Question

What mechanism results in continual diffusion of oxygen across gills because of the concentration gradient between water and blood?

	isotonic equilibrium
	countercurrent exchange
	osmotic pressurization
	ram ventilation

Answer 1

Answer:-

The correct option is (b) i.e countercurrent exchange. The reason being is that it increases the regulation of oxygen uptake along with loss of waste gases by permitting continuous diffusion of oxygen into the blood across the gills due to the concentration gradient between water and blood as exchange of gases across gill surface is very efficient.The deoxygenated water will pass out from the gill cover in order to maintain adequate levels of oxygen into the body whereas, Ram ventilation is basically a mechanism in which flow of water is maintained by opened mouth while swimming. Also when fishes are placed in isotonic equilibrium, the cells will take excess amount of water and same amount of water will leave from its body in order to maintain the equilibrium and fishes will ultimately die. Osmotic pressure is the force which is required to prevent the movement of water across the semipermeable membrane. It doesn't results in continual diffusion of oxygen across gills.

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