Photosynthesis and Cellular Respiration Questions PDF

1. A group of students are studying muscle cells during intense exercise. They began to notice that the muscle cells produce lactic acid. What does the production of lactic acid indicate what type of respiration is occurring in the muscle cells? (A) The muscle cells are undergoing fermentation du...

1. A group of students are studying muscle cells during intense exercise. They began to notice that the muscle cells produce lactic acid. What does the production of lactic acid indicate what type of respiration is occurring in the muscle cells? (A) The muscle cells are undergoing fermentation due to an inability to use the electron transport chain, producing lactic acid.(B) The muscle cells are undergoing fermentation due to an inability to use glycolysis, producing lactic acid.(C) The muscle cells are undergoing aerobic respiration due to an inability to use the electron transport chain, producing lactic acid.(D) The muscle cells are undergoing aerobic respiration due to an inability to perform the Krebs cycle, producing lactic acid.Answer: A 2. A group of researchers genetically modify a plant to enhance its ability to capture light energy and convert it into chemical energy. The modification increased the plant’s pigment production. What would be an immediate benefit of this modification? (A) The plant will absorb a larger range of light wavelengths, increasing the overall rate of photosynthesis.(B) The plant will produce more oxygen during photosynthesis, which could be toxic.(C) The plant will be able to perform pyruvic acid fermentation when light is unavailable.(D) The plant would generate more ATP because of a more efficient ATP synthase.Answer: A 3. Chlorophyll does which of the following processes during photosynthesis? (A) Generating electrons to pass down to photosystem I.(B) Breaking down glucose into hydrogen atoms and oxygen.(C) Absorbing sunlight energy to give to electrons for the electron transport chain.(D) Absorbing sunlight energy to give it to oxygen to generate a concentration gradient.Answer: C 4. A company wants to develop a plant that can grow more efficiently in low-water environments. Which modification could enhance the plant’s ability to perform photosynthesis with limited water? (A) The plant could use a more efficient C4 or CAM pathway, which reduces water loss by minimizing stomatal opening.(B) The plant's stomata would be modified to remain open for longer periods, allowing for more CO2 intake.(C) The plant would have larger leaves, increasing surface area for light absorption.(D) The plant would be engineered to produce more oxygen, enhancing photosynthesis.Answer: A 5. In enzyme-catalyzed reactions, which of the following factors can NOT increase the reaction rate? (A) Increasing the temperature within the optimal range.(B) Increasing the enzyme concentration up to a point.(C) Decreasing the activation energy of the reaction.(D) Increasing the substrate concentration up to a point of saturation.Answer: C 6. An enzyme is added to a solution where its substrate and product are in equilibrium. What will occur? (A) Nothing; the reaction will remain at equilibrium.(B) The free energy of the system will change.(C) The reaction will change from endergonic to exergonic.(D) Additional substrate will be formed.Answer: A 7. A scientist is designing an industrial process to convert cellulose into glucose using cellulase enzymes. The reaction is performed at a low pH, but the enzyme activity significantly decreases. Which of the following is the most likely reason for the decreased activity? (A) The enzyme has become denatured due to the low pH, altering its active site structure.(B) The substrate concentration was too low to allow proper enzyme binding.(C) The temperature was too high, causing the enzyme to become less efficient.(D) The enzyme is not receiving enough energy from ATP to catalyze the reaction.Answer: A 8. Almost all of CO2 from catabolism is released during (A) The citric acid cycle(B) Glycolysis(C) Lactate fermentation(D) Electron transport chainAnswer: A 9. Because the light reaction of photosynthesis generates high-energy electrons, which end up in ____ through linear electron flow. The light reactions also produce ____ and ____ (A) Water; Sugar, Oxygen(B) NADPH; ATP; Oxygen(C) ATP; NADPH; Oxygen(D) Chlorophyll; ATP; NADPHAnswer: B 10. Cells exposed to low oxygen conditions experience a shift in ATP production from oxidative phosphorylation to fermentation. However, some cells exhibit partial electron transport chain (ETC) function even under low oxygen conditions. Which of the following is the most likely reason for maintaining partial ETC function in low oxygen conditions? (A) To increase proton leakage, maintaining mitochondrial membrane potential without generating ATP.(B) To drive additional CO2 fixation, increasing the availability of intermediates for the citric acid cycle.(C) To allow for the continued regeneration of NAD+, reducing reliance on lactic acid fermentation.(D) Mr. Paine likes to fish.Answer: C 11. Dinitrophenol (DNP) is a chemical that allows protons to freely pass through the inner mitochondrial membrane, bypassing ATP synthase. What immediate effect does DNP have on cellular respiration? (A) NADH accumulates, since electron flow in the ETC halts due to the loss of the proton gradient.(B) Glycolysis slows down, as ATP feedback inhibition reduces phosphofructokinase activity.(C) ATP synthesis increases, as protons are more efficiently transferred across the mitochondrial membrane.