CH. 6 HOW CELLS RELEASE ENERGY

CHAPTER 6: HOW CELLS RELEASE ENERGY

Q: What are the three kinds of cellular respiration?
A: Aerobic respiration, anaerobic respiration, and fermentation.

Q: What are the three stages of aerobic cellular respiration?
A: Glycolysis, Krebs cycle (Citric Acid Cycle), and Electron Transport Chain (ETC)/Oxidative Phosphorylation.

Q: What is the balanced equation for aerobic cellular respiration?
A: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP

Q: What is glycolysis? Where does it occur? What is the net yield of ATP and NADH?
A: Glycolysis is the first step of respiration, occurring in the cytoplasm, where glucose is broken into 2 pyruvate molecules. Net yield: 2 ATP, 2 NADH.

Q: What are the two methods of ATP production?
A:

• Substrate-level phosphorylation (Direct ATP formation in glycolysis and Krebs cycle)

• Oxidative phosphorylation (ATP synthesis in Electron Transport Chain using a proton gradient)

Q: What happens during the second stage of aerobic respiration? What are the ATP, NADH, and FADH₂ yields?
A: The Krebs cycle (Citric Acid Cycle) occurs in the mitochondrial matrix, generating:

• 2 ATP

• 6 NADH

• 2 FADH₂

Q: What is the net ATP yield from aerobic cellular respiration?
A:

Q: Why do some cells produce only 36 ATP instead of 38?
A: NADH from glycolysis cannot cross the mitochondrial membrane directly. Instead, electrons are transferred to NAD⁺ or FAD inside the mitochondria. If transferred to FAD, only 36 ATP is produced (Liver, Heart, Kidney = 36 ATP; Brain, Skeletal Muscle = 38 ATP).

Q: What is the role of O₂ in respiration?
A: O₂ is the final electron acceptor in the Electron Transport Chain, allowing ATP production and forming H₂O.

Q: How do other food molecules enter respiration pathways?
A:

• Carbohydrates → Converted into glucose

• Proteins → Broken into amino acids, enter at various points

• Lipids → Broken into glycerol (enters glycolysis) and fatty acids (enter Krebs cycle)

Q: How is anaerobic respiration different from aerobic respiration?
A: Anaerobic respiration occurs without oxygen, using alternative electron acceptors, producing less ATP than aerobic respiration.

Q: What is fermentation? What are its two types? How many ATP are produced?
A: Fermentation is an anaerobic process that regenerates NAD⁺ for glycolysis. 2 ATP are produced.
Types:

• Lactic acid fermentation (occurs in muscles, produces lactate)

• Alcoholic fermentation (occurs in yeast, produces ethanol & CO₂)