6.3 Gas exchange in fish

Question 1

describe the structure of fish gills:

Answer 1

gill filaments are stacked
they have gill lamellae at right angles to the filaments (increasing SA)
they have a good blood supply

Question 2

describe how a fish exchanges gases

Answer 2

water is taken in through the mouth and forced over the gills
gases are exchanges between the water and the blood vessels in the gills

Question 3

explain the difference between parallel flow and counter-current flow

Answer 3

parallel - blood and water flow in the same direction
counter-current - blood and water flow in opposite direction

Question 4

How does counter-current allow efficient gas exchange?

Answer 4

Blood flows against the water current
Blood always meets the water with a higher concentration of O2
This maintains a constant diffusion/concentration gradient along the whole length of the gills (filaments)