Photosynthesis & Cellular Respiration Questions PDF

During glycolysis, the enzyme phosphofructokinase (PFK) plays a key role in regulating the pathway by responding to ATP levels in the cell. Which of the following best describes how PFK functions? (A) PFK speeds up glycolysis when ATP levels are high by increasing glucose breakdown. (B) PFK slows...

During glycolysis, the enzyme phosphofructokinase (PFK) plays a key role in regulating the pathway by responding to ATP levels in the cell. Which of the following best describes how PFK functions? (A) PFK speeds up glycolysis when ATP levels are high by increasing glucose breakdown. (B) PFK slows down glycolysis when ATP levels are low to conserve energy for the cell. (C) PFK acts as an allosteric enzyme that is inhibited by ATP and activated by ADP, helping regulate energy production. (D) PFK is an enzyme that breaks down ATP into ADP to provide immediate energy for cellular processes. Answer: C Which of the following best describes the role of NADH and FADH₂ in cellular respiration? (A) They act as final electron acceptors in the electron transport chain, allowing ATP production to continue. (B) They donate high-energy electrons to the electron transport chain, driving the production of ATP. (C) They are enzymes that catalyze the breakdown of glucose into pyruvate during glycolysis. (D) They store excess ATP produced in the mitochondria for later use in anabolic reactions. Answer: B Which of the following best explains the role of the light-dependent reactions of photosynthesis? (A) They generate ATP and NADPH, which are then used to fix carbon in the Calvin cycle. (B) They directly produce glucose by splitting water molecules and capturing carbon dioxide. (C) They take place in the stroma of the chloroplast and fix carbon into organic molecules. (D) They involve glycolysis and fermentation to produce energy in the absence of oxygen. Answer: A A muscle cell is placed in an anaerobic environment and continues producing ATP, despite the absence of oxygen. Over time, the intracellular pH of the muscle cell decreases. What is the most likely explanation for this observation? (A) The accumulation of ATP in the cytoplasm leads to a drop in pH, causing the cell to switch to an alternative energy pathway. (B) Protons released from the electron transport chain in the absence of oxygen lower the intracellular pH, preventing further ATP production. (C) The buildup of lactic acid as a byproduct of fermentation lowers the pH, allowing glycolysis to continue producing ATP. (D) The citric acid cycle produces excess CO₂, which combines with water to form carbonic acid, decreasing intracellular pH. Answer: C A researcher studies mutant plant cells with a defective NADP⁺ reductase enzyme in the chloroplast. These mutant cells are exposed to light but show reduced rates of carbon fixation in the Calvin cycle. Which of the following best explains this observation? (A) The mutant cells cannot transport electrons from photosystem I to reduce NADP⁺, leading to a deficiency of NADPH needed for the Calvin cycle. (B) The mutant cells are unable to fix CO₂ because NADP⁺ directly captures carbon atoms during carbon fixation. (C) The light-dependent reactions no longer produce ATP, preventing the Calvin cycle from synthesizing glucose molecules. (D) The defective enzyme prevents the absorption of light energy in photosystem II, halting the production of NADPH and ATP. Answer: A Which term most precisely describes the cellular process of breaking down large molecules into smaller ones? (A) Metabolism (B) Anabolism (C) Catabolism (D) Hydrolysis Answer: C A group of researchers investigates the rate of oxygen evolution in algae under different wavelengths of light. They find that oxygen production is highest under red and blue light and lowest under green light. Which of the following best explains this observation? (A) Chlorophyll absorbs red and blue light efficiently but reflects green light, reducing photosynthesis. (B) The Calvin cycle operates more efficiently under red and blue light than under green light. (C) Photosystem I is only active under red and blue light, while photosystem II is inactive under green light. (D) Green light provides the optimal energy for breaking down water into oxygen and protons. Answer: A Which of the following experimental observations would provide the strongest evidence that ATP production in mitochondria depends on the presence of a proton gradient across the inner mitochondrial membrane? (A) ATP synthesis continues in isolated mitochondria that are provided