The absorption of Na in ascending Loop of Henle:

Correct Answer: D

Rationale: Na absorption in ascending Loop is active in thick (Na /K /2Cl⁻ cotransport) and passive in thin (e.g., gradient-driven). All passive ignores thick's pump false. All active overstates thin incorrect. Reversed activity misaligns thick is active. Dual mechanism distinguishes it, critical for concentration gradient, unlike uniform or swapped errors.

Correct Answer: C

Rationale: H binds HCO₃⁻ first forms H₂CO₃, then splits to CO₂/H₂O (e.g., buffering sequence). H₂CO₃ to CO₂ is second not initial. HCO₃⁻ to H₂CO₃ reverses H drives. All in order missequences false. Binding start distinguishes it, critical for buffer mechanics, unlike subsequent or reversed steps.

Correct Answer: B

Rationale: The nephron (filtration to urine formation) is the kidney's functional unit not glomerulus (filtration site), ureter (transport), or Bowman's capsule (nephron part). This identifies the kidney's workhorse, critical for physiology, contrasting with its parts.

Correct Answer: B

Rationale: The loop of Henle concentrates urine via water (descending) and Na+ (ascending) reabsorption not filtration (glomerulus), hormones (endocrine), or digestion (gut). This defines its role, key for osmolarity, contrasting with other functions.

Correct Answer: A

Rationale: UTIs are bacterial (E. coli common) not viral, fungal (rare), or dietary. This identifies primary cause, key for treatment, contrasting with less common etiologies.