{ "chapter": "Biological Molecules", "count": 100, "answerIndex": "zero-based", "notice": "Original practice items including related concept variants; not official examination questions.", "questions": [ { "id": "water-solvent", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "Why can water transport many ions and polar molecules through blood plasma and cytoplasm?", "options": [ "Its polarity surrounds and separates charged particles", "Its molecules are non-polar", "It has no intermolecular attractions", "It converts every solute into a lipid" ], "answer": 0, "explanation": "Water is polar. Its partially charged regions form hydration shells around ions and interact with other polar substances, allowing them to remain dispersed in solution." }, { "id": "polysaccharide-hydrolysis", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "A storage polysaccharide is completely hydrolysed. Which change is expected in the reaction mixture?", "options": [ "Fewer reducing-sugar molecules", "More monosaccharide molecules", "More peptide bonds", "Formation of phospholipid bilayers" ], "answer": 1, "explanation": "Hydrolysis uses water to break glycosidic bonds, releasing the monosaccharide units from which the polysaccharide was built." }, { "id": "phospholipid-bilayer", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Phospholipids spontaneously form bilayers in water mainly because each molecule:", "options": [ "Is made entirely of amino acids", "Contains two hydrophilic tails", "Has a hydrophilic head and hydrophobic tails", "Forms covalent bonds with every neighbouring molecule" ], "answer": 2, "explanation": "The polar heads interact with water while the non-polar fatty-acid tails avoid it. This amphipathic character drives bilayer formation." }, { "id": "protein-denaturation-level", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "A globular protein is heat-denatured without hydrolysis. Which feature is most likely to remain intact?", "options": [ "Its precise active-site shape", "All hydrogen bonds", "Its normal tertiary structure", "The amino-acid sequence of each polypeptide" ], "answer": 3, "explanation": "Denaturation disrupts interactions that maintain secondary and tertiary structure, but it does not normally break the peptide bonds of the primary amino-acid sequence." }, { "id": "molecules-water-cohesion-outcome", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "Many hydrogen bonds form between neighbouring water molecules. Which outcome follows most directly?", "options": [ "Water shows strong cohesion and a relatively high surface tension", "Its temperature rises more slowly than that of many other small molecules", "A disaccharide and one molecule of water are formed", "A compact insoluble carbohydrate store accumulates" ], "answer": 0, "explanation": "Water shows strong cohesion and a relatively high surface tension. Each weak hydrogen bond contributes to a large cooperative attraction in bulk water." }, { "id": "molecules-water-cohesion-cause", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "Which change most directly explains this observation: water shows strong cohesion and a relatively high surface tension?", "options": [ "Heat energy is added to liquid water", "Many hydrogen bonds form between neighbouring water molecules", "Two monosaccharides join by a condensation reaction", "Plant cells convert many glucose molecules into starch" ], "answer": 1, "explanation": "Water shows strong cohesion and a relatively high surface tension. Each weak hydrogen bond contributes to a large cooperative attraction in bulk water." }, { "id": "molecules-water-cohesion-mechanism", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "After many hydrogen bonds form between neighbouring water molecules, which explanation best links the change to its outcome?", "options": [ "Much of the input energy first disrupts hydrogen-bond interactions", "A glycosidic bond forms as hydroxyl groups contribute hydrogen and hydroxyl", "Each weak hydrogen bond contributes to a large cooperative attraction in bulk water", "Polymerization reduces osmotic activity while coiling allows dense storage" ], "answer": 2, "explanation": "Water shows strong cohesion and a relatively high surface tension. Each weak hydrogen bond contributes to a large cooperative attraction in bulk water." }, { "id": "molecules-water-heat-capacity-outcome", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "After heat energy is added to liquid water, which observation is most likely?", "options": [ "A disaccharide and one molecule of water are formed", "A large energy yield becomes available", "A compact insoluble carbohydrate store accumulates", "Its temperature rises more slowly than that of many other small molecules" ], "answer": 3, "explanation": "Its temperature rises more slowly than that of many other small molecules. Much of the input energy first disrupts hydrogen-bond interactions." }, { "id": "molecules-water-heat-capacity-cause", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "A learner records that its temperature rises more slowly than that of many other small molecules. Which preceding event best accounts for it?", "options": [ "Heat energy is added to liquid water", "Plant cells convert many glucose molecules into starch", "Two monosaccharides join by a condensation reaction", "A cell oxidizes fatty acids from a triglyceride" ], "answer": 0, "explanation": "Its temperature rises more slowly than that of many other small molecules. Much of the input energy first disrupts hydrogen-bond interactions." }, { "id": "molecules-water-heat-capacity-mechanism", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "After heat energy is added to liquid water, which explanation best links the change to its outcome?", "options": [ "A glycosidic bond forms as hydroxyl groups contribute hydrogen and hydroxyl", "Much of the input energy first disrupts hydrogen-bond interactions", "Hydrocarbon chains contain many energy-rich carbon-hydrogen bonds", "Polymerization reduces osmotic activity while coiling allows dense storage" ], "answer": 1, "explanation": "Its temperature rises more slowly than that of many other small molecules. Much of the input energy first disrupts hydrogen-bond interactions." }, { "id": "molecules-water-heat-capacity-integrated", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "Which paired outcome and explanation best follows from this condition: heat energy is added to liquid water?", "options": [ "A compact insoluble carbohydrate store accumulates — Polymerization reduces osmotic activity while coiling allows dense storage", "A disaccharide and one molecule of water are formed — A glycosidic bond forms as hydroxyl groups contribute hydrogen and hydroxyl", "Its temperature rises more slowly than that of many other small molecules — Much of the input energy first disrupts hydrogen-bond interactions", "A large energy yield becomes available — Hydrocarbon chains contain many energy-rich carbon-hydrogen bonds" ], "answer": 2, "explanation": "Its temperature rises more slowly than that of many other small molecules. Much of the input energy first disrupts hydrogen-bond interactions." }, { "id": "molecules-condensation-outcome", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "A student models this change: Two monosaccharides join by a condensation reaction. What should the model predict first?", "options": [ "A compact insoluble carbohydrate store accumulates", "A large energy yield becomes available", "A peptide bond forms between the amino acids", "A disaccharide and one molecule of water are formed" ], "answer": 3, "explanation": "A disaccharide and one molecule of water are formed. A glycosidic bond forms as hydroxyl groups contribute hydrogen and hydroxyl." }, { "id": "molecules-condensation-cause", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "What is the most likely cause when a disaccharide and one molecule of water are formed?", "options": [ "Two monosaccharides join by a condensation reaction", "A cell oxidizes fatty acids from a triglyceride", "The amino group of one amino acid reacts with the carboxyl group of another", "Plant cells convert many glucose molecules into starch" ], "answer": 0, "explanation": "A disaccharide and one molecule of water are formed. A glycosidic bond forms as hydroxyl groups contribute hydrogen and hydroxyl." }, { "id": "molecules-condensation-mechanism", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "After two monosaccharides join by a condensation reaction, which explanation best links the change to its outcome?", "options": [ "Polymerization reduces osmotic activity while coiling allows dense storage", "A glycosidic bond forms as hydroxyl groups contribute hydrogen and hydroxyl", "Hydrocarbon chains contain many energy-rich carbon-hydrogen bonds", "A condensation reaction removes water and creates a covalent carbon-nitrogen link" ], "answer": 