many bonds does every carbon atom have? Four (4) Page 3: 3. Hydrophilic means something is attracted to water and hydrophobic means something is excluded from water because water is more attracted to other water molecules than to it. Are the lipids hydrophobic or hydrophilic? Explain your answer. The lipid molecule is hydrophobic. This is apparent because the lipid molecule is not dissolving in water. The water molecules are more attracted to each other than they are to the

fat. This results in the lipid remaining together as a clump. Page 5: 1. What can you tell about the properties of the fatty acid from observing it? Check all that apply. (a) (c) (f) 2. Compare the structure and the polarity of the fatty acid to the hydrocarbon. The hydrocarbon is non-polar (neutral) while the fatty acid is polar. The carboxyl head on the fatty acid has oxygen atoms that will steal negative charge. 3. Explain why the tails are located in the oil and the heads in the water. The tail of the molecule is a long hydrocarbon chain that is hydrophobic. The head is a polar carboxyl group that makes it hydrophilic. So water molecules attract the heads but not the tails. 4. Why are fatty acids compared to the twofaced deity Janus? (c) 5. Take a snapshot of the lipid structure in water. Drag the snapshot into the box below. Sample Snapshot: Fatty acids in oil. 7. Have you ever observed beads of oil on the surface of soup? Explain how this model can help explain the occurrence of those beads. The oil forms clusters on the surface of the soup because they are not soluble in the water-based soup. The fat molecules are excluded from the water. Page 6: 1. Which statement about membrane phospholipids is NOT true? (e) 2. Membranes can keep chemicals inside and outside of the cell. What would happen if a cell membrane breaks? If the cell membrane breaks there would be no regulation of what can enter and leave the cell. Page 7: Sample Snapshot: Fatty acids in water. 6. Take a snapshot of the lipid structure in oil. Drag the snapshot into the box below. 1. How is the lipid molecule different from the sugar molecule? (Check all that apply.) (b) (c) 2. An increase in the ratio of oxygen atoms to hydrogen and carbon... (Check all that are true.) (a) (c) 3. Select a snapshot image that shows benzene molecules do not mix well with water molecules.

When aligned together the function of these molecules can be to act as a building material or protective coating. Link back to Intermolecular Attractions. 2. Long linear polysaccharides make strong fibers because: (d) Page 9: Sample Snapshot: Benzene with Water Molecules 4. Fill in a snapshot image that shows glucose molecules mix better with water molecules. 1. Branched polysaccharides can be more easily separated into individual chains then linear polysaccharides like cellulose. This is explained by: (d) 2. Based on your observations of the polysaccharides in the models, explain why starch is edible and wood is not. Starch, a branched polysaccharide, has many fewer intermolecular attractions because the polymers cannot fit together tightly. It breaks apart as the temperature is increased. Wood's linear nature makes so many more attractions between molecules that is it much stronger, and they do not break apart even at higher temperatures. Page 10: 1. Which substance produces more chemical energy, starch or glycogen, when enzymes work on it? Why? Sample Snapshot: Glucose with Water Molecules 5. Explain how the presence of six OH groups affects the solubility and properties of glucose. The presence of six OH groups makes glucose a polar molecule. The uneven distribution of charge increases its solubility in water, which is also polar. Page 8: 1. How do long chains of parallel cellulose molecules relate to its ability to do its function? Glycogen produces more chemical energy according to the bar graph. Because it is more highly branched, it has more "ends" for the enzymes to attack. 2. Which substance would produce more chemical energy if enzymes could attack in the middle of the chain rather then just at the ends? There would be less of a difference in the chemical energy released if the enzyme could attack anywhere in the molecule. Page 11: 1. In the model to the left, three molecules tagged as "A", "B" and "C" are placed in water. Click the "" button to run the model and observe what happens. Based on your

observation, can you tell which molecule is the most polar? (a) 2. Compare two hydrocarbon chains: one that includes oxygen atoms and one without. How does the presence of oxygen affect the properties of a hydrocarbon chain? (a) 3. What makes cellulose so strong? (a) 4. Describe which lipids are so important to cellular evolution. Why? Scientists believe that the first step in cellular evolution was the emergence of lipids. These lipids are thought to have become more complicated. Then, the lipids formed membranes that created an interior space, separating it from an outside environment. 5. Table sugar and wood are both made of glucose. Why can you serve cubes of sugar with tea, but not cubes of wood (without offending your guests)? The amount of branching in polysaccharides will impact their structure, particularly at different temperatures. Cubes of sugar will dissolve when heated by being placed in hot tea while cubes of wood will maintain their solid structure. This is due to the increased attraction (hydrogen bonding) in wood, which is linear as opposed to sugar, which is branched. 6. Which statement about membrane phospholipids is NOT true? (d)

SAM HOMEWORK QUESTIONS: Lipids and Carbohydrates Directions: After completing the unit, answer the following questions to review. 1. What is the difference between a polar and non-polar molecule? How does this relate to the term electronegativity? 2. What properties impact if a molecule is soluble in specific solvents? 3. What will happen if you try to dissolve a lipid in water? If you change the solvent to oil, instead of water, what will happen to the lipid? Why? 4. Phospholipids form the cell membrane. In the space below, draw how the phospholipids arrange themselves in the cell membrane. Then, explain why this is the case given what you know about the hydrophobic and hydrophilic parts of the molecules. Be sure to label your drawing. 5. Write captions that explain what is happening to the phospholipids in the two pictures seen below. Caption: Caption: 6. How do intermolecular attractions play a role in the behavior of polysaccharides?