The rhomboid major and minor muscles are deep to the

Correct Answer: C

Rationale: Rhomboid major and minor, retracting the scapula, lie deep to trapezius, a superficial back muscle covering them. Rectus abdominis is anterior, abdominal. Scalenes are in the neck, unrelated. Ligamentum nuchae, a neck ligament, aligns with deeper muscles but not rhomboids' position. Trapezius' superficiality over rhomboids distinguishes it, key for back layering.

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: D

Rationale: Volume of a cube is edge length cubed. Cube A (10 cm) has a volume of 10 × 10 × 10 = 1000 cm³; Cube B (5 cm) is 5 × 5 × 5 = 125 cm³. Dividing 1000 by 125 yields 8, meaning Cube A's volume is 8 times Cube B's. The edge ratio (10/5 = 2) cubes to 2³ = 8, confirming this. Options 2x, 4x, and 6x miscalculate the exponential relationship, making 8x the correct volumetric comparison.

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.