1, "explanation": "A disaccharide and one molecule of water are formed. A glycosidic bond forms as hydroxyl groups contribute hydrogen and hydroxyl." }, { "id": "molecules-condensation-integrated", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "Which paired outcome and explanation best follows from this condition: two monosaccharides join by a condensation reaction?", "options": [ "A compact insoluble carbohydrate store accumulates — Polymerization reduces osmotic activity while coiling allows dense storage", "A large energy yield becomes available — Hydrocarbon chains contain many energy-rich carbon-hydrogen bonds", "A disaccharide and one molecule of water are formed — A glycosidic bond forms as hydroxyl groups contribute hydrogen and hydroxyl", "A peptide bond forms between the amino acids — A condensation reaction removes water and creates a covalent carbon-nitrogen link" ], "answer": 2, "explanation": "A disaccharide and one molecule of water are formed. A glycosidic bond forms as hydroxyl groups contribute hydrogen and hydroxyl." }, { "id": "molecules-starch-storage-outcome", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "Which immediate result is most consistent with this condition: Plant cells convert many glucose molecules into starch?", "options": [ "A large energy yield becomes available", "A peptide bond forms between the amino acids", "Strong microfibrils develop in the plant cell wall", "A compact insoluble carbohydrate store accumulates" ], "answer": 3, "explanation": "A compact insoluble carbohydrate store accumulates. Polymerization reduces osmotic activity while coiling allows dense storage." }, { "id": "molecules-starch-storage-cause", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "Which condition would most specifically produce this result: a compact insoluble carbohydrate store accumulates?", "options": [ "Plant cells convert many glucose molecules into starch", "A cell oxidizes fatty acids from a triglyceride", "The amino group of one amino acid reacts with the carboxyl group of another", "Parallel cellulose chains form many hydrogen bonds with one another" ], "answer": 0, "explanation": "A compact insoluble carbohydrate store accumulates. Polymerization reduces osmotic activity while coiling allows dense storage." }, { "id": "molecules-starch-storage-mechanism", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "After plant cells convert many glucose molecules into starch, which explanation best links the change to its outcome?", "options": [ "Hydrocarbon chains contain many energy-rich carbon-hydrogen bonds", "Polymerization reduces osmotic activity while coiling allows dense storage", "A condensation reaction removes water and creates a covalent carbon-nitrogen link", "Cross-linking distributes tension across long unbranched beta-glucose polymers" ], "answer": 1, "explanation": "A compact insoluble carbohydrate store accumulates. Polymerization reduces osmotic activity while coiling allows dense storage." }, { "id": "molecules-starch-storage-integrated", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "Which paired outcome and explanation best follows from this condition: plant cells convert many glucose molecules into starch?", "options": [ "A large energy yield becomes available — Hydrocarbon chains contain many energy-rich carbon-hydrogen bonds", "A peptide bond forms between the amino acids — A condensation reaction removes water and creates a covalent carbon-nitrogen link", "A compact insoluble carbohydrate store accumulates — Polymerization reduces osmotic activity while coiling allows dense storage", "Strong microfibrils develop in the plant cell wall — Cross-linking distributes tension across long unbranched beta-glucose polymers" ], "answer": 2, "explanation": "A compact insoluble carbohydrate store accumulates. Polymerization reduces osmotic activity while coiling allows dense storage." }, { "id": "molecules-triglyceride-energy-outcome", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "A cell oxidizes fatty acids from a triglyceride. Which outcome follows most directly?", "options": [ "Glucose units can be added or removed rapidly at multiple ends", "A peptide bond forms between the amino acids", "Strong microfibrils develop in the plant cell wall", "A large energy yield becomes available" ], "answer": 3, "explanation": "A large energy yield becomes available. Hydrocarbon chains contain many energy-rich carbon-hydrogen bonds." }, { "id": "molecules-triglyceride-energy-cause", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "Which change most directly explains this observation: a large energy yield becomes available?", "options": [ "A cell oxidizes fatty acids from a triglyceride", "The amino group of one amino acid reacts with the carboxyl group of another", "Parallel cellulose chains form many hydrogen bonds with one another", "Glycogen contains many branch points" ], "answer": 0, "explanation": "A large energy yield becomes available. Hydrocarbon chains contain many energy-rich carbon-hydrogen bonds." }, { "id": "molecules-triglyceride-energy-mechanism", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "After a cell oxidizes fatty acids from a triglyceride, which explanation best links the change to its outcome?", "options": [ "A condensation reaction removes water and creates a covalent carbon-nitrogen link", "Hydrocarbon chains contain many energy-rich carbon-hydrogen bonds", "Cross-linking distributes tension across long unbranched beta-glucose polymers", "Branching creates numerous terminal sites accessible to metabolic enzymes" ], "answer": 1, "explanation": "A large energy yield becomes available. Hydrocarbon chains contain many energy-rich carbon-hydrogen bonds." }, { "id": "molecules-triglyceride-energy-integrated", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "Which paired outcome and explanation best follows from this condition: a cell oxidizes fatty acids from a triglyceride?", "options": [ "A peptide bond forms between the amino acids — A condensation reaction removes water and creates a covalent carbon-nitrogen link", "Strong microfibrils develop in the plant cell wall — Cross-linking distributes tension across long unbranched beta-glucose polymers", "A large energy yield becomes available — Hydrocarbon chains contain many energy-rich carbon-hydrogen bonds", "Glucose units can be added or removed rapidly at multiple ends — Branching creates numerous terminal sites accessible to metabolic enzymes" ], "answer": 2, "explanation": "A large energy yield becomes available. Hydrocarbon chains contain many energy-rich carbon-hydrogen bonds." }, { "id": "molecules-amino-acid-link-outcome", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "After the amino group of one amino acid reacts with the carboxyl group of another, which observation is most likely?", "options": [ "Strong microfibrils develop in the plant cell wall", "The phospholipids pack less tightly and membrane fluidity increases", "Glucose units can be added or removed rapidly at multiple ends", "A peptide bond forms between the amino acids" ], "answer": 3, "explanation": "A peptide bond forms between the amino acids. A condensation reaction removes water and creates a covalent carbon-nitrogen link." }, { "id": "molecules-amino-acid-link-cause", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "A learner records that a peptide bond forms between the amino acids. Which preceding event best accounts for it?", "options": [ "The amino group of one amino acid reacts with the carboxyl group of another", "Glycogen contains many branch points", "Parallel cellulose chains form many hydrogen bonds with one another", "Cis double bonds occur in membrane fatty-acid tails" ], "answer": 0, "explanation": "A peptide bond forms between the amino acids. A condensation reaction removes water and creates a covalent carbon-nitrogen link." }, { "id": "molecules-amino-acid-link-mechanism", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "After the amino group of one amino acid reacts with the carboxyl group of another, which explanation best links the change to its outcome?", "options": [ "Cross-linking distributes tension across long unbranched beta-glucose polymers", "A condensation reaction removes water and creates a covalent carbon-nitrogen link", "Double-bond kinks prevent close alignment of adjacent hydrocarbon chains", "Branching creates numerous terminal sites accessible to metabolic enzymes" ], "answer": 1, "explanation": "A peptide bond forms between the amino acids. A condensation reaction removes water and creates a covalent carbon-nitrogen link." }, { "id": "molecules-amino-acid-link-integrated", "chapter": "Biological Molecules", "difficulty": "Foundation", "stem": "Which paired outcome and explanation best follows from this condition: the amino group of one amino acid reacts with the carboxyl group of another?", "options": [ "Glucose units can be added or removed rapidly