What are the components of the Gram-negative bacterial cell wall called?

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: 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.

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.