with glucose and oxygen. (B) The addition of a compound that allows protons to move freely across the inner mitochondrial membrane decreases ATP production. (C) The amount of ATP produced is directly proportional to the amount of pyruvate added to a mitochondrial suspension. (D) Electron transport chain activity increases when NADH is supplied to mitochondria. Answer: B Which of the following best explains why oxygen is required for aerobic cellular respiration? (A) Oxygen is needed to break down glucose into ATP. (B) Oxygen is the final electron acceptor in the electron transport chain, allowing for continued ATP production. (C) Oxygen directly phosphorylates ADP into ATP during oxidative phosphorylation. (D) Oxygen provides energy to pump protons across the inner mitochondrial membrane. Answer: B Which of the following is an example of potential energy? (A) Heat released from a reaction (B) Movement of a muscle (C) Water rushing through a dam (D) A molecule of glucose Answer: D The first law of thermodynamics states that: (A) Energy can be created but not destroyed. (B) Energy cannot be created or destroyed, only transformed. (C) Every energy transfer increases entropy. (D) Energy transfers result in a net gain of heat. Answer: B A reaction with a negative ΔG is: (A) Endergonic and requires energy input. (B) Exergonic and releases energy. (C) At equilibrium and does not proceed. (D) Nonspontaneous and requires ATP. Answer: B Enzymes speed up chemical reactions by: (A) Increasing the temperature of the reaction. (B) Adding energy to the reaction. (C) Lowering the activation energy. (D) Increasing the ΔG of the reaction. Answer: C A competitive inhibitor works by: (A) Binding to the enzyme’s active site. (B) Binding to an allosteric site, changing enzyme shape. (C) Increasing substrate concentration. (D) Breaking down the enzyme. Answer: A An allosteric inhibitor decreases enzyme activity by: (A) Binding to a site other than the active site and changing enzyme shape. (B) Increasing the temperature of the reaction. (C) Outcompeting the substrate at the active site. (D) Breaking the enzyme into smaller pieces. Answer: A The primary purpose of cellular respiration is to: (A) Produce oxygen. (B) Break down ATP. (C) Convert chemical energy in glucose into ATP. (D) Generate carbon dioxide. Answer: C Which stage of cellular respiration produces the most ATP? (A) Glycolysis (B) Oxidative phosphorylation (Electron Transport Chain & Chemiosmosis) (C) Krebs Cycle (D) Fermentation Answer: B Where does glycolysis occur? (A) Cytoplasm (B) Mitochondrial matrix (C) Inner mitochondrial membrane (D) Nucleus Answer: A What is the net gain of ATP molecules from glycolysis? (A) 1 ATP (B) 2 ATP (C) 2 ATP (D) 4 ATP Answer: B During aerobic respiration, the final electron acceptor in the electron transport chain is: (A) NAD+ (B) Oxygen (O₂) (C) FADH₂ (D) ATP Answer: B The Krebs cycle occurs in the: (A) Cytoplasm (B) Inner mitochondrial membrane (C) Mitochondrial matrix (D) Stroma Answer: C Which process occurs in the absence of oxygen? (A) Oxidative phosphorylation (B) Fermentation (C) Krebs Cycle (D) Electron Transport Chain Answer: B What happens to pyruvate before it enters the Krebs cycle? (A) It gets reduced to lactic acid. (B) It is converted into Acetyl-CoA. (C) It undergoes phosphorylation. (D) It is used to produce oxygen. Answer: B How does the electron transport chain generate ATP? (A) By directly phosphorylating ADP. (B) By generating glucose. (C) By creating a proton gradient that powers ATP synthase. (D) By breaking down carbon dioxide. Answer: C Photosynthesis takes place in which organelle? (A) Mitochondria (B) Cytoplasm (C) Chloroplast (D) Ribosome Answer: C What is the primary function of the light-dependent reactions? (A) To produce ATP and NADPH for the Calvin cycle. (B) To fix carbon into glucose. (C) To produce oxygen for cellular respiration. (D) To break down water for energy. Answer: A Where does the Calvin cycle take place? (A) Thylakoid membrane (B) Stroma of the chloroplast (C) Mitochondrial matrix (D) Inner membrane of chloroplast Answer: B The enzyme that fixes carbon during the Calvin cycle is: (A) ATP synthase (B) RuBisCO (C) NADP+ reductase (D) Pyruvate dehydrogenase Answer: B Which molecule provides electrons to replace those lost by chlorophyll in Photosystem II? (A) Oxygen (B) Water (H₂O) (C) Glucose (D) NADPH Answer: B What is the main purpose of the Calvin cycle? (A) To produce ATP (B) To generate oxygen (C) To convert CO₂ into organic molecules like glucose (D) To release energy from glucose Answer: C