Hydrogen can be prepared in the lab by combining Zn and HCl; the resulting reaction is metallic zinc:

Correct Answer: C

Rationale: In the reaction Zn + 2HCl → ZnCl₂ + H₂, zinc displaces hydrogen from hydrochloric acid. Zinc atoms react with HCl, taking hydrogen's place to form zinc chloride, releasing hydrogen gas. This single displacement reaction doesn't transmute zinc into another element, nor does it primarily involve water or catalysis zinc is a reactant, not a catalyst. The replacement of hydrogen, driven by zinc's higher reactivity, produces hydrogen gas, a classic lab method, highlighting chemical reactivity and gas evolution principles.

Correct Answer: C

Rationale: The sarcoplasmic reticulum, a specialized endoplasmic reticulum, stores calcium ions (Ca²⁺) in muscle fibers, releasing them upon T-tubule signals to trigger contraction via troponin binding. T-tubules conduct action potentials, not storing Ca²⁺. Myofibrils, contractile units of actin and myosin, rely on Ca²⁺ but don't store it. Troponin binds Ca²⁺ to shift tropomyosin, not storing it its source is the reticulum. Sarcoplasmic reticulum's storage role ensures rapid, regulated Ca²⁺ availability, distinguishing it from conduction, contraction, or binding structures, critical for muscle activation.

Correct Answer: D

Rationale: Each myosin head uses one ATP molecule, hydrolyzed to ADP and phosphate, to change shape, cocking for the power stroke and detaching post-actin binding, fueling one cycle. Ca²⁺ binds troponin, not myosin, initiating exposure, not shape change. Two ADP or ATP molecules overstate biochemistry confirms one ATP per stroke. Na⁺ drives depolarization, not myosin mechanics. One ATP's energy distinguishes it, critical for efficient contraction, unlike ions or excess molecules.

Correct Answer: A

Rationale: Muscle names may reflect action, movement produced. Adductor longus indicates adduction drawing a limb toward the midline as its primary function, with longus denoting size. Temporalis refers to its temporal bone location, sternocleidomastoid to origin-insertion points, and peroneus longus to its fibular position and length. Only adductor directly names the action, a convention aiding functional understanding, distinguishing it from location- or attachment-based names, essential for predicting muscle roles in movement analysis.

Correct Answer: C

Rationale: Thin myofilaments, in sarcomeres, comprise actin, a structural protein forming the filament backbone, tropomyosin, which covers actin's binding sites, and troponin, which binds calcium to shift tropomyosin during contraction. Myosin forms thick myofilaments, not thin ones. This trio actin, tropomyosin, troponin enables regulated contraction, distinguishing thin filaments' composition and role from thick filaments, essential for the sliding filament theory of muscle action.