at multiple ends — Branching creates numerous terminal sites accessible to metabolic enzymes", "Strong microfibrils develop in the plant cell wall — Cross-linking distributes tension across long unbranched beta-glucose polymers", "A peptide bond forms between the amino acids — A condensation reaction removes water and creates a covalent carbon-nitrogen link", "The phospholipids pack less tightly and membrane fluidity increases — Double-bond kinks prevent close alignment of adjacent hydrocarbon chains" ], "answer": 2, "explanation": "A peptide bond forms between the amino acids. A condensation reaction removes water and creates a covalent carbon-nitrogen link." }, { "id": "molecules-cellulose-strength-outcome", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "A student models this change: Parallel cellulose chains form many hydrogen bonds with one another. What should the model predict first?", "options": [ "Glucose units can be added or removed rapidly at multiple ends", "The phospholipids pack less tightly and membrane fluidity increases", "Extreme changes in membrane fluidity are reduced", "Strong microfibrils develop in the plant cell wall" ], "answer": 3, "explanation": "Strong microfibrils develop in the plant cell wall. Cross-linking distributes tension across long unbranched beta-glucose polymers." }, { "id": "molecules-cellulose-strength-cause", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "What is the most likely cause when strong microfibrils develop in the plant cell wall?", "options": [ "Parallel cellulose chains form many hydrogen bonds with one another", "Cis double bonds occur in membrane fatty-acid tails", "Cholesterol is inserted among phospholipids in an animal membrane", "Glycogen contains many branch points" ], "answer": 0, "explanation": "Strong microfibrils develop in the plant cell wall. Cross-linking distributes tension across long unbranched beta-glucose polymers." }, { "id": "molecules-cellulose-strength-mechanism", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After parallel cellulose chains form many hydrogen bonds with one another, which explanation best links the change to its outcome?", "options": [ "Branching creates numerous terminal sites accessible to metabolic enzymes", "Cross-linking distributes tension across long unbranched beta-glucose polymers", "Double-bond kinks prevent close alignment of adjacent hydrocarbon chains", "Its rigid structure restrains movement at high temperature and prevents tight packing at low temperature" ], "answer": 1, "explanation": "Strong microfibrils develop in the plant cell wall. Cross-linking distributes tension across long unbranched beta-glucose polymers." }, { "id": "molecules-glycogen-branching-outcome", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which immediate result is most consistent with this condition: Glycogen contains many branch points?", "options": [ "The phospholipids pack less tightly and membrane fluidity increases", "Extreme changes in membrane fluidity are reduced", "Glucose units can be added or removed rapidly at multiple ends", "Protein folding or function may change" ], "answer": 2, "explanation": "Glucose units can be added or removed rapidly at multiple ends. Branching creates numerous terminal sites accessible to metabolic enzymes." }, { "id": "molecules-glycogen-branching-cause", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which condition would most specifically produce this result: glucose units can be added or removed rapidly at multiple ends?", "options": [ "A mutation replaces one amino acid in a polypeptide", "Cis double bonds occur in membrane fatty-acid tails", "Cholesterol is inserted among phospholipids in an animal membrane", "Glycogen contains many branch points" ], "answer": 3, "explanation": "Glucose units can be added or removed rapidly at multiple ends. Branching creates numerous terminal sites accessible to metabolic enzymes." }, { "id": "molecules-glycogen-branching-mechanism", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After glycogen contains many branch points, which explanation best links the change to its outcome?", "options": [ "Branching creates numerous terminal sites accessible to metabolic enzymes", "Double-bond kinks prevent close alignment of adjacent hydrocarbon chains", "Its rigid structure restrains movement at high temperature and prevents tight packing at low temperature", "Primary sequence determines side-chain interactions that establish higher levels of structure" ], "answer": 0, "explanation": "Glucose units can be added or removed rapidly at multiple ends. Branching creates numerous terminal sites accessible to metabolic enzymes." }, { "id": "molecules-glycogen-branching-integrated", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which paired outcome and explanation best follows from this condition: glycogen contains many branch points?", "options": [ "The phospholipids pack less tightly and membrane fluidity increases — Double-bond kinks prevent close alignment of adjacent hydrocarbon chains", "Glucose units can be added or removed rapidly at multiple ends — Branching creates numerous terminal sites accessible to metabolic enzymes", "Extreme changes in membrane fluidity are reduced — Its rigid structure restrains movement at high temperature and prevents tight packing at low temperature", "Protein folding or function may change — Primary sequence determines side-chain interactions that establish higher levels of structure" ], "answer": 1, "explanation": "Glucose units can be added or removed rapidly at multiple ends. Branching creates numerous terminal sites accessible to metabolic enzymes." }, { "id": "molecules-unsaturated-fat-outcome", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Cis double bonds occur in membrane fatty-acid tails. Which outcome follows most directly?", "options": [ "Protein folding or function may change", "Extreme changes in membrane fluidity are reduced", "The phospholipids pack less tightly and membrane fluidity increases", "A covalent disulfide bridge can stabilize the protein" ], "answer": 2, "explanation": "The phospholipids pack less tightly and membrane fluidity increases. Double-bond kinks prevent close alignment of adjacent hydrocarbon chains." }, { "id": "molecules-unsaturated-fat-cause", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which change most directly explains this observation: the phospholipids pack less tightly and membrane fluidity increases?", "options": [ "Cholesterol is inserted among phospholipids in an animal membrane", "Two cysteine side chains become oxidized near each other", "A mutation replaces one amino acid in a polypeptide", "Cis double bonds occur in membrane fatty-acid tails" ], "answer": 3, "explanation": "The phospholipids pack less tightly and membrane fluidity increases. Double-bond kinks prevent close alignment of adjacent hydrocarbon chains." }, { "id": "molecules-unsaturated-fat-mechanism", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After cis double bonds occur in membrane fatty-acid tails, which explanation best links the change to its outcome?", "options": [ "Double-bond kinks prevent close alignment of adjacent hydrocarbon chains", "Primary sequence determines side-chain interactions that establish higher levels of structure", "Its rigid structure restrains movement at high temperature and prevents tight packing at low temperature", "Sulfur atoms link distant parts of one chain or separate polypeptide chains" ], "answer": 0, "explanation": "The phospholipids pack less tightly and membrane fluidity increases. Double-bond kinks prevent close alignment of adjacent hydrocarbon chains." }, { "id": "molecules-unsaturated-fat-integrated", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which paired outcome and explanation best follows from this condition: cis double bonds occur in membrane fatty-acid tails?", "options": [ "Extreme changes in membrane fluidity are reduced — Its rigid structure restrains movement at high temperature and prevents tight packing at low temperature", "The phospholipids pack less tightly and membrane fluidity increases — Double-bond kinks prevent close alignment of adjacent hydrocarbon chains", "A covalent disulfide bridge can stabilize the protein — Sulfur atoms link distant parts of one chain or separate polypeptide chains", "Protein folding or function may change — Primary sequence determines side-chain interactions that establish higher levels of structure" ], "answer": 1, "explanation": "The phospholipids pack less tightly and membrane fluidity increases. Double-bond kinks prevent close alignment of adjacent hydrocarbon chains." }, { "id": "molecules-cholesterol-buffer-outcome", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After cholesterol is inserted among phospholipids in an animal membrane, which observation is most likely?", "options": [ "Protein folding or function may change", "A covalent