Gas Exchange In Fish

Question 1

Which structures does gas exchange occur over in fish?

Answer 1

1. Surface of gills
   —> gill arches, gill filaments, lamellae

Question 2

Describe blood flow in gills.

Answer 2

1. Deoxygenated blood flows into each gill filament via the afferent arteriole
2. The afferent arteriole branches into small capillaries across the lamellae. Oxygen from water diffuses into the capillaries along a concentration gradient.
3. Oxygenated blood flows out of the gill filaments via the efferent arteriole.

Question 3

Describe the counter current mechanism.

Answer 3

1. Blood and water flow in opposite directions
2. Ensures blood continually meets water with a higher oxygen concentration
3. So diffusion can occur along the whole length of the lamellae
4. So increased oxygen absorbed for increased respiration causing increased energy release for muscle contraction (swimming)

Question 4

How are gills adapted for gas exchange?

Answer 4

1. Many long thin gill filaments and many thin lamallae for large SA
2. Large number of small branching capillaries across gill plates for large SA
3. Lamellae are made of a single layer of flattened epithelial cells for a short diffusion pathway
4. Capillaries are made up of a single layer of flattened endothelial cells for a shirt diffusion pathway
5. Counter current mechanism maintains a diffusion gradient for oxygen across the whole lamallae

Question 5

Explain why fish die out of water.

Answer 5

1. Gill filaments stick together causing surface area to decrease
2. Less oxygen is absorbed into the blood
3. Less oxygen for respiration
4. Less energy released for cells
5. Cells die so fish dies

Question 6

Why do fish with gill disease breath more rapidly?

Answer 6

1. Gills get infected with bacteria
2. Descrease in filaments surface area
3. So less oxygen absorbed
4. Breathing increases to increase oxygen absorption