An excess of which of these ions tends to make a solution acidic?

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: 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.

Correct Answer: A

Rationale: Muscle fibres contain hierarchical structures. Myofibrils, bundles of sarcomeres, span the fibre's length (tens to hundreds of micrometres), housing myofilaments actin and myosin arrays within sarcomeres. Myosin is a protein molecule, and myopic is unrelated (likely a typo). Myofibrils, as the largest organized unit within the cell, integrate sarcomeres for contraction, distinguishing them from shorter myofilaments or molecular components, critical for muscle's macroscopic force generation.

Correct Answer: A

Rationale: Gluteus maximus denotes size maximus means largest relative to gluteus medius and minimus, all on the buttocks. Shape (e.g., trapezius), action (e.g., adductor), and origin-insertion (e.g., sternocleidomastoid) aren't specified. Its large mass aids hip extension, but size defines the name, distinguishing it in gluteal anatomy, reflecting naming conventions prioritizing relative scale.