6.3 Gas exchange in fish

Question 1

Why isn’t a fishes body adequate to supply and remove respiratory gases

Answer 1

There outer layer is waterproof so gas tight
They are also quite large so have a small surface area to volume ratio

Question 2

What are gill filaments
What are gill lamellae and what is their function

Answer 2

Gill filaments make up the gills, and stack up like pages in a book.

Gill lamellae are at right angles to the filaments and they increase the surface area of the gills

Question 2

What is the internal gas exchange surface called in fish

Where are they located

Answer 2

Gills

Located behind the head of the fish

Question 2

What is countercurrent flow and why does it occur

Answer 2

The flow of water over the gill lamellae and the flow of blood within them are in opposite directions

It maintains a steep diffusion gradient for oxygen

This is to get the maximum amount of gas exchange occurring as if they flowed in the same direction less gas exchange would take place

Question 2

How does water pass through the gills

Answer 2

Water is taken in through the mouth of a fish and forced over the gills and out through an opening on each side of the body

Question 3

How does countercurrent flow occur

Answer 3

. Blood and water that flow over the gill lamellae do so in opposite directions

. Blood that is well loaded with oxygen meets the water which has its maximum concentration of oxygen .
Therefore diffusion of oxygen from the water to the blood can occur.

. Blood with little oxygen in it meets water which has had most, but not all of its oxygen removed.
Again, diffusion of oxygen from water to blood occurs

Question 4

How does countercurrent flow improve oxygen uptake …
Examples

Answer 4

With countercurrent flow, oxygen uptake is maintained across the entire width of the gill lamellae.
This means about 80% of the oxygen available in the water is absorbed into the blood

If they had been flowing in the same direction then the diffusion gradient would only be maintained across part of the length of gill lamellae and only 50% of available oxygen would be absorbed into the blood

Question 5

How are the gills adapted for a large surface area

And a short diffusion distance

Answer 5

There are many gill filaments covered in gill lamallae which lie at right angles to the filaments, creating a large surface area

There is a capillary network in every gill lamellae and the lamellae are very thin