disulfide bridge can stabilize the protein", "Extreme changes in membrane fluidity are reduced", "The protein can remain dispersed in an aqueous cytoplasm" ], "answer": 2, "explanation": "Extreme changes in membrane fluidity are reduced. Its rigid structure restrains movement at high temperature and prevents tight packing at low temperature." }, { "id": "molecules-cholesterol-buffer-cause", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "A learner records that extreme changes in membrane fluidity are reduced. Which preceding event best accounts for it?", "options": [ "A mutation replaces one amino acid in a polypeptide", "Two cysteine side chains become oxidized near each other", "A globular protein folds with hydrophilic groups exposed", "Cholesterol is inserted among phospholipids in an animal membrane" ], "answer": 3, "explanation": "Extreme changes in membrane fluidity are reduced. Its rigid structure restrains movement at high temperature and prevents tight packing at low temperature." }, { "id": "molecules-cholesterol-buffer-mechanism", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After cholesterol is inserted among phospholipids in an animal membrane, which explanation best links the change to its outcome?", "options": [ "Its rigid structure restrains movement at high temperature and prevents tight packing at low temperature", "Sulfur atoms link distant parts of one chain or separate polypeptide chains", "Polar and charged side chains form favourable interactions with surrounding water", "Primary sequence determines side-chain interactions that establish higher levels of structure" ], "answer": 0, "explanation": "Extreme changes in membrane fluidity are reduced. Its rigid structure restrains movement at high temperature and prevents tight packing at low temperature." }, { "id": "molecules-cholesterol-buffer-integrated", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which paired outcome and explanation best follows from this condition: cholesterol is inserted among phospholipids in an animal membrane?", "options": [ "Protein folding or function may change — Primary sequence determines side-chain interactions that establish higher levels of structure", "Extreme changes in membrane fluidity are reduced — Its rigid structure restrains movement at high temperature and prevents tight packing at low temperature", "A covalent disulfide bridge can stabilize the protein — Sulfur atoms link distant parts of one chain or separate polypeptide chains", "The protein can remain dispersed in an aqueous cytoplasm — Polar and charged side chains form favourable interactions with surrounding water" ], "answer": 1, "explanation": "Extreme changes in membrane fluidity are reduced. Its rigid structure restrains movement at high temperature and prevents tight packing at low temperature." }, { "id": "molecules-protein-primary-outcome", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "A student models this change: A mutation replaces one amino acid in a polypeptide. What should the model predict first?", "options": [ "A covalent disulfide bridge can stabilize the protein", "The protein can remain dispersed in an aqueous cytoplasm", "Protein folding or function may change", "The resulting fibres resist stretching" ], "answer": 2, "explanation": "Protein folding or function may change. Primary sequence determines side-chain interactions that establish higher levels of structure." }, { "id": "molecules-protein-primary-cause", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "What is the most likely cause when protein folding or function may change?", "options": [ "Two cysteine side chains become oxidized near each other", "A globular protein folds with hydrophilic groups exposed", "Three collagen polypeptides wind into a cross-linked triple helix", "A mutation replaces one amino acid in a polypeptide" ], "answer": 3, "explanation": "Protein folding or function may change. Primary sequence determines side-chain interactions that establish higher levels of structure." }, { "id": "molecules-protein-primary-mechanism", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After a mutation replaces one amino acid in a polypeptide, which explanation best links the change to its outcome?", "options": [ "Primary sequence determines side-chain interactions that establish higher levels of structure", "Sulfur atoms link distant parts of one chain or separate polypeptide chains", "Polar and charged side chains form favourable interactions with surrounding water", "The rope-like arrangement and covalent cross-links provide high tensile strength" ], "answer": 0, "explanation": "Protein folding or function may change. Primary sequence determines side-chain interactions that establish higher levels of structure." }, { "id": "molecules-protein-primary-integrated", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which paired outcome and explanation best follows from this condition: a mutation replaces one amino acid in a polypeptide?", "options": [ "A covalent disulfide bridge can stabilize the protein — Sulfur atoms link distant parts of one chain or separate polypeptide chains", "Protein folding or function may change — Primary sequence determines side-chain interactions that establish higher levels of structure", "The protein can remain dispersed in an aqueous cytoplasm — Polar and charged side chains form favourable interactions with surrounding water", "The resulting fibres resist stretching — The rope-like arrangement and covalent cross-links provide high tensile strength" ], "answer": 1, "explanation": "Protein folding or function may change. Primary sequence determines side-chain interactions that establish higher levels of structure." }, { "id": "molecules-disulfide-bond-outcome", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which immediate result is most consistent with this condition: Two cysteine side chains become oxidized near each other?", "options": [ "The protein can remain dispersed in an aqueous cytoplasm", "The resulting fibres resist stretching", "A covalent disulfide bridge can stabilize the protein", "Each strand can act as a template for a complementary strand" ], "answer": 2, "explanation": "A covalent disulfide bridge can stabilize the protein. Sulfur atoms link distant parts of one chain or separate polypeptide chains." }, { "id": "molecules-disulfide-bond-cause", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which condition would most specifically produce this result: a covalent disulfide bridge can stabilize the protein?", "options": [ "The two DNA strands separate without breaking their phosphodiester backbones", "A globular protein folds with hydrophilic groups exposed", "Three collagen polypeptides wind into a cross-linked triple helix", "Two cysteine side chains become oxidized near each other" ], "answer": 3, "explanation": "A covalent disulfide bridge can stabilize the protein. Sulfur atoms link distant parts of one chain or separate polypeptide chains." }, { "id": "molecules-disulfide-bond-mechanism", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After two cysteine side chains become oxidized near each other, which explanation best links the change to its outcome?", "options": [ "Sulfur atoms link distant parts of one chain or separate polypeptide chains", "Polar and charged side chains form favourable interactions with surrounding water", "The rope-like arrangement and covalent cross-links provide high tensile strength", "Specific adenine-thymine and cytosine-guanine pairing preserves sequence information" ], "answer": 0, "explanation": "A covalent disulfide bridge can stabilize the protein. Sulfur atoms link distant parts of one chain or separate polypeptide chains." }, { "id": "molecules-disulfide-bond-integrated", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which paired outcome and explanation best follows from this condition: two cysteine side chains become oxidized near each other?", "options": [ "The protein can remain dispersed in an aqueous cytoplasm — Polar and charged side chains form favourable interactions with surrounding water", "A covalent disulfide bridge can stabilize the protein — Sulfur atoms link distant parts of one chain or separate polypeptide chains", "The resulting fibres resist stretching — The rope-like arrangement and covalent cross-links provide high tensile strength", "Each strand can act as a template for a complementary strand — Specific adenine-thymine and cytosine-guanine pairing preserves sequence information" ], "answer": 1, "explanation": "A covalent disulfide bridge can stabilize the protein. Sulfur atoms link distant parts of one chain or separate polypeptide chains." }, { "id": "molecules-globular-solubility-outcome", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "A globular protein folds with hydrophilic groups exposed. Which outcome follows most directly?", "options": [ "Each strand can act as a template for