Which muscle produces movement that allows you to cross your legs?

Correct Answer: D

Rationale: Sartorius, a long, strap-like muscle, flexes, abducts, and laterally rotates the hip, then flexes the knee, enabling leg crossing. Gluteus maximus extends the hip. Piriformis rotates it. Gracilis adducts, not crossing fully. Sartorius' multi-joint action distinguishes it, critical for this coordinated motion.

Correct Answer: A

Rationale: Cellular respiration encompasses the breakdown of glucose to produce ATP, involving glycolysis, the Krebs cycle, and the electron transport chain. Glycolysis includes anaerobic glucose splitting, yielding pyruvate, which feeds the Krebs cycle under aerobic conditions. The Krebs cycle generates electron carriers, fueling the electron transport chain for ATP synthesis. Anaerobic splitting is a subset when oxygen is absent. Cellular respiration's integration of these stages, converting food to energy, makes it the overarching process, central to cellular metabolism across organisms.

Correct Answer: C

Rationale: Most bacteria thrive at 37°C (98.6°F), mimicking human body temperature, ideal for pathogens like E. coli in lab cultures. An incubator maintains this stable warmth, promoting growth. A lighted window (22°C) varies and is cooler, a refrigerator (7°C) slows metabolism, and a freezer (-12°C) halts it. The incubator's optimal temperature, matching bacterial physiology, ensures rapid division and colony formation, making it the best choice for cultivating diverse species.

Correct Answer: C

Rationale: Tropomyosin moves off actin's myosin-binding sites when Ca²⁺ binds troponin, which shifts tropomyosin, allowing myosin to bind actin for contraction. Ca²⁺ and troponin don't move off they enable the shift. Troponin doesn't block sites or move myosin it's regulatory. Troponin moving tropomyosin reverses roles tropomyosin shifts due to troponin. Tropomyosin's displacement by troponin-Ca²⁺ distinguishes it, key to exposing sites, unlike static or reversed pairings, central to sliding filament theory.

Correct Answer: A

Rationale: Smooth and skeletal muscles differ structurally and functionally. Smooth muscle lines artery walls, enabling involuntary constriction to regulate blood flow, unlike skeletal muscle, which attaches to bones for voluntary movement. Skeletal muscle is multinucleate and striated, lacking intercalated discs features of cardiac muscle not smooth muscle, which is uninucleate and non-striated. Smooth muscle's presence in visceral organs, controlled by the autonomic nervous system, contrasts with skeletal muscle's somatic control, highlighting its role in automatic processes like circulation, distinct from skeletal muscle's locomotive purpose.