Gas exchange - fish

Question 1

How are fish gills adapted for gas exchange?

Answer 1

They are highly branched and folded - large surface area

Thin tissue - short diffusion pathway between water and blood

Covered in lamellae - increases surface area

Counter current system - maintains a steep conc grad between water and blood

Blood circulation replaces blood saturated with oxygen

Ventilation replaces water as oxygen is removed

Question 2

What is counter-current flow?

Answer 2

Water and blood flow in opposite directions which maintains a conc grad along the whole length of the gill

so equilibrium is not reached. This is because

water is always next to blood with a lower conc of oxygen

so oxygen can always diffuse from the water to the blood.

Question 3

What’s the gas exchange surface in fish?

Answer 3

Gills

Question 4

How are lamellae adapted for efficient gas exchange?

Answer 4

They have lots of blood capillaries and a thin surface layer of cells to speed up diffusion

Question 5

How does the countercurrent mechanism allow for the maximum amount of oxygen to pass into the blood flowing through the gills.

Answer 5

A diffusion gradient is maintained across the whole length of the gill so diffusion can occur throughout the length of the gill. If water and blood flowed in the same direction equilibrium would be reached.