Which muscles stabilize the pectoral girdle?

Correct Answer: A

Rationale: Axial (e.g., serratus anterior) and scapular (e.g., trapezius, rhomboids) muscles stabilize the pectoral girdle (scapula, clavicle). Axial alone omits scapular roles. Appendicular includes limb movers, not all stabilizers. Combining both captures serratus anchoring scapula to ribs and trapezius/rhomboids positioning it, distinguishing them, vital for shoulder stability.

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: D

Rationale: Bees and butterflies are vital pollinators, transferring pollen between flowers to enable fertilization and seed production in plants like fruits and vegetables. Their absence halts pollination, reducing seed output, as many plants can't self-pollinate effectively. Birds may rely on seeds, but their food need isn't the direct issue. More flowers or seeds contradict pollination's loss. Fewer seeds, a direct consequence, impacts ecosystems and agriculture, highlighting pollinators' critical role in reproduction.

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.