Which of these substances has the highest boiling point?

Correct Answer: D

Rationale: Boiling points depend on intermolecular forces. Glycerol, with three hydroxyl groups, forms extensive hydrogen bonds, requiring more energy to vaporize, yielding a boiling point of 290°C. Water (100°C) has strong hydrogen bonding but fewer sites per molecule. Ethanol (78°C) has one hydroxyl, and ether (34.6°C) relies on weaker dipole forces. Glycerol's multiple bonding sites create stronger attractions, elevating its boiling point, a key factor in its use in high-temperature applications, distinguishing it from less bonded compounds.

Correct Answer: C

Rationale: A cholinergic receptor, specifically the nicotinic subtype, on the muscle fiber's sarcolemma binds acetylcholine, opening Na⁺ channels to depolarize and contract the muscle. Adrenergic receptors (alpha/beta) bind catecholamines (e.g., norepinephrine) in smooth muscle or cardiac contexts, not skeletal. Beta receptors, a subset, are irrelevant here. Tyrosine kinase receptors (e.g., for growth factors) don't mediate neurotransmitter action. Cholinergic receptors' specificity for acetylcholine distinguishes them, critical for skeletal muscle excitation, unlike adrenergic or signaling receptors.

Correct Answer: D

Rationale: In muscle cells, specialized terminology distinguishes structures. The plasma membrane, enveloping the cell, is the sarcolemma sarco meaning flesh, lemma a sheath serving as the boundary for nerve signal transmission and ion exchange. Sarcoplasm is the cytoplasm, sarcomeres are contractile units within myofibrils, and the sarcoplasmic reticulum stores calcium. The sarcolemma's role in action potential propagation, via T-tubules, initiates contraction, setting it apart from internal components. This unique naming reflects muscle cells' adaptation for rapid, coordinated responses, essential in physiology for understanding excitation-contraction coupling.

Correct Answer: C

Rationale: A sarcomere is the contractile unit of muscle, a segment of a myofibril between Z-lines, containing overlapping actin and myosin myofilaments. It's not a cancer (sarcoma), cytoplasm (sarcoplasm), or membrane (sarcolemma), but a structural section where sliding filaments shorten during contraction. Defining myofibril organization, sarcomeres' repetitive nature enables muscle shortening, distinguishing them from pathological or cellular envelope terms, central to understanding muscle mechanics at the microscopic level.

Correct Answer: A

Rationale: The deltoid, in the upper arm's shoulder region, is a standard intramuscular injection site due to its accessible, thick muscle mass, minimizing nerve damage risk. Gluteus maximus is avoided to protect the sciatic nerve (gluteus medius is preferred), vastus medialis isn't typical, and latissimus dorsi, on the back, lacks suitable mass and access. Deltoid's prominence and safety distinguish it in clinical practice, key for effective drug delivery.