Which of the following statements regarding potential energy profiles in chemical reactions are correct?
Statement I: If potential energy of product P is lower than substrate S, the reaction is exothermic. Statement II: In exothermic reactions, external energy input is not required to form products. Statement III: Both exothermic and endothermic reactions must proceed through a higher potential energy transition state. Statement IV: Intermediate structural states between substrate and product are stable and long-lived.
Statement IV is incorrect because intermediate transition states are unstable and short-lived. Statements I, II, and III correctly describe reaction energy profiles.
Question 72 of 100
📘 CLASS XI
Which of the following statements regarding induced fit and catalytic cycle steps are correct?
Statement I: Substrate binding induces the enzyme to alter its shape, fitting more tightly around the substrate. Statement II: The active site breaks or forms chemical bonds to generate an enzyme-product (EP) complex. Statement III: Upon product release, the free enzyme is ready to enter another catalytic cycle. Statement IV: The enzyme is permanently destroyed during bond cleavage and cannot be reused.
Statement IV is incorrect because the enzyme is released unchanged after catalysis and can participate in repeated catalytic cycles. Statements I, II, and III accurately describe the catalytic cycle.
Question 73 of 100
📘 CLASS XI
Which of the following statements regarding temperature, pH, and substrate saturation kinetics are correct?
Statement I: Enzyme activity shows maximum velocity at optimum pH and optimum temperature. Statement II: Low temperature preserves enzymes in a temporarily inactive state, while high temperature denatures proteins. Statement III: Reaction velocity increases with substrate concentration until maximum velocity (Vmax) is reached. Statement IV: At substrate saturation, adding more substrate increases velocity beyond Vmax indefinitely.
Statement IV is incorrect because once all enzyme active sites are saturated, adding additional substrate cannot increase velocity beyond Vmax. Statements I, II, and III correctly describe enzyme kinetics.
Question 74 of 100
📘 CLASS XI
Which of the following statements regarding competitive inhibition and the malonate mechanism are correct?
Statement I: Competitive inhibitors closely resemble the substrate in molecular structure and compete for active site binding. Statement II: Inhibition of succinic dehydrogenase by malonate is a classic example of competitive inhibition. Statement III: Malonate closely resembles the substrate succinate in structure. Statement IV: Competitive inhibitors permanently destroy the apoenzyme's primary sequence.
Statement IV is incorrect because competitive inhibitors bind reversibly at the active site without destroying the primary protein sequence. Statements I, II, and III accurately describe competitive inhibition.
Question 75 of 100
📘 CLASS XI
Which of the following statements regarding EC enzyme classes (Class 1 to Class 6) are correct?
Statement I: Enzymes are divided into 6 classes, each with 4–13 subclasses, designated by a four-digit number. Statement II: Oxidoreductases catalyze oxidoreduction between two substrates. Statement III: Transferases catalyze group transfer (G) other than hydrogen between substrates. Statement IV: Hydrolases catalyze group removal leaving double bonds without water involvement.
Statement IV is incorrect because group removal leaving double bonds is catalyzed by Lyases, whereas Hydrolases catalyze bond cleavage by hydrolysis. Statements I, II, and III accurately summarize enzyme classification.
Question 76 of 100
📘 CLASS XI
Which of the following statements regarding the chemical analysis of living tissues and acid fractions are correct?
Statement I: When living tissue is ground in trichloroacetic acid and strained, the filtrate represents the acid-soluble pool while the retentate represents the acid-insoluble fraction. Statement II: Compounds in the acid-soluble pool have molecular weights ranging from 18 to around 800 Daltons. Statement III: The acid-insoluble fraction contains four types of organic compounds: proteins, nucleic acids, polysaccharides, and lipids. Statement IV: Lipids are true biomacromolecules with molecular weights strictly exceeding 10,000 Daltons.
Statement IV is incorrect because lipids have molecular weights not exceeding 800 Daltons and are not true macromolecules despite occurring in the acid-insoluble fraction due to vesicle formation. Statements I, II, and III are correct.
Question 77 of 100
📘 CLASS XI
Which of the following statements regarding primary vs. secondary metabolites are correct?
Statement I: Primary metabolites have identifiable physiological functions and direct roles in normal metabolic processes. Statement II: Secondary metabolites are produced in plant, fungal, and microbial cells and include alkaloids, flavonoids, rubber, and essential oils. Statement III: Morphine and codeine are secondary metabolites categorized as essential oils. Statement IV: Concanavalin A is a lectin, whereas abrin and ricin are toxins.
Statement III is incorrect because morphine and codeine are alkaloids, whereas lemon grass oil is an essential oil. Statements I, II, and IV correctly summarize NCERT Table 9.3.
Question 78 of 100
📘 CLASS XI
Which of the following statements regarding protein structural organization are correct?
Statement I: Primary structure of a protein describes the specific linear sequence of amino acids linked by peptide bonds. Statement II: The first amino acid at the left end is the N-terminal amino acid, and the last amino acid at the right end is the C-terminal amino acid. Statement III: In proteins, only right-handed helices are observed in secondary structure. Statement IV: Tertiary structure is a 3-dimensional folding required for the biological activity of enzymes.
All four statements are factually accurate according to NCERT. Primary sequence directionality is N-to-C terminal (left-to-right), secondary helices are right-handed, and tertiary structure is essential for biological activity.
Question 79 of 100
📘 CLASS XI
Which of the following statements regarding B-DNA structural geometry are correct?
Statement I: B-DNA consists of two polynucleotide strands running antiparallel to each other. Statement II: Adenine forms two hydrogen bonds with Thymine, and Guanine forms three hydrogen bonds with Cytosine. Statement III: The pitch of the B-DNA double helix is 3.4 nm and contains 10 base pairs per turn. Statement IV: The distance between two adjacent base pairs in B-DNA is 34 nm.
Statement IV is incorrect because the distance between adjacent base pairs is 0.34 nm (3.4 Å), not 34 nm. Statements I, II, and III correctly describe Watson-Crick B-DNA geometry.
Question 80 of 100
📘 CLASS XI
Which of the following statements regarding enzyme active sites and transition states are correct?
Statement I: The active site of an enzyme is a crevice created by the folding of its tertiary structure. Statement II: Substrate binding to the active site forms a transient enzyme-substrate (ES) complex. Statement III: The transition state structure formed during catalysis is a stable, long-lived energy state. Statement IV: Activation energy is the energy difference between the average energy level of the substrate and the transition state.
Statement III is incorrect because the transition state is highly unstable and transient. Statements I, II, and IV accurately describe active sites and activation energy.
