1 .Conversion of substrate to product can occur spontaneously, but this process is slow, not fast enough to sustain life. Reactions mediated by enzymes are much faster, and involve the “Lock-and-Key” model of how shapes of specific enzymes fit with shapes of specific substrates. After fitting the shapes together, the next step is to lower the activation energy of the reaction. Describe how the enzyme can treat the substrate in order to do this.

2. Lactate (lactic acid) is converted to pyruvate by an enzyme called lactate dehydrogenase. Certain plants produce a molecule (let’s call it Inhibitor 1) that inhibits activity of lactate dehydrogenase. When cows eat these plants, Inhibitor 1 is concentrated in their milk. If humans drink milk from these cows they become sick with abdominal pain and vomiting. If these sick people engage in vigorous exercise, their symptoms become worse. Explain why this happens.

3 Lions are obligate carnivores, i.e., they do not eat plants. Do you think a case can be made that the existence of lions depends on the vegetation of their habitat? Describe the reason for the answer you chose.