The vastus intermedius muscle is deep to which of the following muscles?

Correct Answer: B

Rationale: Vastus intermedius, a quadriceps muscle, lies deep to rectus femoris, which overlays it on the anterior thigh, both extending the knee. Biceps femoris, a hamstring, is posterior. Vastus medialis and lateralis flank it laterally and medially, not superiorly. Rectus femoris' superficial position distinguishes it, key for quadriceps layering.

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.

Correct Answer: A

Rationale: Muscle cell components have specialized roles. The sarcolemma is the plasma membrane, sarcoplasm the cytoplasm, and sarcoplasmic reticulum a calcium-storing organelle all integral to muscle function. Sarcoma, however, denotes a connective tissue cancer, not a cellular structure, unrelated to normal muscle anatomy. This distinction matters: muscle-specific terms prefix sarco for flesh, but sarcoma's pathological context excludes it from healthy cell anatomy, unlike the others, which enable contraction and signal transduction in skeletal muscle fibres.