Which list is in the correct order of DECREASING size?

Correct Answer: B

Rationale: Size hierarchy: muscle (organ) contains fasciculi (fibre bundles), then muscle fibres (cells), then myofibrils (fibre-length). Sarcomeres (2 micrometres) and myofilaments are within myofibrils, myosin is molecular. Only 'muscle, fasciculus, fibre, myofibril' descends correctly, distinguishing organizational scale, key to muscle structure understanding.

Correct Answer: B

Rationale: Aerobic respiration is oxidative phosphorylation in mitochondria, using oxygen to generate ATP from pyruvate, yielding high energy for sustained effort. Glycolysis is anaerobic or preparatory, gluconeogenesis synthesizes glucose. This oxygen-dependent process distinguishes it, key to endurance muscle energy, contrasting with anaerobic pathways.

Correct Answer: A

Rationale: A synergist assists an agonist (prime mover) by contracting to support or enhance its action, reducing unwanted movement or adding force, like the brachioradialis aiding the biceps brachii in elbow flexion. A fixator stabilizes a bone or joint (e.g., shoulder girdle muscles during arm movement), not directly helping the agonist's motion. An insertion is the muscle's movable attachment point, not a helper type. An antagonist opposes the agonist (e.g., triceps brachii vs. biceps), hindering, not aiding. Synergists' cooperative role in muscle mechanics, refining agonist efficiency, makes 'a' the correct choice.

Correct Answer: C

Rationale: The sternocleidomastoid (SCM) is a prime mover in head flexion, contracting bilaterally to bend the neck forward, originating from the sternum/clavicle and inserting on the mastoid process. Occipitofrontalis raises eyebrows and wrinkles the forehead, not flexing the head. Corrugator supercilii furrows brows, a facial expression muscle. Masseter elevates the mandible for chewing, not head flexion. SCM's powerful, direct action on cervical flexion, a key neck movement, makes 'c' the correct prime mover.

Correct Answer: A

Rationale: The pectoral girdle (shoulder girdle) is stabilized by axial muscles (e.g., trapezius, connecting spine to scapula) and scapular muscles (e.g., rhomboids, serratus anterior, anchoring scapula), balancing mobility and stability. Axial alone omits scapular contribution. Appendicular includes limb muscles, not all girdle stabilizers. Axial and appendicular overgeneralizes, as not all appendicular muscles stabilize the girdle. 'Axial and scapular' precisely identifies the stabilizing groups, making it correct.