Suppose cube a is 10 cm along each edge and cube b is 5 cm along each edge. What is the relationship of the volume of cube a to that of cube b ?

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: 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.

Correct Answer: B

Rationale: Calcium's role is binding troponin, altering its shape to shift tropomyosin, exposing actin's binding sites for myosin. It doesn't propagate action potentials (acetylcholine does), bind myosin, or engage actin directly those involve ATP and cross-bridge mechanics. This troponin interaction regulates contraction, distinguishing it from nerve or energy roles, pivotal in the sliding filament process.