2. Which is likely to be a nonpolar solvent? A. B. B shows a carboxyl group, while A is only carbons and hydrogens.

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1 An organic chemistry lab uses thin layer chromatography to determine the relative polarity of different molecules. The molecules are added to the bottom of a glass plate covered with polar silicone gel and the plate is placed in a beaker of ethyl acetate, a nonpolar solvent. The solvent travels up the plate, carrying the molecules with it. More polar molecules are attracted to the silicone and don t travel as far. 1. Molecules with which functional groups will be more attracted to the silicon gel on the plate? A. Hydroxyl B. Sulfhydryl C. Methyl Only hydroxyl groups are strongly polar. 2. Which is likely to be a nonpolar solvent? A. B. B shows a carboxyl group, while A is only carbons and hydrogens. Three pain medications (aspirin, caffeine, Anacin brand pain reliever) were added to the starting line of the plate and the plate was placed in the solvent. After the solvent was allowed to travel 5 cm up the plate, the plate was removed and dried and the locations of the molecules marked, as shown. 3. Which of the following is true? A. Aspirin is more polar because it traveled further B. Caffeine is more polar because it was more attracted to the solvent C. Aspirin is more polar because it was more attracted to the silicone D. Caffeine is more polar because it did not travel as far Silicone is polar, so more polar molecules will be attracted faster. Aspirin did not move as far as caffeine, so aspirin is more polar. 4. Which hypothesis is the most likely reason for this experiment? A. Aspirin is a more effective pain reliever than caffeine or Anacin B. Anacin is a combination of more than one pain reliever C. Aspirin is a larger molecule than caffeine or Anacin D. Ethyl acetate is more nonpolar than benzene

2 Name: While any of the above may be true or may be hypotheses for an experiment, this experiment is suited for separating molecular components by polarity rather than size. 5. Which pain reliever is more likely to diffuse across plasma membranes in the brain? A. Aspirin, because it is more polar B. Caffeine, because it is more polar C. Aspirin, because it is more nonpolar D. Caffeine, because it is more nonpolar You must be able to both read the chromatography results and remember that nonpolar molecules diffuse more easily across a plasma membrane. 6. This molecule is found in many plasma membranes. What molecule is it most similar to? A. Phospholipid B. Steroid C. Protein D. Cholesterol This is a sphingolipid, used in the FRAP experiment below. Proteins are shaped differently, and while steroids, including cholesterol can have a long tail, their tail usually contains rings. In experiments called fluorescence recovery after photobleaching or FRAP, a fluorescent tag is added to the polar head of a lipid. This makes the entire cell glow under fluorescent light. A laser is used to bleach (remove color) from one small area of the membrane. The time required for lipids with non-bleached tags to diffuse into the bleached area is then measured. A diagram is shown. 7. Which membrane process is this experimental design best suited to measure? A. Ability of membrane lipids to move laterally B. Transport of polar molecules across the plasma membrane C. Ability of cell to manufacture fluorescent tags D. Ability of cell to manufacture membrane lipids This technique measures how quickly the cell recovers from a perturbation to the plasma membrane. In an experiment to test the use of a new microscope in FRAPping, researchers compared the recovery curve of a cell with and without the addition of cyclodextrin (cdx), a drug that affects membrane cholesterol. Here are their results:

3 8. Which treatment recovered its fluorescence faster, the control or the cyclodextrin? A. The control because it approached 100% fluorescence faster B. The cyclodextrin because it approached 100% fluorescence faster C. The control because the recovery curve is shifted to the right D. The cyclodextrin because the recovery curve is shifted to the right. 100% of recovered fluorescence is set at 1 on the Y axis. The cdx-treated membrane recovers more quickly, with the curve shifted to the left. 9. What is the likely effect of cyclodextrin (assume 25 o C)? A. Decreases the amount of cholesterol, reducing membrane fluidity B. Increases the amount of cholesterol, reducing membrane fluidity C. Decreases the amount of cholesterol, increasing membrane fluidity D. Increases the amount of cholesterol, increasing membrane fluidity You must recognize that cdx causes increased fluidity, and remember that reducing cholesterol increases fluidity. Researchers invited over 5,000 Americans to be part of a study that measured their reaction times ability to quickly press a button when an image appears on a computer screen. When they checked on the subjects 15 years later, they found that people with slower reaction times were more likely to have died. 10. If roughly 500 subjects were dead after 15 years, what percentage of the original group died? A. 0.1% B. 1% C. 5% D. 10% 500/5000 = 10% 11. The researchers listed the hazard ratio of slow-reaction-timers as 1.25, indicating their chance of dying was 1.25 times higher than those with normal reaction times. This is the same as: A. A 0.25% increase B. A 2.5% increase C. A 25% increase D. A 125% increase 1.25 times higher is the same as a 25% increase. This figure is from the article. The participants were divided into three groups: those with slowest reaction times, those with medium reaction times, and those with fast reaction times.