a complementary strand", "The resulting fibres resist stretching", "The protein can remain dispersed in an aqueous cytoplasm", "Usable free energy can be coupled to cellular work" ], "answer": 2, "explanation": "The protein can remain dispersed in an aqueous cytoplasm. Polar and charged side chains form favourable interactions with surrounding water." }, { "id": "molecules-globular-solubility-cause", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which change most directly explains this observation: the protein can remain dispersed in an aqueous cytoplasm?", "options": [ "Three collagen polypeptides wind into a cross-linked triple helix", "ATP is hydrolysed to ADP and inorganic phosphate", "The two DNA strands separate without breaking their phosphodiester backbones", "A globular protein folds with hydrophilic groups exposed" ], "answer": 3, "explanation": "The protein can remain dispersed in an aqueous cytoplasm. Polar and charged side chains form favourable interactions with surrounding water." }, { "id": "molecules-globular-solubility-mechanism", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After a globular protein folds with hydrophilic groups exposed, which explanation best links the change to its outcome?", "options": [ "Polar and charged side chains form favourable interactions with surrounding water", "Specific adenine-thymine and cytosine-guanine pairing preserves sequence information", "The rope-like arrangement and covalent cross-links provide high tensile strength", "Products are more stable and phosphorylation can alter the reactivity of another molecule" ], "answer": 0, "explanation": "The protein can remain dispersed in an aqueous cytoplasm. Polar and charged side chains form favourable interactions with surrounding water." }, { "id": "molecules-collagen-structure-outcome", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After three collagen polypeptides wind into a cross-linked triple helix, which observation is most likely?", "options": [ "Each strand can act as a template for a complementary strand", "The resulting fibres resist stretching", "Usable free energy can be coupled to cellular work", "The blue reagent forms a green-to-brick-red precipitate depending on concentration" ], "answer": 1, "explanation": "The resulting fibres resist stretching. The rope-like arrangement and covalent cross-links provide high tensile strength." }, { "id": "molecules-collagen-structure-cause", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "A learner records that the resulting fibres resist stretching. Which preceding event best accounts for it?", "options": [ "The two DNA strands separate without breaking their phosphodiester backbones", "ATP is hydrolysed to ADP and inorganic phosphate", "Three collagen polypeptides wind into a cross-linked triple helix", "A heated sample containing a reducing sugar is mixed with Benedict's reagent" ], "answer": 2, "explanation": "The resulting fibres resist stretching. The rope-like arrangement and covalent cross-links provide high tensile strength." }, { "id": "molecules-collagen-structure-mechanism", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After three collagen polypeptides wind into a cross-linked triple helix, which explanation best links the change to its outcome?", "options": [ "Specific adenine-thymine and cytosine-guanine pairing preserves sequence information", "Products are more stable and phosphorylation can alter the reactivity of another molecule", "The sugar reduces copper(II) ions to insoluble copper(I) oxide", "The rope-like arrangement and covalent cross-links provide high tensile strength" ], "answer": 3, "explanation": "The resulting fibres resist stretching. The rope-like arrangement and covalent cross-links provide high tensile strength." }, { "id": "molecules-collagen-structure-integrated", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which paired outcome and explanation best follows from this condition: three collagen polypeptides wind into a cross-linked triple helix?", "options": [ "The resulting fibres resist stretching — The rope-like arrangement and covalent cross-links provide high tensile strength", "Each strand can act as a template for a complementary strand — Specific adenine-thymine and cytosine-guanine pairing preserves sequence information", "Usable free energy can be coupled to cellular work — Products are more stable and phosphorylation can alter the reactivity of another molecule", "The blue reagent forms a green-to-brick-red precipitate depending on concentration — The sugar reduces copper(II) ions to insoluble copper(I) oxide" ], "answer": 0, "explanation": "The resulting fibres resist stretching. The rope-like arrangement and covalent cross-links provide high tensile strength." }, { "id": "molecules-dna-base-pair-outcome", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "A student models this change: The two DNA strands separate without breaking their phosphodiester backbones. What should the model predict first?", "options": [ "Usable free energy can be coupled to cellular work", "Each strand can act as a template for a complementary strand", "The blue reagent forms a green-to-brick-red precipitate depending on concentration", "A lilac or purple colour develops" ], "answer": 1, "explanation": "Each strand can act as a template for a complementary strand. Specific adenine-thymine and cytosine-guanine pairing preserves sequence information." }, { "id": "molecules-dna-base-pair-cause", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "What is the most likely cause when each strand can act as a template for a complementary strand?", "options": [ "ATP is hydrolysed to ADP and inorganic phosphate", "A heated sample containing a reducing sugar is mixed with Benedict's reagent", "The two DNA strands separate without breaking their phosphodiester backbones", "A sample with many peptide bonds is treated with Biuret reagent" ], "answer": 2, "explanation": "Each strand can act as a template for a complementary strand. Specific adenine-thymine and cytosine-guanine pairing preserves sequence information." }, { "id": "molecules-dna-base-pair-mechanism", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After the two DNA strands separate without breaking their phosphodiester backbones, which explanation best links the change to its outcome?", "options": [ "Copper ions form coloured complexes with peptide-bond nitrogens in alkaline conditions", "Products are more stable and phosphorylation can alter the reactivity of another molecule", "The sugar reduces copper(II) ions to insoluble copper(I) oxide", "Specific adenine-thymine and cytosine-guanine pairing preserves sequence information" ], "answer": 3, "explanation": "Each strand can act as a template for a complementary strand. Specific adenine-thymine and cytosine-guanine pairing preserves sequence information." }, { "id": "molecules-dna-base-pair-integrated", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which paired outcome and explanation best follows from this condition: the two DNA strands separate without breaking their phosphodiester backbones?", "options": [ "Each strand can act as a template for a complementary strand — Specific adenine-thymine and cytosine-guanine pairing preserves sequence information", "Usable free energy can be coupled to cellular work — Products are more stable and phosphorylation can alter the reactivity of another molecule", "The blue reagent forms a green-to-brick-red precipitate depending on concentration — The sugar reduces copper(II) ions to insoluble copper(I) oxide", "A lilac or purple colour develops — Copper ions form coloured complexes with peptide-bond nitrogens in alkaline conditions" ], "answer": 0, "explanation": "Each strand can act as a template for a complementary strand. Specific adenine-thymine and cytosine-guanine pairing preserves sequence information." }, { "id": "molecules-atp-hydrolysis-outcome", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which immediate result is most consistent with this condition: ATP is hydrolysed to ADP and inorganic phosphate?", "options": [ "The blue reagent forms a green-to-brick-red precipitate depending on concentration", "Usable free energy can be coupled to cellular work", "They can spontaneously form sealed bilayers or vesicles", "A lilac or purple colour develops" ], "answer": 1, "explanation": "Usable free energy can be coupled to cellular work. Products are more stable and phosphorylation can alter the reactivity of another molecule." }, { "id": "molecules-atp-hydrolysis-cause", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which condition would most specifically produce this result: usable free energy can be coupled to cellular work?", "options": [ "A sample with many peptide bonds is treated with Biuret reagent", "A heated sample containing a reducing sugar is mixed with Benedict's reagent", "ATP is hydrolysed to ADP and inorganic