Features of effective gas exchange surfaces include:
- Large surface area
- Thin wall (short diffusion distance)
- Good blood supply
The larger the organism, the more difficult it is to exchange materials.
Gas Exchange in Fish
Fish can't get oxygen directly from the water because of their scales.
Their gills are made of many layers of tissue, which allows for:
- rich blood supply
- thin layers - short diffusion distance
- moist (in water)
Water being pumped over the gills maintains the concentration gradient.
If the fish is not in water, the gills stick together, so no gas exchange can take place.
Gas Exchange in Insects
Insects have an internal respiratory system.
The spiracles open when there is a need for oxygen, and they close when there is no need. (This prevents water loss.) The spiracles lead into tubes which lead to the cells.
Most gas exchange takes place in the trachedes:
- tiny tubes
- air pumped in/out - maintains concentration gradient
However, there is no blood supply.
Gas Exchange in Amphibians
Tadpoles have external gills, which have
- a large surface area and
- a rich blood supply
They get all their oxygen by diffusion from the water through the gills.
In frogs gas exchange happens through the skin and mouth.
They have simple lungs for when they are on land, which make a large surface area for gas exchange.