(D) Oxygen consumption remains unchanged, but ATP production decreases due to a loss of proton gradient.Answer: D 12. Rubisco, an enzyme responsible for CO₂ fixation in the Calvin cycle, has an oxygenase activity that leads to photorespiration when oxygen levels are high. What is the primary consequence of this oxygenase function? (A) ATP and NADPH are wasted, and no glucose is produced, reducing overall photosynthetic efficiency.(B) The plant compensates by increasing cyclic electron flow, leading to excess ATP production.(C) Oxygen acts as a competitive inhibitor of RuBP carboxylation, enhancing CO₂ fixation rates.(D) Rubisco’s affinity for O₂ increases at low temperatures, making photorespiration more favorable.Answer: A 1. Both mitochondria and chloroplasts rely on chemiosmosis for ATP production, the direction of proton movement across membranes differs. How does the location of proton accumulation differ between these organelles? Mitochondria: Protons accumulate in the matrix; Chloroplasts: Protons accumulate in the cytoplasm. Mitochondria: Protons accumulate in the intermembrane space; Chloroplasts: Protons accumulate in the thylakoid lumen. Mitochondria: Protons accumulate in the inner membrane; Chloroplasts: Protons accumulate in the outer membrane. Mitochondria: Protons accumulate in the stroma; Chloroplasts: Protons accumulate in the thylakoid lumen. Answer: Mitochondria: Protons accumulate in the intermembrane space; Chloroplasts: Protons accumulate in the thylakoid lumen. 2. A mutant plant species, researchers observe that although the light-dependent reactions of photosynthesis proceed normally, the light-independent reactions fail to function. Which of the following could best explain this phenomenon? A defect in RuBisCO prevents the fixation of carbon dioxide into organic molecules. A mutation in plastocyanin prevents electron transfer from Photosystem II to Photosystem I. A lack of water limits the splitting of H₂O, preventing oxygen release. An overactive ATP synthase leads to excessive ATP production, disrupting metabolic balance. Answer: A defect in RuBisCO prevents the fixation of carbon dioxide into organic molecules. 3. During oxidative phosphorylation, NADH and FADH₂ donate electrons to the electron transport chain (ETC). However, FADH₂ contributes less ATP per molecule than NADH. What explains the difference in ATP yield between NADH and FADH₂? FADH₂ donates more electrons per molecule than NADH, but they bypass ATP synthase. FADH₂ generates ATP exclusively through substrate-level phosphorylation rather than oxidative phosphorylation. NADH undergoes a different redox reaction that yields more ATP per electron transferred. FADH₂ donates electrons later in the ETC than NADH, leading to fewer protons being pumped across the inner mitochondrial membrane. Answer: FADH₂ donates electrons later in the ETC than NADH, leading to fewer protons being pumped across the inner mitochondrial membrane. 4. C4 plants have evolved a specialized pathway to reduce photorespiration and improve photosynthetic efficiency in hot, arid environments. How does the C4 pathway reduce photorespiration compared to C3 plants? C4 plants directly use oxygen as an alternative electron acceptor in photosystem I, preventing photoinhibition. C4 plants have a higher affinity for oxygen in their RuBisCO enzyme, which prevents unnecessary ATP consumption. C4 plants spatially separate carbon fixation from the Calvin cycle, using PEP carboxylase to concentrate CO₂ in bundle sheath cells. C4 plants use a specialized enzyme to fix carbon at night and store it as malate for use during the day. Answer: C4 plants spatially separate carbon fixation from the Calvin cycle, using PEP carboxylase to concentrate CO₂ in bundle sheath cells. 5. How do C4 plants minimize the cost of photorespiration? Increasing the CO2 concentration around RuBisCo, and incorporating it into a four-carbon compound in the mesophyll cell. Convert energy from the sun into chemical energy, which is then stored in sugars. By using a special enzyme that increases the oxygen concentration of the chloroplasts. By separating the initial carbon fixation and Calvin cycle into different cells, reducing the oxygen exposure to the enzyme RuBisCO. Answer: Increasing the CO2 concentration around RuBisCo, and incorporating it into a four-carbon compound in the mesophyll cell. 6. What occurs when a pigment’s electrons become isolated? The electrons continue to transfer energy, allowing the pigment to photosynthesize independently. The pigment loses all its energy and becomes incapable of absorbing light. The electrons fall back into their ground state, giving off heat or light. The isolated electrons are immediately used to fix carbon dioxide into glucose. Answer: The electrons fall back into their ground state, giving off heat or light. 7. What is the difference between linear electron flow and cyclic electron flow? Linear electron flow uses one photosystem, producing O2; Cyclic electron flow uses one photosystem and produces ATP and NADPH. Linear and Cyclic electron flow use two photosystems, producing ATP and O2. Linear electron flow uses one photosystem, producing ATP; Cyclic electron flow uses two photosystems and produces O2. Linear electron flow uses two photosystems, producing ATP, NADPH, and O2; Cyclic electron flow uses one photosystem, producing ATP. Answer: Linear electron flow uses two photosystems, producing ATP, NADPH, and O2; Cyclic electron flow uses one photosystem, producing ATP. 8. In what way is photosynthesis a redox process? It allows electrons from light to be directly transferred into glucose. It involves the transfer of electrons where H2O is oxidized to produce O2, while CO2 is reduced to form sugar molecules. Oxygen molecules are oxidized to produce electrons, and glucose molecules are reduced to form ATP without the need for light. Involves the transfer of electrons from NADPH to H2O, causing the water to oxidize and release carbon dioxide into the atmosphere. Answer: It involves the transfer of electrons where H2O is oxidized to produce O2, while CO2 is reduced to form sugar molecules. 