Lesson 4 - Gas exchange in fish

Question 1

what are some challenges that fish have when extracting oxygen from the water

Answer 1

• water is denser and more viscous than air, resulting is slower diffusion of water
• water has less oxygen than air
• bony fish are very active, so have a higher oxygen demand

Question 2

meaning operculum

Answer 2

a bony protective flap that covers the gills of the bony fish, which maintain the flow of waterover the gills

Question 3

meaning gill filaments

Answer 3

occur in large stacks, and need water to keep them apart, to expose the large SA for gas exchange

Question 4

meaning gill lamellae

Answer 4

main site of gas exchange. They have a large SA and very rich blood supply

Question 5

when fish are out of the water, why can’t they survive for a long period of time

Answer 5

because the gill filaments clump together. This means a reduction in SA, which means there’s not enough efficient gas exchange taking place for the fish to survive

Question 6

what is special in the gas exchange of sharks, rays and cartilaginous fish

Answer 6

they don’t have an operculum, so they need to swim the whole time to keep water flowing in through their mouths and out through their gills.

Question 7

state 5 adaptations fish have for efficient gas exchange

Answer 7

-The lamellae provide a large surface area
-The lamellae membranes are thin to minimise diffusion distance
-The gills have a rich blood supply to maintain steep diffusion gradients
-The countercurrent flow of blood and water creates an even steeper concentration gradient
-Overlapping filament tips increases resistance, slowing water flow over the gills and allowing more time for gas exchange

Question 8

explain what the countercurrent exchange system is

Answer 8

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

Question 9

how do fish ventilate

Answer 9

fish ventilate their gills by opening and closing their mouths, changing the volume of the buccal cavity

Question 10

explain how a fish ventilates

Answer 10

1. The fish opens its mouth, increasing the volume of the buccal cavity
2. This decreases the pressure, which pulls the water into the buccal cavity
3. water flows over the gills
4. Water flows out through the operculum

Question 11

describe the structure of the gills

Answer 11

-The gills are covered by an operculum flap
-Gills consist of stacked filaments containing gill lamellae
-Gill lamellae are surrounded by extensive blood vessels

Question 12

why is parallel flow less efficient than countercurrent flow

Answer 12

because parallel flow reduces the concentration gradient, so less oxygen can be absorbed