Gas Exchange In Fish

Question 1

What does partial pressure of oxygen mean

Answer 1

• Partial pressure is a measure of the concentration of a gas

High partial pressure of oxygen = higher conc of oxygen

Lower partial pressure of oxygen = lower conc of oxygen

Question 2

Does water have a lower or higher ppO2 compared to air?

Answer 2

Lower
It is also a lot denser than air

Question 3

Do fish have a small or large SA:vol?

Answer 3

Small SA:Vol ratio as they are multicellular

Question 4

Why do fish have gills?

Answer 4

Fish cannot take in air through their outer surface and instead have specialised internal structures called gills for efficient gas exchange with water

Question 5

How are gills specialised for gas exchange?

Answer 5

1. Many gill filaments on which are many lamellae - increase surface area
2. Lamellae have many blood capillaries and have a thin surface - reduces diffusion pathway

Question 6

What is counter current exchange and why is it needed?

Answer 6

Water moves in opposite direction to the flow of blood, ensures that water higher in oxygen will flow next to blood with a lower concentration of oxygen so that a concentration gradient is maintained along the hole length of the lamella and this will maximise the amount of diffusion.

Basic principle is taht the ppO2 will always be slightly higher in the water than in capillary so oxygen will always diffuse down conc gradient into capillary

Question 7

What percentage of oxygen is absorbed into the blood with counter current flow?

Answer 7

80%

Question 8

What percentage of oxygen is absorbed into blood with parallel flow?

Answer 8

50% - since gradient between blood and water only exits over 50% of the lamella