Gas Exchange

1
Gas Exchange Circulation
Chapter 4
Gas Exchange in Animals
2
Why is gas exchange important?
Respiration
C6H12O6 O2 ? Energy CO2 H2O
Photosynthesis
Energy CO2 H2O ? C6H12O6 O2
3
How can an organism get O2 into its body?
Diffusion.
4
How can an organism get O2 into its body?

• For very small organisms, diffusion is fast
  enough to supply O2.
• O2 use is correlated with body mass (or volume),
  but diffusion rate depends on surface area...
• and larger organisms have lower surface
  area/volume ratios.

5
surface area/volume ratio
6
How do animals get O2?
How do animals get O2?

• Diffusion alone is enough for animals up to about
  1 mm thick...
• depending on rate of O2 use.
• Larger, faster animals need tricks to speed up
  diffusion.

7
O2 diffuses from high concentration to low
concentration.
8
Speeding up diffusion

• Gases diffuse from higher to lower concentration.
• Concentraion must be lower in organism than in
  environment.
• Will organism get enough O2? Depends on rate of
  O2 use and diffusion.
• Large, active animals have tricks to speed up
  diffusion.

9
Big aquatic animals usually have gills to provide
surface area for gas exchange.
10
Fish usually need more oxygen than invertebrates
they have more gill area than most invertebrates.
11
Faster fish have bigger gills. index of relative
gill surface area
Mackerel 2551
Toadfish 137
12
Speeding up diffusion

• Increase gill surface area have thin gill
  epithelium.
• Pump water across gills.
• Pump blood through gills.

13
Operculum in Fish 1-way flow of water across gills
14
How fish speed up diffusion ventilation

• Fish use energy to pump water across gills
  (ventilation).
• At low speed, opercular pumping is used.
• Counter current of blood flow over gills

15
Fish gill structure
16
Countercurrent exchange of O2 in gills
17
Countercurrent exchange of O2 in fish gills

• Water blood flow opposite directions.
• This maximizes the concentration gradient
  speeds up diffusion.
• Equilibrium is never reached.