What is the function of the erector spinae?

Correct Answer: C

Rationale: Erector spinae, along the spine, extends and stabilizes it, providing postural support for standing and lifting. Arm movement involves deltoid or biceps. Pelvic stabilization uses gluteals or obliques. Rotation involves rotatores or obliques, not erector spinae's primary extension. Its role in maintaining upright posture distinguishes it, essential for spinal integrity, unlike arm, pelvic, or twisting functions.

Correct Answer: D

Rationale: Water's ability to mound above a glass rim results from surface tension, a property arising from cohesive forces between its molecules. Hydrogen bonds create a strong, elastic 'skin' at the surface, resisting external disruption and allowing water to hold together against gravity briefly. Specific gravity relates to density, not this behavior. Cohesion contributes but isn't the complete mechanism. Opacity, transparency-related, is irrelevant. Surface tension's role in forming this temporary barrier, driven by molecular attraction, explains the phenomenon, a key feature in water's physical behavior.

Correct Answer: C

Rationale: Acidity depends on ion concentration affecting pH. Hydronium ions (H₃O⁺), formed when protons (H⁺) bond with water, increase in acidic solutions, lowering pH below 7, as in vinegar. Hydroxyl ions (OH⁻) raise pH, making solutions basic. Sodium and potassium ions, from salts, are neutral, minimally shifting pH unless paired with strong acids or bases. Hydronium's direct link to proton donation defines acidity, distinguishing it in chemical equilibria and pH measurement.

Correct Answer: A

Rationale: The kidney filters blood and regulates fluid balance primarily through nephrons microscopic units numbering millions per kidney. Each nephron's glomerulus filters plasma, while tubules reabsorb water, glucose, and ions, and excrete waste as urine. Neurons conduct signals, ureters transport urine, and alveoli exchange lung gases. The nephron's integrated filtration, reabsorption, and secretion, occurring in structures like the loop of Henle, perform the kidney's core work, maintaining homeostasis and distinguishing it as the functional powerhouse.

Correct Answer: D

Rationale: Thin filaments comprise actin (structural backbone), troponin (Ca²⁺-binding regulator), and tropomyosin (site-covering protein), interacting with myosin for contraction. Myosin forms thick filaments, excluded from thin ones. Listing only troponin or tropomyosin omits actin's essential role thin filaments need all three. Actin alone misses regulatory components. The combination minus myosin defines thin filaments, enabling controlled actin-myosin binding, distinguishing it from partial or thick filament compositions, critical for sarcomere function.