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← Nature & AnimalsWhich factor most decreases the surface area for gas exchange if a fish's secondary lamellae fuse together?
A)Reduced haemoglobin concentration
B)Increased boundary layer thickness
C)Decreased countercurrent efficiency✓
D)Elevated blood flow velocity
💡 Explanation
When lamellae fuse, it diminishes the diffusion gradient because countercurrent exchange cannot efficiently occur because the opposing flow is disrupted. Therefore, countercurrent efficiency decreases, rather than layer thickness, flow velocity or haemoglobin since lamellae structural integrity affects the diffusion mechanics .
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