OpenStax Biology 2e Instructor Answer Guide
Biology 2e
Unit 2: The Cell
Chapter 7: Cellular Respiration
Visual Connection Questions
1. Dinitrophenol (DNP) is an “uncoupler” that makes the inner mitochondrial membrane “leaky”
to protons. It was used until 1938 as a weight-loss drug. What effect would you expect DNP to
have on the change in pH across the inner mitochondrial membrane? Why do you think this
might be an effective weight-loss drug?
After DNP poisoning, the electron transport chain can no longer form a proton gradient, and
ATP synthase can no longer make ATP. DNP is an effective diet drug because it uncouples ATP
synthesis; in other words, after taking it, a person obtains less energy out of the food he or she
eats. Interestingly, one of the worst side effects of this drug is hyperthermia, or overheating of
the body. Since ATP cannot be formed, the energy from electron transport is lost as heat.
, OpenStax Biology 2e Instructor Answer Guide
2. Cyanide inhibits cytochrome c oxidase, a component of the electron transport chain. If
cyanide poisoning occurs, would you expect the pH of the intermembrane space to increase or
decrease? What effect would cyanide have on ATP synthesis?
After cyanide poisoning, the electron transport chain can no longer pump electrons into the
intermembrane space. The pH of the intermembrane space would increase, the pH gradient
would decrease, and ATP synthesis would stop.
3. Tremetol, a metabolic poison found in the white snake root plant, prevents the metabolism
of lactate. When cows eat this plant, it is concentrated in the milk they produce. Humans who
consume the milk become ill. Symptoms of this disease, which include vomiting, abdominal
pain, and tremors, become worse after exercise. Why do you think this is the case?
The illness is caused by lactate accumulation. Lactate levels rise after exercise, making the
symptoms worse. Milk sickness is rare today, but was common in the Midwestern United States
in the early 1800s.
Biology 2e
Unit 2: The Cell
Chapter 7: Cellular Respiration
Visual Connection Questions
1. Dinitrophenol (DNP) is an “uncoupler” that makes the inner mitochondrial membrane “leaky”
to protons. It was used until 1938 as a weight-loss drug. What effect would you expect DNP to
have on the change in pH across the inner mitochondrial membrane? Why do you think this
might be an effective weight-loss drug?
After DNP poisoning, the electron transport chain can no longer form a proton gradient, and
ATP synthase can no longer make ATP. DNP is an effective diet drug because it uncouples ATP
synthesis; in other words, after taking it, a person obtains less energy out of the food he or she
eats. Interestingly, one of the worst side effects of this drug is hyperthermia, or overheating of
the body. Since ATP cannot be formed, the energy from electron transport is lost as heat.
, OpenStax Biology 2e Instructor Answer Guide
2. Cyanide inhibits cytochrome c oxidase, a component of the electron transport chain. If
cyanide poisoning occurs, would you expect the pH of the intermembrane space to increase or
decrease? What effect would cyanide have on ATP synthesis?
After cyanide poisoning, the electron transport chain can no longer pump electrons into the
intermembrane space. The pH of the intermembrane space would increase, the pH gradient
would decrease, and ATP synthesis would stop.
3. Tremetol, a metabolic poison found in the white snake root plant, prevents the metabolism
of lactate. When cows eat this plant, it is concentrated in the milk they produce. Humans who
consume the milk become ill. Symptoms of this disease, which include vomiting, abdominal
pain, and tremors, become worse after exercise. Why do you think this is the case?
The illness is caused by lactate accumulation. Lactate levels rise after exercise, making the
symptoms worse. Milk sickness is rare today, but was common in the Midwestern United States
in the early 1800s.
