Notes

Jambunist, the diagram below probably reminds you about the mechanism of breathing in fish.

Here's some short notes for you: 

1. Water flows over the gills in one direction. Blood flows through the cappilaries in the opposite direction. This is called the countercurrent mechanism.
2. This countercurrent mechanism is to maximize oxygen transfer.

Now, see if you can tell how the respiratory organ of the fish is adapted for gaseous exchange.