9. What occurs when the pH of the matrix increases? The electrons transport chain no longer functions, halting all cellular respiration processes. There is reduced O2 to water, causing the mitochondria to undergo fermentation instead of oxidative phosphorylation. The mitochondria no longer produces ATP. Electrons flow along the electron transport chains of the mitochondria. Answer: Electrons flow along the electron transport chains of the mitochondria. 10. How does the inner mitochondrial membrane generate and maintain the H+ gradient that drives ATP synthesis? By using light energy to pump protons from the matrix, creating a proton flow that directly powers ATP production through light-dependent reactions. Protons freely flow through the membrane which leads to a high concentration of H+ in the intermembrane space, directly driving ATP synthesis. Utilizing the EC chain, electrons pass a series of protein complexes embedded in the membrane, actively pumping protons from the matrix to the intermembrane space. Using ATP produced in the matrix to pump protons into intermembrane space, which then directly powers ATP synthases without and help from the EC chain. Answer: Utilizing the EC chain, electrons pass a series of protein complexes embedded in the membrane, actively pumping protons from the matrix to the intermembrane space. 11. What occurs when an allosteric active site becomes inactive? The enzyme can no longer be stabilized and is denatured. The enzyme’s overall activity increases because the allosteric site stop interacting with other molecules. The enzyme begins to catalyze reactions at a much higher rate due to a lower demand for cofactors. The original substrates can not react, but allosteric inhibitors stabilize the enzyme. Answer: The original substrates can not react, but allosteric inhibitors stabilize the enzyme. 12. What prevents molecules from spontaneously breaking down into less ordered, more stable molecules? High activation energy. Activation energy barriers. Constant production of energy through photosynthesis. Lack of chemical bonds. Answer: Activation energy barriers. 13. A cell is placed in a medium lacking oxygen but supplemented with a high concentration of glucose. What would be the expected impact on ATP production and the proton gradient? ATP production would rely on glycolysis only, leading to a buildup of NADH and no proton gradient formation. Oxidative phosphorylation would continue using an alternative electron acceptor, maintaining the proton. ATP production would increase due to substrate-level phosphorylation in the citric acid cycle. The cell would switch to photosynthesis to generate ATP and restore the proton gradient. Answer: ATP production would rely on glycolysis only, leading to a buildup of NADH and no proton gradient formation. 14. In the absence of oxygen, cells perform fermentation to regenerate NAD⁺ and allow glycolysis to continue. Which process directly generates ATP during fermentation? Substrate-level phosphorylation in glycolysis, converting ADP to ATP. Oxidative phosphorylation driven by a proton gradient across the mitochondrial membrane. Reduction of pyruvate to lactate, releasing free energy captured as ATP. Conversion of glucose to ethanol, which produces ATP as a byproduct. Answer: Substrate-level phosphorylation in glycolysis, converting ADP to ATP. 15. Despite its inefficiency, rubisco has not been naturally replaced by a more efficient carbon-fixing enzyme in most plants. Which of the following provides the most evolutionarily plausible explanation for rubisco’s persistence despite its oxygenase activity? The active site of rubisco is structurally incapable of modifications that would eliminate its oxygenase activity. Mutations in the rubisco gene tend to be lethal, preventing natural selection from favoring alternative carbon-fixing enzymes. Rubisco’s inefficiency is advantageous because photorespiration generates alternative metabolic intermediates needed in stressful conditions. Rubisco evolved when atmospheric oxygen levels were low, and selective pressure has not been strong enough to favor a complete replacement. Answer: Rubisco evolved when atmospheric oxygen levels were low, and selective pressure has not been strong enough to favor a complete replacement. 16. What is the primary role of water (H₂O) in the light-dependent reactions of photosynthesis? It donates electrons to replace those lost by chlorophyll in Photosystem II. It directly powers ATP synthase by donating protons to the thylakoid space. It acts as a carbon source for the Calvin cycle. It provides oxygen to be used as an electron acceptor in the electron transport chain. Answer: It donates electrons to replace those lost by chlorophyll in Photosystem II. 17. Which of the following acts as the oxidizing agent in the reaction listed below? Pyruvate + NADH + H+ →Lactate + NAD+ Lactate NAD+ NADH Pyruvate Answer: Pyruvate 18. Biochemists discover a compound that inhibits the action of ATP synthase. If this compound is added to a cell, which of the following will most likely occur? The citric acid cycle will increase in speed to produce more NADH and FADH2. The proton gradient across the inner mitochondrial membrane will dissipate, reducing the efficiency of oxidative phosphorylation. The cell will perform apoptosis immediately, utilizing lysosomes to break down the mitochondria. Oxygen consumption will increase because the cell tries to compensate for the loss of ATP. Answer: The proton gradient across the inner mitochondrial membrane will dissipate, reducing the efficiency of oxidative phosphorylation.