Which of these biological processes includes the other three?

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: 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.

Correct Answer: C

Rationale: Muscle roles define movement dynamics. An antagonist opposes or reverses an agonist's action, relaxing during the agonist's contraction e.g., triceps antagonize biceps in elbow flexion. Agonists drive the primary motion, synergists assist, and fixators stabilize. The antagonist's counteraction ensures controlled, reversible movements, a key biomechanical principle distinguishing it from supportive or driving roles, essential for coordinated skeletal motion.

Correct Answer: D

Rationale: Sustained activity beyond 30-40 minutes relies on aerobic respiration in mitochondria, oxidizing pyruvate (from glycolysis) with oxygen to produce 36-38 ATP per glucose far more than stored ATP (seconds), glycolysis (minutes), or creatine phosphate (15 seconds). This efficient, oxygen-dependent process supports endurance, distinguishing it from short-burst energy sources, critical for prolonged muscle function in activities like running.