The solubility of a solid in a liquid generally increases with:

Correct Answer: A

Rationale: Solubility of most solids in liquids rises with temperature because higher thermal energy enhances molecular motion, breaking solute-solute bonds and increasing solvent-solute interactions. For example, sugar dissolves better in hot water. Pressure affects gases more than solids, and decreasing temperature typically reduces solubility, as seen in crystallization. Lower pressure has minimal impact. This temperature-driven solubility increase, rooted in thermodynamics, applies broadly to ionic and polar solids, distinguishing it from gas solubility dynamics.

Correct Answer: D

Rationale: Acetylcholine (Ach), released by somatic motor neurons, excites skeletal muscle fibers by binding nicotinic receptors, opening Na⁺ channels to depolarize the sarcolemma, initiating contraction. GABA, inhibitory in the CNS, doesn't excite muscle. Na⁺ is an ion, not a neurotransmitter it enters post-Ach binding. Ca²⁺ triggers contraction internally, not as a neurotransmitter. Ach's excitatory role at the neuromuscular junction distinguishes it, key for signal transmission, unlike inhibitory, ionic, or intracellular agents.

Correct Answer: D

Rationale: Muscle names encode specific traits. Quadriceps femoris combines quadriceps, indicating four origins four distinct attachment points on the pelvis or femur with femoris, pinpointing its location on the thigh's femur bone. Action (e.g., extension) isn't specified, nor are insertion points (tibia via patella) or fibre direction (e.g., rectus). Location and origin count align with naming conventions, as seen in biceps or triceps, where number denotes origins and the second term locates it. This reflects skeletal muscle nomenclature's focus on anatomical anchors, distinguishing it from action-based or directional terms, crucial for identifying muscles in clinical and educational contexts.

Correct Answer: D

Rationale: Contraction begins with a neural signal. Calcium release from the sarcoplasmic reticulum into the cytoplasm is the first intracellular step, triggered by sarcolemma depolarization. This calcium binds troponin, exposing actin sites, followed by ATP binding and hydrolysis to drive myosin movement. ADP detachment occurs later in the cycle. Calcium's release initiates the cascade, distinct from subsequent biochemical steps, ensuring contraction aligns with nerve input, a critical sequence in muscle physiology.

Correct Answer: A

Rationale: Biceps brachii encodes two origins ( bi- ) two tendon heads on the scapula and location ( brachii ) on the arm's humerus. Action (flexion) isn't specified, nor is size (e.g., maximus) or shape (e.g., deltoid). This origin-location naming, common in muscles like triceps, aids anatomical mapping, distinguishing it from action- or shape-based names, reflecting skeletal muscle's attachment-based classification.