Respiration and Energy Transfer
Short Questions
1. What is respiration?
Answer: Respiration is a catabolic process that oxidizes organic substrates to produce energy as ATP.
2. Where does glycolysis occur in a cell?
Answer: Glycolysis occurs in the cytoplasm.
3. What is the net ATP yield from glycolysis?
Answer: Glycolysis yields a net of 2 ATP per glucose molecule.
4. What is anaerobic respiration also called?
Answer: Anaerobic respiration is also called fermentation.
5. What are the end products of alcoholic fermentation in yeast?
Answer: Ethanol and carbon dioxide are the end products.
6. Where does the Krebs cycle take place?
Answer: The Krebs cycle occurs in the mitochondrial matrix.
7. What is the role of oxygen in aerobic respiration?
Answer: Oxygen acts as the terminal electron acceptor in the electron transport chain.
8. What is the total ATP yield from aerobic respiration of one glucose?
Answer: Aerobic respiration yields up to 38 ATP per glucose molecule.
9. What is substrate-level phosphorylation?
Answer: It is the direct transfer of a phosphate group from a substrate to ADP to form ATP.
10. What is the respiratory quotient (RQ) for carbohydrates?
Answer: The RQ for carbohydrates is 1.
11. Which enzyme complex catalyzes pyruvate to Acetyl CoA conversion?
Answer: The pyruvate dehydrogenase complex catalyzes this conversion.
12. What is the primary process in respiration?
Answer: The primary process is the removal of hydrogen from respiratory substrates.
13. What is the RQ for fats?
Answer: The RQ for fats is approximately 0.7.
14. Which part of the mitochondria hosts the electron transport chain?
Answer: The inner mitochondrial membrane hosts the electron transport chain.
15. Why is the Krebs cycle called an amphibolic pathway?
Answer: It serves both catabolic (energy release) and anabolic (biosynthesis) functions.
Long Questions
1. Explain the process of glycolysis and its significance in respiration.
Answer: Glycolysis is the breakdown of one glucose molecule into two pyruvate molecules in the cytoplasm, producing 2 ATP and 2 NADH+H⁺. It is the first step in both aerobic and anaerobic respiration, providing pyruvate for further oxidation or fermentation. Its universal presence across organisms highlights its evolutionary significance.
2. How does anaerobic respiration differ from aerobic respiration in terms of energy yield?
Answer: Anaerobic respiration, or fermentation, yields only 2 ATP per glucose via glycolysis, as it lacks oxygen-dependent stages like the Krebs cycle and ETC. Aerobic respiration fully oxidizes glucose using oxygen, producing up to 38 ATP through glycolysis, Krebs cycle, and electron transport chain. This makes aerobic respiration far more efficient for energy production.
3. Describe the role of the electron transport chain in ATP production.
Answer: The electron transport chain (ETC) on the inner mitochondrial membrane oxidizes NADH+H⁺ and FADH₂, transferring electrons to oxygen, forming water. This process pumps protons, creating a gradient that drives ATP synthesis via chemiosmosis at the F0-F1 ATP synthase. The ETC produces approximately 34 ATP, the majority of the yield in aerobic respiration.
4. Why is the Krebs cycle considered a central metabolic pathway?
Answer: The Krebs cycle oxidizes Acetyl CoA to CO₂, producing energy carriers (6 NADH, 2 FADH₂, 2 GTP) per glucose in the mitochondrial matrix. Its intermediates, like α-ketoglutarate and oxaloacetate, are used for synthesizing amino acids and fatty acids, making it amphibolic. It also serves as a common pathway for carbohydrates, fats, and proteins via Acetyl CoA.
5. What is the significance of step-wise energy release in respiration?
Answer: Step-wise energy release allows efficient capture of energy as ATP, maximizing yield compared to rapid combustion. It enables regulation of energy output through enzyme control, meeting cellular needs. Additionally, intermediates from each step can be used for biosynthesis, supporting cellular functions.
6. How does fermentation in yeast differ from lactic acid fermentation in muscles?
Answer: In yeast, fermentation converts pyruvate to ethanol and CO₂, regenerating NAD⁺ for glycolysis, producing 2 ATP. In muscles, pyruvate is reduced to lactic acid during intense exercise, also regenerating NAD⁺ but causing fatigue. Yeast fermentation is used industrially, while lactic acid fermentation supports short bursts of energy in oxygen-scarce conditions.
7. Explain the role of coenzymes NAD⁺ and FAD in respiration.
Answer: NAD⁺ and FAD are electron carriers that accept electrons and protons during substrate oxidation in glycolysis, pyruvate oxidation, and Krebs cycle, forming NADH+H⁺ and FADH₂. These reduced coenzymes donate electrons to the electron transport chain, driving ATP synthesis. Their regeneration in the ETC ensures continuous respiration.
8. How does the respiratory quotient (RQ) vary with different substrates?
Answer: The RQ, the ratio of CO₂ released to O₂ consumed, is 1 for carbohydrates, as equal volumes are exchanged during oxidation. For fats, RQ is about 0.7, requiring more O₂ and producing less CO₂, while proteins have an RQ of about 0.9. In anaerobic respiration, RQ is infinite, as CO₂ is produced without O₂ consumption.
9. Discuss the importance of myoglobin in muscle respiration.
Answer: Myoglobin in red muscle fibers stores and transports oxygen, supporting sustained aerobic respiration for prolonged activities like marathon running. White muscle fibers, low in myoglobin, rely on glycolysis for rapid energy, suitable for sprinters but leading to lactic acid buildup. This distinction explains physiological adaptations in athletes.
10. How can you experimentally demonstrate anaerobic respiration in yeast?
Answer: Suspend yeast in a 10% glucose solution, cover with oil to exclude oxygen, and connect to lime water in a warm setup (37-38°C). The lime water turns milky due to CO₂ production, and an ethanol smell confirms fermentation after a day. This shows yeast respires anaerobically, producing ethanol and CO₂ without oxygen.
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