How many cranial bones are there?

Correct Answer: C

Rationale: Eight cranial bones form the skull's braincase: frontal, 2 parietals, 2 temporals, occipital, sphenoid, ethmoid. Options 10, 12, 14 (a, b, d) may confuse with facial bones (14 total), but cranial-specific is 8. This count, per skull anatomy, makes 'c' correct.

Correct Answer: C

Rationale: Hyaline cartilage, smooth and glassy, forms costal cartilage in the rib cage, connecting ribs to sternum, flexible yet supportive. Elastic is in ears, fibrocartilage in discs neither fit ribs. Hyaline's prevalence, per thorax, makes 'c' correct.

Correct Answer: C

Rationale: ATP stores energy in its phosphate bonds, releasing it controllably for cellular work (e.g., muscle contraction), a universal energy currency. It results from catabolism , but that's not why it's important storage is key. It doesn't release energy uncontrollably , that's inefficient. Not all only 'c' fits. ATP's energy storage role, per biochemistry, makes 'c' correct.

Correct Answer: D

Rationale: The lumbar region (lower back) is superior to the popliteal region (behind the knee), per anatomical regions lumbar above, popliteal lower on the leg. It's superior to gluteal , superior to umbilical , inferior to cervical . Superiority to popliteal, per body mapping, makes 'd' correct.

Correct Answer: A

Rationale: Thick myofilaments in sarcomeres are primarily myosin, a motor protein with a tail forming the filament backbone and heads projecting outward for actin binding. This structure, assembled from hundreds of myosin molecules, drives contraction via ATP-powered cross-bridge cycling. Thin filaments, conversely, comprise actin (a globular protein polymerized into strands), troponin (calcium-binding regulator), and tropomyosin (actin-covering modulator), not thick filaments. Combining myosin with troponin and tropomyosin lacks biochemical basis, as these regulate thin filaments. Actin alone forms thin filaments, not thick ones, and pairing myosin with actin misrepresents filament distinction. Myosin's unique tail-head configuration, detailed in structural biology, enables its role in force generation, distinct from thin filaments' regulatory proteins. Electron microscopy and X-ray diffraction reveal thick filaments as myosin aggregates, with heads engaging actin during contraction. This composition underpins muscle mechanics, ensuring thick filaments' contractile power, a fundamental concept in physiology distinguishing filament types.