1. Gas Exchange GillsAlveoli

2.  Need O 2 (IN)  for cellular respiration  to make ATP  Need CO 2 (OUT)  waste product from cellular respiration Why do we need a respiratory system? food O2O2 ATP CO 2

3. What’s needed for gas exchange?  need high surface area  maximize gas exchange  gases move across by diffusion  need moist membrane  maintains cell membrane structure  gases only diffuse in water

4. Gas exchange has many forms one-celledamphibiansechinodermsinsectsfishmammals

5. Gills: Countercurrent  Water carrying gas flows in one direction, blood flows in opposite direction  maintains diffusion gradient over whole length of gill capillary  maximizing O 2 transfer from water to blood

6. Tracheal System  air tubes branching throughout body  gas exchanged by diffusion across moist cells lining terminal ends, not through open circulatory system

7. Gas Exchange in Humans  Concentration gradient & pressure drives movement of gases into & out of blood at both lungs & body tissue  both oxygen and carbon dioxide diffuse from an area of high concentration to an area of lower concentration  (see fig 11.9 page 452) bloodlungs CO 2 O2O2 O2O2 bloodbody CO 2 O2O2 O2O2 capillaries in lungscapillaries in muscle

8. How Blood Transports Gases see figure 11.10 (page 453) - Both O 2 and CO 2 are transport by blood. - About 99% of O 2 is carried by hemoglobin (protein in red blood cells) - About 23% of CO 2 is carried by hemoglobin 77% is carried by blood fluid - When CO 2 reaches the lungs, it diffuses into the air in the alveoli