Which of the following is unique to the muscles of facial expression?

Correct Answer: D

Rationale: Facial expression muscles, like orbicularis oris or zygomaticus, uniquely insert into the skin, allowing fine movements like smiling or frowning, unlike skeletal muscles attaching to bones via tendons. They don't all originate from the scalp many arise from facial bones (e.g., zygomaticus from zygomatic bone). Cartilage insertions are rare and incorrect facial cartilage (e.g., nasal) isn't a primary target. Insertion solely onto facial bones applies to some but not all (e.g., masseter), missing the skin's role. Skin insertion enables their role in subtle, dynamic expressions, distinguishing them from scalp-origin, cartilage, or bone-only attachments, key to facial muscle function.

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: A

Rationale: Gram-negative bacteria possess a unique cell wall with an outer membrane containing lipopolysaccharides (LPS). These LPS molecules, termed endotoxins, are integral structural components released upon cell damage or death, triggering strong immune responses like fever or septic shock. Exotoxins are secreted proteins, not wall components, and 'toxins' is too vague. 'None of the above' ignores LPS's role. Endotoxins' presence in the gram-negative wall, distinct from gram-positive peptidoglycan, and their release mechanism underline their identity as key immunological triggers, differentiating them from secreted toxins.

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.