Correct answers are in bold, but be sure to read why the other answers are not correct.

1. Where does carbon dioxide-rich blood from the capillaries in the gut go?
   1. lungs → right side of the heart → left side of the heart
      You are partly right. Before entering the lungs, red blood cells carrying carbon dioxide in the veins must first return to the right side of the heart. Oxygenated blood from the lungs returns to the left side of the heart for distribution to the rest of the body, including the brain.
   2. right side of the heart → the lungs → left side of the heart
      Terrific! Red blood cells carrying carbon dioxide in the veins must first return to the right side of the heart. The right side of the heart pumps the blood into the lungs where carbon dioxide is exchanged for oxygen in the capillaries. Oxygenated blood from the lungs returns to the left side of the heart for distribution to the rest of the body, including the brain.
   3. left side of the heart → the lungs → right side of the heart
      Sorry, you got it backwards. Red blood cells carrying carbon dioxide in the veins must first return to the right side of the heart. The right side of the heart pumps the blood into the lungs where carbon dioxide is exchanged for oxygen in the capillaries. Oxygenated blood from the lungs returns to the left side of the heart for distribution to the rest of the body, including the brain.
   4. lungs → left side of the heart → right side of the heart
      Sorry, that is incorrect. Before entering the lungs, red blood cells carrying carbon dioxide in the veins must first return to the rightside of the heart. Oxygenated blood from the lungs returns to the left side of the heart for distribution to the rest of the body, including the brain.
2. Ethanol is more volatile than water because it has:
   1. fewer hydrogen bonds
      You are right! The oxygen atom in ethanol has only 3 bonds available for hydrogen bonding. Individual water molecules may be held together with as many as 4 hydrogen bonds. Fewer hydrogen bonds to break makes it easier to vaporize.
   2. more hydrogen bonds
      Sorry, that is incorrect. The oxygen atom in ethanol has only 3 bonds available for hydrogen bonding. Individual water molecules may be held together with as many as 4 hydrogen bonds.
   3. carbon atoms
      Sorry, try again. Although ethanol does have 2 carbon atoms, they do not participate in hydrogen bonding.
   4. nitrogen atoms
      Sorry, try again. Nitrogen atoms can participate in hydrogen bonding, however neither ethanol nor water contain a nitrogen atom.
3. Which of the following statements describes ethanol equilibrium between the blood and the alveoli?
   1. The amount of ethanol is the same in the blood relative to the alveoli.
      Sorry, many people get this wrong. In a state of equilibrium, the ratio of the ethanol concentration in the blood relative to the alveoli achieves a constant value.
   2. The concentration of ethanol is the same in the blood relative to the alveoli.
      Sorry, many people get this wrong. In a state of equilibrium, the ratio of the ethanol concentration in the blood relative to the alveoli achieves a constant value.
   3. Ethanol stops moving between the blood and the alveoli.
      Sorry, many people get this wrong. In a state of equilibrium, ethanol molecules still move back and forth, but there is no net flow. The ratio of the ethanol concentration in the blood relative to the alveoli achieves a constant value.
   4. There is no net flow of ethanol between the blood and the alveoli.
      Yes, you are correct! In a state of equilibrium, the ratio of the ethanol concentration in the blood relative to the alveoli achieves a constant value. Ethanol molecules still move back and forth, but there is no net flow.
4. No energy is required for the passive diffusion of ethanol out of the gut and into the bloodstream. If energy is not required, then what drives the diffusion process?
   1. ethanol’s small molecular size
      Sorry, not quite. The small molecular size makes it easy for ethanol to cross a membrane, but it is not a force that drives it across.
   2. proton pumps
      Sorry, try again. Proton pumps require energy to move molecules across a membrane.
   3. the higher concentration of ethanol in the bloodstream relative to the gut
      Sorry, you have it backwards. Molecules passively diffuse across a biological membrane from an area of high concentration (in the gut) to an area of low concentration (in the blood).
   4. the higher concentration of ethanol in the gut relative to the bloodstream
      Yes, you got it right! Molecules passively diffuse across a biological membrane from an area of high concentration (in the gut) to an area of low concentration (in the blood).
5. When hydrogen is burned it combines with oxygen to produce water molecules. Which describes the state of each atom?
   1. Hydrogen is oxidized, Oxygen is reduced
      Correct! Hydrogen is an electron acceptor and gains an oxygen (is oxidized), while oxygen gains a hydrogen (is reduced).
   2. Oxygen is oxidized, Hydrogen is reduced
      No, you got it backwards. Hydrogen is an electron acceptor and gains an oxygen (is oxidized), while oxygen gains a hydrogen (is reduced).
   3. Both are oxidized
      Sorry, you are incorrect. Hydrogen is an electron acceptor and gains an oxygen (is oxidized), while oxygen gains a hydrogen (is reduced).
   4. Both are reduced
      Sorry, you are incorrect. Hydrogen is an electron acceptor and gains an oxygen (is oxidized), while oxygen gains a hydrogen (is reduced).