1. Requirements for Gas Exchange moist membrane surface area respiratory medium Air Water

2. Gills

3. Ventilation, which increases the flow of the respiratory medium over the respiratory surface, ensures that there is a strong diffusion gradient between the gill surface and the environment. Crayfish and lobsters have paddlelike appendages that drive a current of water over their gills. Fish gills are ventilated by a current of water that enters the mouth, passes through slits in the pharynx, flows over the gills, and exits the body.

4. Ventilation - gill cover

6. Terrestrial organisms Gills unsuited for an animal living on land. Air- respiratory medium Advantages of air over water higher concentration of oxygen. O 2 and CO 2 diffuse much faster in air less energy is needed to ventilate Disadvantages of air as a respiratory medium loss of water Terrestrial respiratory surfaces within the body opening to the atmosphere through narrow tubes.

7. Insects - tracheal system Trachea Gas exchange at cell by diffusion across the moist epithelium

8. Lungs Amphibians lungs & skin Reptiles, Birds & Mammals - only lungs

9. Ventilation - (breathing) Inhalation Exhalation Amphibians - Positive pressure

10. Lung Volumes - Residual Volume differences