The primary force responsible for the movement of air into the lungs during inspiration?

Correct Answer: D

Rationale: Inspiration relies on Boyle's law: expanding the thorax lowers intrapulmonary pressure (e.g., 760 to 758 mmHg) below atmospheric, creating a pressure difference driving air in. Diaphragm and intercostal contraction generate this ~1-2 mmHg gradient for tidal breathing (~500 ml). Atmospheric pressure (760 mmHg) is static, not a force its difference with intrapulmonary pressure matters. Muscular spasm implies involuntary action, unlike controlled respiratory muscle contraction. Reduced surface tension (via surfactant) eases expansion but isn't the force pressure difference is. Muscle relaxation drives expiration, not inspiration. This gradient, directly linking mechanics to airflow, is the primary force, quantifiable and fundamental to ventilation, distinguishing it from secondary factors like surfactant or muscle state.

Correct Answer: A

Rationale: During mild exercise, gas exchange meets increased O2 demand and CO2 output. CO2 diffuses ~20 times faster than O2 across the alveolar-capillary membrane due to higher solubility (0.51 vs. 0.024 ml/mmHg/L), despite molecular weight (44 vs. 32), per Fick's law (D ∝ solubility / √MW) true. Diffusing capacity (DL) for O2 is less than CO2's; exercise boosts both via capillary recruitment, but solubility, not weight, drives CO2's edge false. Capillary equilibrium length may shorten with faster flow, but this is nuanced, not definitive false. Arterial blood gases (ABGs) stay normal (PaO2 ~100 mmHg, PaCO2 ~40 mmHg) in health during mild exercise false. CO2's easier diffusion, rooted in solubility, ensures rapid CO2 clearance, a key truth distinguishing gas exchange dynamics in exercise physiology.

Correct Answer: B

Rationale: Initial: VT = 1000 ml, VD = 200 ml, RR = 20/min. VE = VT × RR = 1000 × 20 = 20 L/min; VA = (VT - VD) × RR = (1000 - 200) × 20 = 16 L/min. T: VT = 2000 ml, RR = 10/min; VE = 2000 × 10 = 20 L/min (constant), VA = (2000 - 200) × 10 = 18 L/min (increases). V: VT = 500 ml, RR = 40/min; VE = 500 × 40 = 20 L/min (constant), VA = (500 - 200) × 40 = 12 L/min (decreases). T's higher VT boosts VA despite lower RR; V's lower VT cuts VA as dead space dominates. Option B (T: VE constant, VA increases; V: VE constant, VA decreases) fits, showing VT's impact on alveolar efficiency at fixed VE.

Correct Answer: B

Rationale: Evaporation from oceans is the primary source of atmospheric water vapor, contributing ~86% of global input (~400,000 km³/year), due to oceans' vast surface (~71% of Earth) and solar-driven evaporation. Transpiration from plants adds ~10% (~50,000 km³/year), significant but secondary. Sublimation of ice is minor, limited by polar cold and area. Volcanic eruptions inject water vapor (~1% of total), but episodically. Oceans' dominance, per hydrologic cycle data (e.g., Trenberth), drives humidity, clouds, and precipitation, with ~90% of atmospheric vapor (1.3×10¹³ m³) cycling through evaporation, making it the key source, far exceeding terrestrial or geological inputs.

Correct Answer: C

Rationale: The quadrangular membrane is a fibroelastic layer in the larynx, intrinsic (B), spanning from the epiglottis to arytenoids. Its upper margin forms aryepiglottic folds (A), and its lower margin thickens into vestibular (false) folds (D). Innervation (C) is sensory via the internal laryngeal nerve (above cords), not the recurrent laryngeal nerve, which supplies muscles below (e.g., vocalis). C is the exception recurrent laryngeal doesn't innervate this membrane.