phosphate", "Phospholipids are dispersed in water" ], "answer": 2, "explanation": "Usable free energy can be coupled to cellular work. Products are more stable and phosphorylation can alter the reactivity of another molecule." }, { "id": "molecules-atp-hydrolysis-mechanism", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After ATP is hydrolysed to ADP and inorganic phosphate, which explanation best links the change to its outcome?", "options": [ "The sugar reduces copper(II) ions to insoluble copper(I) oxide", "Hydrophilic heads face water while hydrophobic tails cluster away from it", "Copper ions form coloured complexes with peptide-bond nitrogens in alkaline conditions", "Products are more stable and phosphorylation can alter the reactivity of another molecule" ], "answer": 3, "explanation": "Usable free energy can be coupled to cellular work. Products are more stable and phosphorylation can alter the reactivity of another molecule." }, { "id": "molecules-atp-hydrolysis-integrated", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which paired outcome and explanation best follows from this condition: ATP is hydrolysed to ADP and inorganic phosphate?", "options": [ "Usable free energy can be coupled to cellular work — Products are more stable and phosphorylation can alter the reactivity of another molecule", "A lilac or purple colour develops — Copper ions form coloured complexes with peptide-bond nitrogens in alkaline conditions", "The blue reagent forms a green-to-brick-red precipitate depending on concentration — The sugar reduces copper(II) ions to insoluble copper(I) oxide", "They can spontaneously form sealed bilayers or vesicles — Hydrophilic heads face water while hydrophobic tails cluster away from it" ], "answer": 0, "explanation": "Usable free energy can be coupled to cellular work. Products are more stable and phosphorylation can alter the reactivity of another molecule." }, { "id": "molecules-reducing-sugar-test-outcome", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "A heated sample containing a reducing sugar is mixed with Benedict's reagent. Which outcome follows most directly?", "options": [ "A lilac or purple colour develops", "The blue reagent forms a green-to-brick-red precipitate depending on concentration", "They can spontaneously form sealed bilayers or vesicles", "Catalytic activity declines even if peptide bonds remain intact" ], "answer": 1, "explanation": "The blue reagent forms a green-to-brick-red precipitate depending on concentration. The sugar reduces copper(II) ions to insoluble copper(I) oxide." }, { "id": "molecules-reducing-sugar-test-cause", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which change most directly explains this observation: the blue reagent forms a green-to-brick-red precipitate depending on concentration?", "options": [ "A sample with many peptide bonds is treated with Biuret reagent", "Phospholipids are dispersed in water", "A heated sample containing a reducing sugar is mixed with Benedict's reagent", "Heat disrupts ionic bonds and hydrogen bonds in an enzyme" ], "answer": 2, "explanation": "The blue reagent forms a green-to-brick-red precipitate depending on concentration. The sugar reduces copper(II) ions to insoluble copper(I) oxide." }, { "id": "molecules-reducing-sugar-test-mechanism", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After a heated sample containing a reducing sugar is mixed with Benedict's reagent, which explanation best links the change to its outcome?", "options": [ "Copper ions form coloured complexes with peptide-bond nitrogens in alkaline conditions", "Hydrophilic heads face water while hydrophobic tails cluster away from it", "Loss of tertiary structure changes the geometry and chemistry of the active site", "The sugar reduces copper(II) ions to insoluble copper(I) oxide" ], "answer": 3, "explanation": "The blue reagent forms a green-to-brick-red precipitate depending on concentration. The sugar reduces copper(II) ions to insoluble copper(I) oxide." }, { "id": "molecules-reducing-sugar-test-integrated", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which paired outcome and explanation best follows from this condition: a heated sample containing a reducing sugar is mixed with Benedict's reagent?", "options": [ "The blue reagent forms a green-to-brick-red precipitate depending on concentration — The sugar reduces copper(II) ions to insoluble copper(I) oxide", "They can spontaneously form sealed bilayers or vesicles — Hydrophilic heads face water while hydrophobic tails cluster away from it", "Catalytic activity declines even if peptide bonds remain intact — Loss of tertiary structure changes the geometry and chemistry of the active site", "A lilac or purple colour develops — Copper ions form coloured complexes with peptide-bond nitrogens in alkaline conditions" ], "answer": 0, "explanation": "The blue reagent forms a green-to-brick-red precipitate depending on concentration. The sugar reduces copper(II) ions to insoluble copper(I) oxide." }, { "id": "molecules-biuret-test-outcome", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After a sample with many peptide bonds is treated with Biuret reagent, which observation is most likely?", "options": [ "They can spontaneously form sealed bilayers or vesicles", "A lilac or purple colour develops", "Catalytic activity declines even if peptide bonds remain intact", "The pH changes less than it would in pure water" ], "answer": 1, "explanation": "A lilac or purple colour develops. Copper ions form coloured complexes with peptide-bond nitrogens in alkaline conditions." }, { "id": "molecules-biuret-test-cause", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "A learner records that a lilac or purple colour develops. Which preceding event best accounts for it?", "options": [ "Phospholipids are dispersed in water", "Heat disrupts ionic bonds and hydrogen bonds in an enzyme", "A sample with many peptide bonds is treated with Biuret reagent", "A small amount of acid is added to a biological buffer" ], "answer": 2, "explanation": "A lilac or purple colour develops. Copper ions form coloured complexes with peptide-bond nitrogens in alkaline conditions." }, { "id": "molecules-biuret-test-mechanism", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "After a sample with many peptide bonds is treated with Biuret reagent, which explanation best links the change to its outcome?", "options": [ "Hydrophilic heads face water while hydrophobic tails cluster away from it", "Loss of tertiary structure changes the geometry and chemistry of the active site", "The buffer's conjugate base accepts much of the added hydrogen ions", "Copper ions form coloured complexes with peptide-bond nitrogens in alkaline conditions" ], "answer": 3, "explanation": "A lilac or purple colour develops. Copper ions form coloured complexes with peptide-bond nitrogens in alkaline conditions." }, { "id": "molecules-biuret-test-integrated", "chapter": "Biological Molecules", "difficulty": "Standard", "stem": "Which paired outcome and explanation best follows from this condition: a sample with many peptide bonds is treated with Biuret reagent?", "options": [ "A lilac or purple colour develops — Copper ions form coloured complexes with peptide-bond nitrogens in alkaline conditions", "They can spontaneously form sealed bilayers or vesicles — Hydrophilic heads face water while hydrophobic tails cluster away from it", "Catalytic activity declines even if peptide bonds remain intact — Loss of tertiary structure changes the geometry and chemistry of the active site", "The pH changes less than it would in pure water — The buffer's conjugate base accepts much of the added hydrogen ions" ], "answer": 0, "explanation": "A lilac or purple colour develops. Copper ions form coloured complexes with peptide-bond nitrogens in alkaline conditions." }, { "id": "molecules-phospholipid-vesicle-outcome", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "A student models this change: Phospholipids are dispersed in water. What should the model predict first?", "options": [ "Catalytic activity declines even if peptide bonds remain intact", "They can spontaneously form sealed bilayers or vesicles", "The pH changes less than it would in pure water", "The polymer separates into nucleotide components" ], "answer": 1, "explanation": "They can spontaneously form sealed bilayers or vesicles. Hydrophilic heads face water while hydrophobic tails cluster away from it." }, { "id": "molecules-phospholipid-vesicle-cause", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "What is the most likely cause when they can spontaneously form sealed bilayers or vesicles?", "options": [ "Heat disrupts ionic bonds and hydrogen bonds in an enzyme", "A small amount of acid is added to a biological buffer", "Phospholipids are dispersed in water", "Phosphodiester bonds in DNA are completely hydrolysed" ], "answer": 2, "explanation": "They