Exchanging gases

1. Exchanging gases Key understanding: To discuss features of effective surfaces of gaseous exchange and the mechanisms for gas exchange in animals

2. Cellular Respiration • What do we know? • What are the inputs? • What are the outputs? C6H12O6 + 6O2 6CO2 + 6H2O + (36-38ATP)

3. Carbon dioxide forms acid in solution so it must be removed • Oxygen needed in cellular respiration • Some animals and plants can exchange gases direct from cell→environment • Others need a system

4. Mechanism for gas exchange in mammals Respiartion • http://www.youtube.com/watch?v=HiT621PrrO0

5. Gas exchange • Always takes place by diffusion across a moist plasma membrane (extracellular fluid) • Oxygen and carbon dioxide are uncharged (non-polar) molecules so diffuse across membranes • The rate of diffusion depends on: size and maintenance of concentration gradient, and properties of the membrane

6. Fick’s formula Amount transferred = Permeability x surface area x concentration gradient Distance of diffusion The following illnesses can effect gas exchange because they affect one of the factors listed in formula • Emphysema reduces the surface area of lungs • Pneumonia increases distance of diffusion • Anaemia reduces concentration gradient

7. Features of an efficient gas exchange surface: • Large surface area • Thin barrier and made of material that allows gas to pass through it easily • Adequate supply of gas being transferred • Efficient removal of substance after transfer

8. Gills • Water flows in one direction: through the mouth and pharynx, past the gills and out under the operculum • Countercurrent flow: blood flows in opposite directionto the water so blood can extract up to 90% of the oxygen in the water (mammals can only extract 25%!)

9. Lungs • Air breathed in and passes into pharynx. • From here it passes into the airways- the trachea, paired bronchi and branching bronchioles. • Terminal air sacs called alveoli. • This is the site of gas exchange .

11. Features for efficient gas exchange • Trachea and bronchi lined with ciliated cells which produce mucus - traps dust and bacteria and transports them back to the pharynx, where they are swallowed • Alveoli provide large surface area for gas exchange • Alveoli richly supplied with blood capillaries • Diffusion barrier very thin

13. Respiratory pigments • Increase the efficiency of gas transport in animals. • Consist of proteins complexed with iron and copper • Haemoglobin is the most widely distributed pigment found in all vertebrates and many invertebrates. • Oxygen-carrying molecules • Increasing the oxygen-carrying capacity of blood reduces amount of energy needed to pump blood

14. Haemoglobin • Mammalian respiratory pigment • Increases oxygen-carrying capacity 100 fold • In red blood cells • Contains iron • 4 oxygen molecules can combine with 1 haemoglobin molecule

15. In lungs high O2 Hb + 4O2 → Hb(O2)4 Hb + 4O2 ← Hb(O2)4 In tissue low O2 • When haemoglobin combines with oxygen it is called Oxyhaemoglobin • Muscles contain type of haemoglobin called Myoglobin. These carry a reserve store of oxygen.

16. What about the carbon dioxide? • 7% dissolved in blood plasma • 23% combines with haemoglobin molecules forming carbaminohaemoglobin • 70% converted to hydrogen carbonate ions in red blood cells and transported to plasma

17. Resources • Chapter 8 of Heinemann text • Complete p145 -147 of Biozone. Use the answer book for the questions. • p148 Biozone – Respiratory pigments