chapter 9

• To perform their many tasks, living cells require energy from outside sources.
• Energy enters most ecosystems as sunlight and leaves as heat.
• Photosynthesis generates oxygen and organic molecules that the mitochondria of eukaryotes use as fuel for cellular respiration.
• Cells harvest the chemical energy stored in organic molecules and use it to regenerate ATP, the molecule that drives most cellular work.
• Respiration has three key pathways: glycolysis, the citric acid cycle, and oxidative phosphorylation.

Figure 9.3 shows the electron transport chain. Which of the following is the combination of substances that is initially added to the chain?

A) oxygen, carbon dioxide, and water

B) NAD⁺, FAD, and electrons

C) NADH, FADH₂, and protons

D) NADH, FADH₂, and O₂

E) oxygen and protons

Which of the following most accurately describes what is happening along the electron transport chain in Figure 9.3?

A) Chemiosmosis is coupled with electron transfer.

B) Each electron carrier alternates between being reduced and being oxidized.

D) Energy of the electrons increases at each step.

E) Molecules in the chain give up some of their potential energy.

Which of the protein complexes labeled with Roman numerals in Figure 9.3 will transfer electrons to O₂?

A) complex I

B) complex II

C) complex III

D) complex IV

E) All of the complexes can transfer electrons to O₂.