can spontaneously form sealed bilayers or vesicles. Hydrophilic heads face water while hydrophobic tails cluster away from it." }, { "id": "molecules-phospholipid-vesicle-mechanism", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "After phospholipids are dispersed in water, which explanation best links the change to its outcome?", "options": [ "Cleavage breaks the covalent sugar-phosphate links between adjacent nucleotides", "Loss of tertiary structure changes the geometry and chemistry of the active site", "The buffer's conjugate base accepts much of the added hydrogen ions", "Hydrophilic heads face water while hydrophobic tails cluster away from it" ], "answer": 3, "explanation": "They can spontaneously form sealed bilayers or vesicles. Hydrophilic heads face water while hydrophobic tails cluster away from it." }, { "id": "molecules-enzyme-denaturation-outcome", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "Which immediate result is most consistent with this condition: Heat disrupts ionic bonds and hydrogen bonds in an enzyme?", "options": [ "Catalytic activity declines even if peptide bonds remain intact", "The polymer separates into nucleotide components", "Its complete oxidation generally yields more ATP", "The pH changes less than it would in pure water" ], "answer": 0, "explanation": "Catalytic activity declines even if peptide bonds remain intact. Loss of tertiary structure changes the geometry and chemistry of the active site." }, { "id": "molecules-enzyme-denaturation-cause", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "Which condition would most specifically produce this result: catalytic activity declines even if peptide bonds remain intact?", "options": [ "A small amount of acid is added to a biological buffer", "Heat disrupts ionic bonds and hydrogen bonds in an enzyme", "Phosphodiester bonds in DNA are completely hydrolysed", "A triglyceride contains longer and more reduced fatty-acid chains" ], "answer": 1, "explanation": "Catalytic activity declines even if peptide bonds remain intact. Loss of tertiary structure changes the geometry and chemistry of the active site." }, { "id": "molecules-enzyme-denaturation-mechanism", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "After heat disrupts ionic bonds and hydrogen bonds in an enzyme, which explanation best links the change to its outcome?", "options": [ "The buffer's conjugate base accepts much of the added hydrogen ions", "Cleavage breaks the covalent sugar-phosphate links between adjacent nucleotides", "Loss of tertiary structure changes the geometry and chemistry of the active site", "More carbon-hydrogen bonds supply additional electrons to respiratory carriers" ], "answer": 2, "explanation": "Catalytic activity declines even if peptide bonds remain intact. Loss of tertiary structure changes the geometry and chemistry of the active site." }, { "id": "molecules-enzyme-denaturation-integrated", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "Which paired outcome and explanation best follows from this condition: heat disrupts ionic bonds and hydrogen bonds in an enzyme?", "options": [ "The pH changes less than it would in pure water — The buffer's conjugate base accepts much of the added hydrogen ions", "The polymer separates into nucleotide components — Cleavage breaks the covalent sugar-phosphate links between adjacent nucleotides", "Its complete oxidation generally yields more ATP — More carbon-hydrogen bonds supply additional electrons to respiratory carriers", "Catalytic activity declines even if peptide bonds remain intact — Loss of tertiary structure changes the geometry and chemistry of the active site" ], "answer": 3, "explanation": "Catalytic activity declines even if peptide bonds remain intact. Loss of tertiary structure changes the geometry and chemistry of the active site." }, { "id": "molecules-buffer-action-outcome", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "A small amount of acid is added to a biological buffer. Which outcome follows most directly?", "options": [ "The pH changes less than it would in pure water", "The polymer separates into nucleotide components", "Its complete oxidation generally yields more ATP", "The protein may precipitate from solution" ], "answer": 0, "explanation": "The pH changes less than it would in pure water. The buffer's conjugate base accepts much of the added hydrogen ions." }, { "id": "molecules-buffer-action-cause", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "Which change most directly explains this observation: the pH changes less than it would in pure water?", "options": [ "Phosphodiester bonds in DNA are completely hydrolysed", "A small amount of acid is added to a biological buffer", "A triglyceride contains longer and more reduced fatty-acid chains", "A very high salt concentration surrounds a soluble protein" ], "answer": 1, "explanation": "The pH changes less than it would in pure water. The buffer's conjugate base accepts much of the added hydrogen ions." }, { "id": "molecules-buffer-action-mechanism", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "After a small amount of acid is added to a biological buffer, which explanation best links the change to its outcome?", "options": [ "Cleavage breaks the covalent sugar-phosphate links between adjacent nucleotides", "More carbon-hydrogen bonds supply additional electrons to respiratory carriers", "The buffer's conjugate base accepts much of the added hydrogen ions", "Ions compete for water and weaken the hydration shell around exposed protein groups" ], "answer": 2, "explanation": "The pH changes less than it would in pure water. The buffer's conjugate base accepts much of the added hydrogen ions." }, { "id": "molecules-buffer-action-integrated", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "Which paired outcome and explanation best follows from this condition: a small amount of acid is added to a biological buffer?", "options": [ "The polymer separates into nucleotide components — Cleavage breaks the covalent sugar-phosphate links between adjacent nucleotides", "Its complete oxidation generally yields more ATP — More carbon-hydrogen bonds supply additional electrons to respiratory carriers", "The protein may precipitate from solution — Ions compete for water and weaken the hydration shell around exposed protein groups", "The pH changes less than it would in pure water — The buffer's conjugate base accepts much of the added hydrogen ions" ], "answer": 3, "explanation": "The pH changes less than it would in pure water. The buffer's conjugate base accepts much of the added hydrogen ions." }, { "id": "molecules-dna-hydrolysis-outcome", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "After phosphodiester bonds in DNA are completely hydrolysed, which observation is most likely?", "options": [ "The polymer separates into nucleotide components", "Its complete oxidation generally yields more ATP", "The protein may precipitate from solution", "Water shows strong cohesion and a relatively high surface tension" ], "answer": 0, "explanation": "The polymer separates into nucleotide components. Cleavage breaks the covalent sugar-phosphate links between adjacent nucleotides." }, { "id": "molecules-dna-hydrolysis-cause", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "A learner records that the polymer separates into nucleotide components. Which preceding event best accounts for it?", "options": [ "A triglyceride contains longer and more reduced fatty-acid chains", "Phosphodiester bonds in DNA are completely hydrolysed", "A very high salt concentration surrounds a soluble protein", "Many hydrogen bonds form between neighbouring water molecules" ], "answer": 1, "explanation": "The polymer separates into nucleotide components. Cleavage breaks the covalent sugar-phosphate links between adjacent nucleotides." }, { "id": "molecules-dna-hydrolysis-mechanism", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "After phosphodiester bonds in DNA are completely hydrolysed, which explanation best links the change to its outcome?", "options": [ "More carbon-hydrogen bonds supply additional electrons to respiratory carriers", "Ions compete for water and weaken the hydration shell around exposed protein groups", "Cleavage breaks the covalent sugar-phosphate links between adjacent nucleotides", "Each weak hydrogen bond contributes to a large cooperative attraction in bulk water" ], "answer": 2, "explanation": "The polymer separates into nucleotide components. Cleavage breaks the covalent sugar-phosphate links between adjacent nucleotides." }, { "id": "molecules-dna-hydrolysis-integrated", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "Which paired outcome and explanation best follows from this condition: phosphodiester bonds in DNA are completely hydrolysed?", "options": [ "Water shows strong cohesion and a relatively high surface tension — Each weak hydrogen bond contributes to a large