The graph below shows the oxygen saturation profiles in counter-current and parallel flow exchange systems across the gill lamellae of fish.
According to Fick's Law:
Rate of Diffusion∝Surface Area×Difference in ConcentrationThickness of Membrane \text{Rate of Diffusion} \propto \frac{\text{Surface Area} \times \text{Difference in Concentration}}{\text{Thickness of Membrane}} Rate of Diffusion∝Thickness of MembraneSurface Area×Difference in ConcentrationWhich of the following options correctly matches a specialized exchange surface adaptation to its physiological consequence and the primary parameter of Fick's Law that it optimizes?
Adaptation: Counter-current flow of blood and water in bony fish gill lamellae.
Consequence: Water always meets blood with a lower oxygen partial pressure, maintaining a net diffusion gradient along the entire length of the lamellae.
Parameter optimized: Difference in concentration.
Adaptation: Secretion of phospholipid-protein surfactant in mammalian alveoli.
Consequence: Increases the surface tension of the fluid lining the alveoli, preventing them from collapsing during expiration.
Parameter optimized: Surface area.
Adaptation: Liquid-filled ends of insect tracheoles.
Consequence: Retaining high fluid volumes in the tracheoles during muscle contraction increases the rate of gas diffusion through the liquid phase.
Parameter optimized: Thickness of membrane.
Adaptation: Multi-layered (stratified) squamous epithelium in mammalian alveoli.
Consequence: Provides structural strength to resist high ventilation pressures while minimizing the overall diffusion path.
Parameter optimized: Thickness of membrane.