Cellular Respiration - AP Biology

1. What role does oxygen play in cellular respiration?

   Final electron acceptor. Receives electrons from ETC, allowing electron flow to continue.

2. Which molecule primarily fuels cellular respiration?

   Glucose. Primary sugar molecule that cells break down for energy production.

3. Where is the electron transport chain located?

   Inner mitochondrial membrane. Embedded in the cristae where proton pumping and ATP synthesis occur.

4. Which electron carrier enters the ETC at a higher energy level: NADH or FADH$_2$?

   NADH. NADH enters at Complex I while FADH$_2$ enters at Complex II.

5. What are the end products of fermentation?

   Lactic acid or ethanol and $CO_2$. Different pathways regenerate NAD⁺ without oxygen for continued glycolysis.

6. Which complex directly reduces $\text{O}_2$ to form water in the ETC?

   Complex IV (cytochrome c oxidase). This complex catalyzes the final electron transfer to oxygen.

7. What process converts pyruvate to acetyl-CoA before the citric acid cycle?

   Pyruvate oxidation (acetyl-CoA formation). Pyruvate is decarboxylated and combined with coenzyme A.

8. What is the primary purpose of cellular respiration in cells?

   To generate ATP by oxidizing organic molecules. Cells break down glucose and other molecules to harvest chemical energy.

9. Identify the second stage of cellular respiration.

   Krebs cycle (Citric Acid Cycle). Acetyl-CoA is oxidized to produce electron carriers and ATP.

10. What is the final electron acceptor in the electron transport chain?

    Oxygen. Oxygen receives electrons at the end of the chain, forming water.

11. What is substrate-level phosphorylation?

    Direct ATP synthesis from a substrate in glycolysis/Krebs cycle. Direct transfer of phosphate from substrate to ADP without electron transport.

12. What happens to pyruvate before entering the Krebs cycle?

    Converted to Acetyl-CoA. Pyruvate oxidation removes one carbon as $CO_2$ to form acetyl-CoA.

13. Which molecule is essential for ATP synthesis in mitochondria?

    ADP. ADP is the acceptor molecule that gets phosphorylated to form ATP.

14. What is the proton-motive force?

    Electrochemical gradient of $\text{H}^+$ across the inner membrane. Concentration and electrical gradients of protons store potential energy.

15. Where does glycolysis occur in the cell?

    Cytoplasm. Glycolysis occurs outside the mitochondria in the cell's main compartment.

16. Which process regenerates NAD⁺ under anaerobic conditions?

    Fermentation. Allows glycolysis to continue when oxygen is unavailable for ETC.

17. What molecule is the final electron acceptor in aerobic respiration?

    Oxygen ($\text{O}_2$). Oxygen accepts electrons at the end of the electron transport chain.

18. Which gas is released during the Krebs cycle?

    Carbon dioxide ($CO_2$). Carbon atoms from acetyl groups are released as waste $CO_2$ gas.

19. What is the approximate ATP yield per FADH$_2$ in many AP Biology contexts?

    About $1.5$ ATP per FADH$_2$. FADH$_2$ bypasses Complex I, generating fewer ATP molecules.

20. What is the effect of an uncoupler on oxidative phosphorylation?

    Disrupts proton gradient, reducing ATP synthesis. Allows protons to leak across membrane, bypassing ATP synthase.

21. What is a typical total ATP yield per glucose for aerobic respiration in eukaryotes?

    About $30$–$32$ ATP per glucose. Modern estimates account for proton leak and transport costs.

22. What is substrate-level phosphorylation?

    ATP made by direct phosphate transfer from a substrate. Direct enzymatic transfer of phosphate group from substrate to ADP.

23. What is the function of ATP synthase?

    Catalyzes the formation of ATP. This enzyme uses proton gradient energy to phosphorylate ADP into ATP.

24. Which reduced electron carrier is produced during glycolysis?

    NADH. NAD$^+$ accepts electrons during glucose oxidation to become NADH.

25. What molecule is glucose converted into during glycolysis?

    Pyruvate. Glucose is split into two 3-carbon pyruvate molecules during glycolysis.

26. How many ATP molecules are produced in total from one glucose molecule?

    Approximately 38 ATP molecules. Maximum theoretical yield from complete glucose oxidation through all stages.

27. Where does glycolysis occur in eukaryotic cells?

    Cytosol. Glycolysis occurs in the cell's cytoplasm, not in organelles.

28. Which mitochondrial membrane must be largely impermeable to $\text{H}^+$ for chemiosmosis to work?

    Inner mitochondrial membrane. Impermeability maintains the proton gradient essential for ATP synthesis.