cooperative attraction in bulk water", "Its complete oxidation generally yields more ATP — More carbon-hydrogen bonds supply additional electrons to respiratory carriers", "The protein may precipitate from solution — Ions compete for water and weaken the hydration shell around exposed protein groups", "The polymer separates into nucleotide components — Cleavage breaks the covalent sugar-phosphate links between adjacent nucleotides" ], "answer": 3, "explanation": "The polymer separates into nucleotide components. Cleavage breaks the covalent sugar-phosphate links between adjacent nucleotides." }, { "id": "molecules-omega-oxidation-outcome", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "A student models this change: A triglyceride contains longer and more reduced fatty-acid chains. What should the model predict first?", "options": [ "Its complete oxidation generally yields more ATP", "Water shows strong cohesion and a relatively high surface tension", "The protein may precipitate from solution", "Its temperature rises more slowly than that of many other small molecules" ], "answer": 0, "explanation": "Its complete oxidation generally yields more ATP. More carbon-hydrogen bonds supply additional electrons to respiratory carriers." }, { "id": "molecules-omega-oxidation-cause", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "What is the most likely cause when its complete oxidation generally yields more ATP?", "options": [ "A very high salt concentration surrounds a soluble protein", "A triglyceride contains longer and more reduced fatty-acid chains", "Heat energy is added to liquid water", "Many hydrogen bonds form between neighbouring water molecules" ], "answer": 1, "explanation": "Its complete oxidation generally yields more ATP. More carbon-hydrogen bonds supply additional electrons to respiratory carriers." }, { "id": "molecules-omega-oxidation-mechanism", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "After a triglyceride contains longer and more reduced fatty-acid chains, which explanation best links the change to its outcome?", "options": [ "Each weak hydrogen bond contributes to a large cooperative attraction in bulk water", "Ions compete for water and weaken the hydration shell around exposed protein groups", "More carbon-hydrogen bonds supply additional electrons to respiratory carriers", "Much of the input energy first disrupts hydrogen-bond interactions" ], "answer": 2, "explanation": "Its complete oxidation generally yields more ATP. More carbon-hydrogen bonds supply additional electrons to respiratory carriers." }, { "id": "molecules-omega-oxidation-integrated", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "Which paired outcome and explanation best follows from this condition: a triglyceride contains longer and more reduced fatty-acid chains?", "options": [ "The protein may precipitate from solution — Ions compete for water and weaken the hydration shell around exposed protein groups", "Its temperature rises more slowly than that of many other small molecules — Much of the input energy first disrupts hydrogen-bond interactions", "Water shows strong cohesion and a relatively high surface tension — Each weak hydrogen bond contributes to a large cooperative attraction in bulk water", "Its complete oxidation generally yields more ATP — More carbon-hydrogen bonds supply additional electrons to respiratory carriers" ], "answer": 3, "explanation": "Its complete oxidation generally yields more ATP. More carbon-hydrogen bonds supply additional electrons to respiratory carriers." }, { "id": "molecules-protein-salting-outcome", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "Which immediate result is most consistent with this condition: A very high salt concentration surrounds a soluble protein?", "options": [ "The protein may precipitate from solution", "Its temperature rises more slowly than that of many other small molecules", "A disaccharide and one molecule of water are formed", "Water shows strong cohesion and a relatively high surface tension" ], "answer": 0, "explanation": "The protein may precipitate from solution. Ions compete for water and weaken the hydration shell around exposed protein groups." }, { "id": "molecules-protein-salting-cause", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "Which condition would most specifically produce this result: the protein may precipitate from solution?", "options": [ "Many hydrogen bonds form between neighbouring water molecules", "A very high salt concentration surrounds a soluble protein", "Heat energy is added to liquid water", "Two monosaccharides join by a condensation reaction" ], "answer": 1, "explanation": "The protein may precipitate from solution. Ions compete for water and weaken the hydration shell around exposed protein groups." }, { "id": "molecules-protein-salting-mechanism", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "After a very high salt concentration surrounds a soluble protein, which explanation best links the change to its outcome?", "options": [ "Each weak hydrogen bond contributes to a large cooperative attraction in bulk water", "Much of the input energy first disrupts hydrogen-bond interactions", "Ions compete for water and weaken the hydration shell around exposed protein groups", "A glycosidic bond forms as hydroxyl groups contribute hydrogen and hydroxyl" ], "answer": 2, "explanation": "The protein may precipitate from solution. Ions compete for water and weaken the hydration shell around exposed protein groups." }, { "id": "molecules-protein-salting-integrated", "chapter": "Biological Molecules", "difficulty": "Challenge", "stem": "Which paired outcome and explanation best follows from this condition: a very high salt concentration surrounds a soluble protein?", "options": [ "Water shows strong cohesion and a relatively high surface tension — Each weak hydrogen bond contributes to a large cooperative attraction in bulk water", "Its temperature rises more slowly than that of many other small molecules — Much of the input energy first disrupts hydrogen-bond interactions", "A disaccharide and one molecule of water are formed — A glycosidic bond forms as hydroxyl groups contribute hydrogen and hydroxyl", "The protein may precipitate from solution — Ions compete for water and weaken the hydration shell around exposed protein groups" ], "answer": 3, "explanation": "The protein may precipitate from solution. Ions compete for water and weaken the hydration shell around exposed protein groups." }, { "chapter": "Biological Molecules", "id": "applied-peptide-water", "difficulty": "Standard", "stem": "A linear peptide contains 12 amino acid residues. How many peptide bonds are present, and how many water molecules are used in its complete hydrolysis?", "options": [ "11 bonds; 11 waters", "12 bonds; 12 waters", "11 bonds; 12 waters", "12 bonds; 11 waters" ], "answer": 0, "explanation": "A linear chain of n amino acids has n − 1 peptide bonds. Hydrolysis consumes one water per bond, so both values are 11." }, { "chapter": "Biological Molecules", "id": "applied-dna-composition", "difficulty": "Standard", "stem": "In double-stranded DNA, adenine constitutes 28% of the bases. What percentage is cytosine?", "options": [ "28%", "22%", "44%", "14%" ], "answer": 1, "explanation": "A pairs with T, so A + T = 56%. The remaining 44% is split equally between G and C; cytosine is 22%." }, { "chapter": "Biological Molecules", "id": "applied-reducing-hydrolysis", "difficulty": "Challenge", "stem": "Which interpretation best explains these results for a purified carbohydrate solution?", "options": [ "Hydrolysis removes all carbohydrate", "It contains only free glucose before hydrolysis", "It contains a non-reducing carbohydrate that yields reducing products on hydrolysis", "It must be a protein" ], "answer": 2, "explanation": "A negative initial reducing-sugar test followed by a positive test after hydrolysis supports a non-reducing carbohydrate yielding reducing sugars. The data do not uniquely identify sucrose.", "visual": { "kind": "table", "caption": "Benedict’s test; equal aliquots heated with reagent", "headers": [ "Sample treatment", "Observation" ], "rows": [ [ "Before hydrolysis", "Remains blue" ], [ "After acid hydrolysis and neutralisation", "Orange precipitate" ] ] } }, { "chapter": "Biological Molecules", "id": "applied-membrane-fluidity", "difficulty": "Standard", "stem": "Two otherwise similar phospholipid mixtures differ only in fatty acid tails. Mixture P has more cis double bonds. At the same moderate temperature, P is expected to be:", "options": [ "More tightly packed and less fluid", "Unable to form a bilayer", "Covalently bonded into a rigid network", "Less tightly packed and more fluid" ], "answer": 3, "explanation": "Cis double bonds introduce bends that hinder close packing. This generally increases bilayer fluidity relative to more saturated tails under comparable conditions." } ] }