Gas Exchange & Circulation

Chapter 4

Gas Exchange in Animals

Why is gas exchange important?

C6H12O6 + O2 Energy + CO2 + H2O

Energy + CO2 + H2O C6H12O6 + O2

Photosynthesis:

Respiration:

How can an organism get O2 into its body?

Diffusion.

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.

surface area/volume ratio

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.

O2 diffuses from high concentration to low

concentration.

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.

Big aquatic animals usually have gills to provide surface area for gas

exchange.

Fish usually need more

oxygen than invertebrates;

they have more gill area than

most invertebrates.

Faster fish have bigger gills.

index of relative gill surface area

QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.

Mackerel: 2551

Toadfish: 137

Speeding up diffusion

1. Increase gill surface area; have thin gill epithelium.

2.Pump water across gills.

3.Pump blood through gills.

Operculum in Fish1-way flow of water across gills

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

Fish gill structure

Countercurrent exchange of O2 in

gills

Water & blood flow opposite directions.

This maximizes the concentration gradient & speeds up diffusion.

Equilibrium is never reached.

Countercurrent exchange of O2 in fish gills