6.3 - Gas exchange in fish

Question 1

what is the adavantage of countercurrent flow as opposed to parallel flow?

Answer 1

enables more efficient gas transfer as parallel reduces the conc. gradient so less o2 is absorbed

Question 2

Countercurrent flow system

Answer 2

1. Blood and water flow over the lamellae in opposite directions
2. oxygen rich blood meets water that is at its most oxygen rich when it first moves across the gills, maximises diffusion of O2 into the blood
3. Oxygen poor blood returning from body tissues meets oxygen-reduced water that has had most of its oxygen removed - still allows diffusion of oxygen into the blood
4. maintains a steep conc gradient across the entire gill

Question 3

Adaptations of the gills for efficient gas exchange (5):

Answer 3

1. the lamellae provide a large SA
2. lamellae membranes are thin to minimise diffusion distance
3. gills have a rich blood supply to maintain steep diffusion gradients
4. the countercurrent flow of blood and water creates even steeper conc gradients
5. overlapping filament tips increase resistance, slows water flow over gills and allows more time for gas exchange

Question 4

Structure of the gills (3):

Answer 4

1. Gills have an operculum flap
2. gills consist of stacked filaments containing gill llamellae
3. gill lamellae are surrounded by extensive blood vessels

Question 5

Respiratory systems in bony fish challenges (3):

Answer 5

1. water is denser and more viscous than air, resulting in slower diffusion of oxygen
2. water has less oxygen than air
3. bony fish are very active so it has high oxygen demands