Unit 3, gas exchange in fish

Question 1

How do fish have a large surface area to volume ratio?

Answer 1

Created by many gill filaments that are covered in many many gill lamellae

Question 2

How do fish have a short diffusion pathway?

Answer 2

Due to capillary network in every lamellae, the lamellae are also very thin

Question 3

How do fish maintain concentration gradient?

Answer 3

Countercurrent flow mechanism

Question 4

What are gas exchange surface features?

Answer 4

-large surface area to volume ratio
-short diffusion pathway
-maintain concentration gradient

Question 5

What is the feautures of the fish gill anatomy?

Answer 5

-four layers of gills on each side of the head
-gills are made up of stacks of gill filaments
-gill filaments are covered in lamellae, diffusion of gases occurs here
-when fish opens their mouths water rushes in and over the gills then out through a hole on the side of their head

Question 6

How much oxygen does water contain compared to air?

Answer 6

It has 30x oxygen less than air, so a special adaption is required to maintain concentration gradient to enable diffusion

Question 7

Why is a countercurrent better than a concurrent system? Mark scheme points

Answer 7

-to ensure equilibrium is NOT reached, so diffusion gradient is maintained over ENTIRE length of lamellae gill

Question 8

What is the countercurrent exchange principle?

Answer 8

• water flows in opposite direction to the flow of blood in capillaries
  -ensures equilibrium of oxygen in the blood and oxygen in the water is not reached
  -ensures diffusion gradient is maintained across entire length of gill lamellae

Question 9

explain two ways in which the structure of fish gills is adapted for efficient gas exchange

Answer 9

-the lamellae are thin so short diffusion pathway
-large surface area to volumes ratio so quicker gas exchange