29. How many carbon atoms are in one pyruvate molecule?

    Three. Pyruvate is a 3-carbon molecule formed when 6-carbon glucose is split.

30. Which type of phosphorylation occurs in glycolysis and the citric acid cycle?

    Substrate-level phosphorylation. Direct phosphate transfer from substrate to ADP without electron transport.

31. Identify the main reason oxygen is required for continued glycolysis in aerobic cells.

    It allows NADH oxidation to regenerate NAD$^+$ via the ETC. NAD$^+$ must be regenerated to continue the glycolytic pathway.

32. What is the net ATP yield from glycolysis per glucose molecule?

    Net 2 ATP. Four ATP are made but two are consumed, yielding net gain of two.

33. Identify the correct statement about NAD$^+$ and NADH in respiration.

    NAD$^+$ is reduced to NADH when it gains electrons (and $\text{H}^+$). NAD$^+$ serves as an electron acceptor during glucose oxidation.

34. Identify the products of one turn of the citric acid cycle per acetyl-CoA.

    3 NADH, 1 FADH$_2$, 1 ATP (or GTP), 2 $\text{CO}_2$. One acetyl-CoA is completely oxidized in each cycle turn.

35. What is the role of Coenzyme A in cellular respiration?

    Transfers acetyl group to the Krebs cycle. Carries acetyl groups from pyruvate oxidation into the Krebs cycle.

36. What is the main purpose of cellular respiration?

    To produce ATP. Converts glucose energy into usable cellular energy currency (ATP).

37. What are the products of lactic acid fermentation from one pyruvate?

    Lactate and NAD$^+$. Pyruvate is reduced while NADH is oxidized to NAD$^+$.

38. How many ATP are produced per glucose in the Krebs cycle?

    2 ATP molecules. Two turns of the cycle produce 2 ATP through substrate-level phosphorylation.

39. Which process produces the majority of ATP in aerobic respiration?

    Oxidative phosphorylation (ETC and chemiosmosis). The electron transport chain and chemiosmosis generate most ATP.

40. Which overall chemical equation summarizes aerobic cellular respiration of one glucose molecule?

    $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP (energy)}$. The complete oxidation of glucose to $\text{CO}_2$ and water with ATP production.

41. Which enzyme complex is inhibited by cyanide in the ETC?

    Cytochrome c oxidase. Cyanide blocks Complex IV, preventing oxygen from accepting electrons.

42. Which steps of cellular respiration produce $\text{CO}_2$?

    Pyruvate oxidation and the citric acid cycle. Decarboxylation reactions remove carbon atoms as $\text{CO}_2$.

43. What structural feature of mitochondria supports cellular respiration?

    Cristae increase surface area for the ETC. Folded inner membrane provides more space for ETC protein complexes.

44. Where does the Krebs cycle occur?

    Mitochondrial matrix. The innermost compartment of mitochondria where the cycle enzymes are located.

45. What are the three main stages of aerobic cellular respiration?

    Glycolysis, citric acid cycle, oxidative phosphorylation. These sequential stages completely oxidize glucose to maximize ATP yield.

46. How is the ETC linked to the Krebs cycle?

    NADH and FADH₂ transfer electrons to the ETC. Reduced coenzymes from Krebs cycle donate electrons to start ETC.

47. Where does the citric acid cycle occur in eukaryotic cells?

    Mitochondrial matrix. The inner compartment of mitochondria contains citric acid cycle enzymes.

48. How many ATP molecules are generated by the electron transport chain?

    Approximately 34 ATP molecules. Electron flow creates proton gradient that drives ATP synthase production.

49. What are the products of alcoholic fermentation from one pyruvate?

    Ethanol, $\text{CO}_2$, and NAD$^+$. Pyruvate is decarboxylated then reduced while regenerating NAD$^+$.

50. What is fermentation's main role when oxygen is unavailable?

    Regenerate NAD$^+$ so glycolysis can continue. NADH is oxidized back to NAD$^+$ without oxygen present.

51. Name one electron carrier used in cellular respiration.

    NAD⁺ or FAD. These molecules accept and transport electrons during metabolic oxidation.

52. What is chemiosmosis in mitochondria?

    ATP synthesis powered by $\text{H}^+$ diffusion through ATP synthase. Proton gradient drives ATP synthesis as protons flow through ATP synthase.

53. What is the role of NADH and FADH₂ in cellular respiration?

    Electron carriers. These molecules transport electrons from metabolic reactions to the ETC.

