A 5-year-old and her father each lifted identical chairs from the floor to a tabletop. Which person did the most work?

Correct Answer: C

Rationale: Work in physics is force times distance. Both lifted identical chairs the same vertical distance, applying equal force against gravity (the chair's weight). Age or strength doesn't alter the chair's mass or height moved, so work done is identical. Without data on differing distances or forces like lifting speed or extra effort both perform equal work. This reflects work's definition, focusing on displacement and force, not individual capacity, making their efforts mechanically equivalent.

Correct Answer: D

Rationale: Thick filaments in sarcomeres are composed of myosin, with heads forming cross-bridges to pull actin during contraction, creating the A band's density. Troponin and tropomyosin, regulatory proteins, pair with actin in thin filaments, not thick. Actin forms thin filaments, overlapping myosin, not constituting thick ones. Myosin's exclusive role in thick filaments drives force generation, distinguishing it from thin filament components, fundamental to muscle contraction mechanics.

Correct Answer: C

Rationale: Muscle names often reflect origin (fixed attachment) and insertion (movable end). Sternocleidomastoid specifies origins on the sternum and clavicle, inserting on the mastoid process of the temporal bone, guiding neck movement. Transversus abdominus denotes fibre direction and location, semimembranosus' implies membrane-like shape and location, and deltoid reflects its triangular shape. Only sternocleidomastoid explicitly ties to origin-insertion points, a naming style aiding anatomical precision, distinguishing it from shape-, action-, or location-based names in functional mapping.

Correct Answer: B

Rationale: Within myofibrils, sarcomeres are the contractile units, shortening as actin and myosin slide past each other, powered by ATP. Sarcoplasm is cytoplasm, sarcolemma the membrane, and sarcoplasmic reticulum a calcium store not contractile. Sarcomeres' banded structure, from Z-line to Z-line, enables muscle contraction, their collective action summing to fibre shortening, distinguishing them as the functional core of myofibril mechanics in muscle physiology.

Correct Answer: B

Rationale: Skeletal muscle exhibits excitability (signal response), contractility (shortening), and extensibility (stretching), but is innervated by the somatic nervous system for voluntary control, not the autonomic system, which governs involuntary smooth and cardiac muscles. This voluntary innervation distinguishes skeletal muscle's conscious movement role e.g., lifting from autonomic-regulated visceral functions, key to its physiological classification.