4 Name: 12. What correlates with a slow reaction time? A. Being male, not graduating high school B. Drinking heavily, high poverty C. Exercising little and being an ethnic minority To answer this, you needed to find characteristics that were high in the Slow group proceeds to lower in the Fast group. Males tend to have faster reaction times, drinking does not correlate with reaction time. 13. The breaking of an ionic bond: A. Often occurs in the presence of water B. Is a hydrolysis reaction C. Dissociates a glucose molecule into carbons, hydrogens and oxygens Ionic bonds are common in salts, which dissociate in water. They are not found in a glucose molecule, and the reaction is not called hydrolysis 14. Which is true of actin but not myosin? A. Subunits added and subtracted from plus end B. Minus ends are near the plasma membrane C. Are associated with a motor protein This question was given to everyone because myosin should have read microtubules 15. If microtubule subunits were unable to bind to each other, which would be affected? A. Movement of cytoplasm and pseudopodia B. Beating of cilia C. Myosin pulling Z-disks toward each other Cytoplasmic streaming and muscle contraction are both controlled by actin. 16. A drug suddenly blocks the sodium-potassium pumps in a cell membrane. This would cause: A. An increase in ATP use B. An increase in potassium ions entering the cell C. The inside of the cell to become more negative D. An increase in intracellular sodium

5 If the pump stopped working, less sodium would leave the cell and less potassium would enter. This would reduce the charge difference across the cell membrane and reduce ATP use. 17. A common risk for runners new to marathons is drinking too much water. This causes hyponatremia, or low sodium levels in the blood. Why would this cause headache, disorientation and sometimes death? A. The cytoplasm in the brain cells has a lower water concentration B. The blood is hypertonic to brain cells C. Water would flow from the blood to the brain D. Cells in the brain would attempt to pump sodium and potassium into the blood If the blood is more dilute from drinking more water, it will be hypotonic to brain cells. Cells cannot pump both sodium and potassium into the blood, plus they need to keep the cell concentration stable. The effect is water flows into the cells, causing swelling and trauma to the brain. 18. Unlike simple diffusion, facilitated diffusion: A. Moves charged molecules across the membrane B. Does not require the use of a transporter C. Moves substances from high to low concentration D. Requires no energy Both types of diffusion move substances from high to low concentration and neither requires energy. Facilitated diffusion does require transporters and can move charged molecules. 19. The figure at the right is an illustration of a U-tube apparatus. The membrane (dashed line) separating both sides is permeable to water, but not permeable to the solute particles shown. On the left side there are 21 particles in 5 ml of water and on the right side there are 9 particles in 5 ml of water. After allowing the U-tube to come to equilibrium, what do you expect to see? A. There will be 15 particles on each side B. There will be 7 ml of water on the left C. There will be 6 ml of water on the right D. The right side will remain hypertonic The solute particles cannot move, so water will move to the left. The left will remain hypertonic compared to the right. 20. What happens when you eat a Twinkie (a small cake)? A. Molecules in the Twinkie are broken down by dehydration reactions that use water B. Molecules in the Twinkie are broken down by hydrolysis reactions that use water C. Molecules in the Twinkie are broken down by dehydration reactions that release water D. Molecules in the Twinkie are broken down by hydrolysis reactions that release water Comprehension question: macromolecules are broken down by hydrolysis reactions and these require water.