S.5 And S.6 Biology Gaseous Exchange (1) Caltec S.5

GASEOUS EXCHANGE │ FEBRUARY 2017 │ Author: DONGO SHEMA F +256 782 642 338 Page 1 of 32 TERMS USED IN GASEOUS EXCHANGE GASEOUS EXCHANGE The uptake of molecular oxygen (O 2) from the environment and the discharge of carbon dioxide (CO 2) to the environment by cells RESPIRATORY MEDIUM (gaseous exchange medium) The source of oxygen; air for la nd animals and water for aquatic animals. Amount of oxygen in water varies (~ 1.03% in fresh water and 0.85% in sea water) but is always much less than in equal volume of air, being even lower in warmer, saltier, dirtier water than in cooler, fresh, cleane r water. RESPIRATORY SURFACE (gaseous exchange surface) The b oundary between the external environment and body interior. VENTILATION The movement of air between the gas exchange medium and respiratory system to maintain appropriate concentrations of oxyg en and CO 2 in body fluids. Ventilation occurs through inspiration and expiration RESPIRATION Chemical reactions by which food is bro ken down to release energy in cells COMPARISON OF WATER AND AIR AS GASEOUS EXCHANGE MEDIA Property Air Fresh water Oxygen volume (cm3/l) 210 8 Oxygen composition (%) 21 Variable, but much less than an equivalent volume of air Diffusion rate (arbitrary units) 1 (10000) 10-5 (1) Viscosity (arbitrary units) 1 100 Density (arbitrary units) 1 1000 Stability of oxygen to temperature increase Stable Decreases Gas exchange surface needs supporting Yes No EXAMINATION TYPE QUESTION (a) Compare the suitability of air and water as gas exchange media in animals / Comment on the suitability of air and water as media for gase ous exchange in animals . (1) Air is much richer in oxygen than water, therefore much less volume of air is required to pass over the respiratory surface to satisfy the oxygen demands of …