54. What is the main output of the Krebs cycle that proceeds to the ETC?

    NADH and FADH₂. These electron carriers feed into the ETC to generate most ATP.

55. How many turns of the citric acid cycle occur per glucose molecule?

    2 turns. Two acetyl-CoA molecules require two complete turns of the cycle.

56. What is the primary function of the citric acid cycle?

    Oxidize acetyl-CoA to $\text{CO}_2$ and reduce NAD$^+$ and FAD. The cycle harvests electrons while completely oxidizing the 2-carbon unit.

57. What is oxidative phosphorylation?

    ATP production driven by chemiosmosis and the ETC. Uses proton gradient energy to drive ATP synthesis via ATP synthase.

58. Identify the first stage of cellular respiration.

    Glycolysis. The initial breakdown of glucose occurs in the cytoplasm without oxygen.

59. How does chemiosmosis generate ATP?

    Proton gradient drives ATP synthesis. Protons flow back through ATP synthase, powering ATP formation.

60. Which electron carriers deliver high-energy electrons to the electron transport chain?

    NADH and FADH$_2$. These reduced carriers donate high-energy electrons to generate ATP.

61. Identify the final stage of cellular respiration.

    Electron transport chain (ETC). Electrons from NADH and FADH₂ flow through protein complexes to generate ATP.

62. Which coenzyme is reduced during glycolysis?

    NAD⁺ is reduced to NADH. NAD⁺ gains electrons and hydrogen to become NADH during glucose oxidation.

63. How many ATP molecules are produced in glycolysis?

    Net gain of 2 ATP molecules. 4 ATP are made but 2 are consumed, yielding a net gain of 2 ATP.

64. What is the net ATP yield from the citric acid cycle per glucose by substrate-level phosphorylation?

    2 ATP (or 2 GTP). Direct phosphorylation produces ATP without electron transport.

65. Which molecule is formed when oxygen accepts electrons?

    Water ($H_2O$). Oxygen combines with electrons and protons to form water as a byproduct.

66. Which molecule is a substrate for the Krebs cycle?

    Acetyl-CoA. The 2-carbon acetyl unit enters the cycle attached to Coenzyme A.

67. What is the net ATP yield per glucose in fermentation (glycolysis only)?

    Net 2 ATP per glucose. Only glycolysis operates without oxygen, producing limited ATP.

68. Identify one product of glycolysis besides ATP.

    NADH or Pyruvate. Glycolysis produces two pyruvate molecules and reduces NAD⁺ to NADH.

69. What is the primary energy currency in cells?

    ATP. Universal energy molecule that powers most cellular processes.

70. Identify the immediate products of glycolysis from one glucose molecule.

    2 pyruvate, 2 NADH, net 2 ATP. Glucose splits into two 3-carbon pyruvates while reducing NAD$^+$ and making ATP.

71. How many pyruvate molecules are produced per glucose in glycolysis?

    2 pyruvate. One glucose molecule splits into two 3-carbon pyruvate molecules.

72. What is the overall equation for cellular respiration?

    $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$. Glucose is oxidized with oxygen to produce carbon dioxide, water, and energy as ATP.

73. Identify the products of pyruvate oxidation per pyruvate molecule.

    1 acetyl-CoA, 1 NADH, 1 $\text{CO}_2$. Each pyruvate loses one carbon as $\text{CO}_2$ and reduces one NAD$^+$.

74. How many acetyl-CoA molecules enter the citric acid cycle per glucose?

    2 acetyl-CoA. Two pyruvate molecules are converted to two acetyl-CoA molecules.

75. What is the immediate substrate used by ATP synthase to make ATP?

    ADP and inorganic phosphate ($\text{P}_i$). ATP synthase phosphorylates ADP using energy from proton flow.

76. What occurs during oxidative phosphorylation?

    ATP is produced from ADP and inorganic phosphate. Electron transport creates proton gradient that drives ATP synthase.

77. What is the approximate ATP yield per NADH in many AP Biology contexts?

    About $2.5$ ATP per NADH. NADH passes through three proton-pumping complexes in the ETC.

78. Which mitochondrial compartment accumulates the highest $\text{H}^+$ concentration during ETC activity?

    Intermembrane space. Protons are pumped here from the matrix by ETC complexes.

79. Which stage of cellular respiration is anaerobic?

    Glycolysis. Only glycolysis can proceed without oxygen, unlike the other stages.

80. Where is the electron transport chain located in eukaryotic cells?

    Inner mitochondrial membrane. Protein complexes in this membrane pump protons and transfer electrons.

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