The diagram below represents the direction of flow of blood in a gill capillary. The percentage of oxygen in solution at position A, B, P, Q and R is given in the table below.

​The diagram below represents the direction of flow of blood in a gill capillary. The percentage of oxygen in solution at position A, B, P, Q and R is given in the table below.

​a) Why is the oxygen percentage low at P? (1mk)

​Blood coming from the body has supplied the tissue cells with oxygen/ oxygen has diffused out of capillary into the tissue fluid;

​b) Using evidence from the data given, suggest what will happen to oxygen in the water at  point B. (3mks)

​Oxygen concentration at B reduces/will be at lowest; because blood at P has a lower oxygen concertation creating a diffusing gradient; From A to B there is a diffusion gradient hence at B much oxygen has diffused into the from water into the blood;

​c) Name the organ into which blood coming from the capillary at Q flows. (1mk)

​Heart

​d) Suppose the flow of blood in the capillary illustrated above was in the opposite direction, explain the disadvantage it would have to the fish. (2mks)

​Amount of exchange of respiratory gasses between blood and water would reduce; because of reduced diffusion gradient;

​e) Name the principle where the blood flows in the opposite direction to another fluid. (1mk)

Counter flow system.