fish gas exchange

describe and explain how countercurrent flow leads to efficient gas exchange across fish gills

1. maintains concentration gradient for oxygen

2. due to blood capillaries and water at lamellae flowing in opposite directions, so equilibrium never reached

3. and fish is supplied with sufficient oxygen in blood, because water is next to blood but with lower conc of oxygen along the whole length of the lamallae

what is the operculum?

bony flap which protects the gills and helps maintain flow of water over gills

structure of a fish exchange system

1. four layers of gills on both side made up of stacks of thousands of gill filaments

2. gill filaments covered in MANY gill lamellae which are positioned at a right angle

3. giving it a large surface area

4. short diffusion distance provided by these being only a few cells thick with blood capillaries, also gills covered thin epithelium.

how do fish receive oxygen?

1. water moves into mouth as pressure outside mouth is higher than inside

2. floor of mouth lowers and volume inside mouth increases

3. opercular valve shuts and water remains in the mouth

4. lower pressure in the gill lamellae, higher in mouth

5. floor of mouth rises to close and open the opercular valve

6. water moves along pressure gradient over the gills

how does the countercurrent flow maintain concentration gradient?

water flows over gills in the opposite direction of the blood in the capillaries, preventing equilibrium from ever reaching, so diffusion occurs across the entire length of lamellae