Gas exchange in fish

Question 1

Structure of gills

Answer 1

+Made of gill filaments and stacked up in a pile
+Gill lamella are at right angles to the filaments which increase the surface area of the gills.
+Water is taken in through the mouth and passed over the gills.

Question 2

The countercurrent exchange principle

Answer 2

Flow of water and flow of blood are in opposite directions = Countercurrent flow
Important for ensuring that the possible exchange is achieved.
∴,
1–Blood that is already well loaded with O meets H2O which has its max conc of O. ∴ diffusion from water to the blood takes place.
2–Blood with little O then meets water which has most but not all its O removed. ∴ diffusion again occurs.

∴ 80% of O in water is absorbed.