Chapter 12: Respiration in Plants

Answer: The electron transport system (ETS) in plants helps in ATP synthesis by transferring energy-rich electrons through a series of protein complexes located in the mitochondrial membrane. The movement of electrons down the chain releases energy, which is used to pump protons across the membrane, creating a proton gradient. This gradient drives ATP synthesis as protons flow back through ATP synthase, combining ADP and inorganic phosphate to form ATP.

Answer: Aerobic respiration occurs in the presence of oxygen and involves the complete oxidation of glucose to carbon dioxide and water, yielding a significant amount of ATP. Fermentation, on the other hand, occurs in the absence of oxygen and results in the incomplete breakdown of glucose into ethanol or lactic acid, producing much less ATP. Aerobic respiration mainly takes place in the mitochondria, whereas fermentation occurs in the cytoplasm.

Answer: The Krebs cycle, also known as the citric acid cycle, is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. The cycle produces ATP, NADH, and FADH2, which are essential for the electron transport chain, and thus plays a critical role in energy production.

Answer: The respiratory quotient (RQ) is the ratio of carbon dioxide produced to oxygen consumed during respiration. Its value can indicate the type of substrate being metabolized: an RQ of 1 suggests carbohydrates are the primary substrates, while values less than 1 suggest a predominance of fats or proteins. Understanding RQ helps in assessing metabolic processes and adjustments in plants.

Answer: ATP is known as the energy currency of the cell because it stores and transports chemical energy within cells. It provides energy for various cellular processes by releasing its terminal phosphate group, which is then used to perform work such as muscle contraction, active transport, and biosynthesis.

Answer: ATP synthase is a complex enzyme located in the mitochondrial membrane that synthesizes ATP from ADP and inorganic phosphate. It uses the energy from the proton gradient created by the electron transport chain to catalyze this reaction. The flow of protons back into the mitochondrial matrix through ATP synthase provides the energy required for ATP production.

Answer: In the absence of oxygen, plant cells switch from aerobic respiration to anaerobic processes such as fermentation. During fermentation, glycolysis continues to produce pyruvate, which is then converted into ethanol or lactic acid. This process allows the regeneration of NAD+, ensuring glycolysis can continue to produce ATP anaerobically.

Answer: Glycolysis is the process of breaking down glucose into pyruvate, yielding ATP and NADH, and it occurs in the cytoplasm. The citric acid cycle, also known as the Krebs cycle, takes place in the mitochondrial matrix and further oxidizes pyruvate derivatives. It produces ATP, NADH, FADH2, and releases carbon dioxide.

Answer: Respiration is considered an amphibolic pathway because it involves both catabolic and anabolic processes. Catabolic reactions break down nutrients to produce energy, while anabolic reactions synthesize necessary cellular components using energy produced from catabolism. Therefore, respiration plays dual roles in energy extraction and biosynthesis.

Answer: Plants adapt their respiration processes by adjusting their metabolic activities based on environmental conditions. For example, they may switch between aerobic and anaerobic respiration depending on oxygen availability or alter the activity of enzymes involved in respiration to optimize energy production while minimizing stress or damage.