ch7 - gas exchange and ventilation in fish

give a reasons why bony fish require specialised respiratory systems

water has lower dissolved oxygen conc compared to the atmosphere so require a steep concentration gradient of oxygen

what do bony fish have which enables them to take up oxygen from water

gills

name the structures that the gills consist of

operculum

gill filaments

gill lamellae

what do these structures do

operculum - flap which covers the gills

gill filaments - each gill consist of many stacked filaments, each filament contains loads of lamellae

gill lamellae - contain network of capillaries

how many gills does a bony fish have

4 layers of gills on each side of their head

where is the specific site of gas exchange

gill lamellae

what is the counter current flow system

water flows over the gills in the OPPOSITE direction that blood flows through the capillaries

describe how the counter current flow system works

blood with low oxygen conc passes through the capillaries in gill lamellae > oxygen from water diffuses into blood > blood rich in oxygen passes out of lamellae and out of gills

why is the counter current flow system so useful

it maintains a steep concentration gradient for oxygen since there is higher concentration of oxygen in water than blood maximising the rate of diffusion

why would parallel flow system not be as useful

equilibrium of oxygen would occur meaning there would be NO net diffusion of oxygen between the water and blood

name 3 adaptations of the gills for efficient gas exchange

large surface area = gills consist of many stacked filaments, each filament contains loads of lamellae

thin layers = gill lamellae are very thin containing network of capillaries

counter current flow system = maintains steep concentration gradient

how is a constant flow of water over the fish gills maintained

from ventilation - due to the pressure differences created by the fish opening and closing its mouth

why is ventilation important

provides oxygenated water and removes carbon dioxide

describe the mechanism of ventilation in fish

1. fish opens mouth lowering the floor of buccal cavity

2. inside buccal cavity: volume increases, pressure decreases - causing water to flow in (due to the pressure being lower inside compared to outside of the mouth)

3. fish closes mouth raising floor of buccal cavity

4. pressure in buccal cavity increases so water flows into gill cavity

5. pressure in gill cavity increases causing operculum to open so water can exit

6. when fish reopens mouth operculum shuts and cycle restarts