For gas exchange to be effective the area for gas diffusion needs to have a high surface area to volume ratio as well as a short diffusion pathway, e.g. the alveoli are only one cell thick.
Gas Exchange in Fish
The gas exhange organs in the fish are the gills which are loacted between the mouth cavity and ther operculum. Fish remove oxygen from the water by pushing the water through the gill filaments, after it enters the mouth. These filaments have a huge surface area compared to volume due to the lamellae which are at right angles to the filaments. The flow of water runs in the opposite direction to the blood this creates a counter current which causes optimum diffusion of oxygen due to the greater oxygen concentratin in the water,compared to the concentration in the blood. This means that an equilibrium wont be reached so oxygen will be constantly diffusing into the blood stream.
Gas Exchange in Insects
Insects have a chitinous exoskeleton, their bodies have a small surface area to volume ratio therefore they cant have gas diffusion through their body surface. So in an insects gas exchange system they transport oxygen directly to their cells . Air moves into the tracheae through pores on the…