gas exchange in fish and countercurrent exchange in principle.

Question 1

Why do fishes need a gas exchange?

Answer 1

• Fish are waterproof and they have a small surface area to volume ratio. This is why they require a gas exchange, which is the gills.

Question 2

How do they maintain the concentration gradient?

Answer 2

Fishes obtain oxygen from the water, but there is 30 times less oxygen in water, so they have a special adaptation that helps them maintain a concentration gradient to enable diffusion to occur.

Question 3

What are the gas exchange surface features?

Answer 3

• Large surface area to volume ratio
• Short diffusion distance
• Maintained a concentration gradient

Question 4

How can the rate of diffusion be calculated?

Answer 4

Using the Ficks law

Question 5

What is the Ficks law?

Answer 5

Diffusion = surface area times difference in concentration/length of diffusion path.

Question 6

What is the fish gill anatomy?

Answer 6

There are four layers of gill on both sides of the head.
- The gills are made up of stacks of gill filaments
- Each gill filament is covered in gill lamellae, positioned at right angles to the filaments.
- This creates a large surface area.
- When fish open their mouth, water rushes in and over the gills and then out through a hole in the side of their head.

Question 7

What are the three adaptations for efficient gas exchange?

Answer 7

• Large surface-to-volume ratio
• Short diffusion distance
• Maintaining concentration gradient

Question 8

Feature of the large surface area to volume ratio.

Answer 8

Large surface area to volume ratio created by many gill filaments covered by many gill lamellae.

Question 9

Feature of the short diffusion distance.

Answer 9

Short diffusion distance due to a capillary network in every lamellae and every gill lamellae.

Question 10

Feature of the concentration gradient.

Answer 10

Maintaining concentration gradient helps countercurrent flow mechanism.

Question 11

What is the countercurrent exchange principle?

Answer 11

This is when the water flows over the gills in the opposite direction to the flow of blood in the capillaries.
Countercurrent flow ensures that equilibrium is not reached.
This ensures that a diffusion gradient is maintained across the entire length of the gill lamellae.