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Unformatted text preview: B I O L O G Y 12 2 3 2-Feb-10 Gardiner 1 Gas Exchange in Plants No Trachea, no gills, no lungs How Do They Do It? 3 B I O L O G Y 12 2 3 2-Feb-10 Gardiner 2 Remember In plants all gas exchange is done locally Each living cell exchanges gas directly with environment No special system for gas exchange as in animals Vascular tissues do not transport gases to tissues B I O L O G Y 12 2 3 2-Feb-10 Gardiner 4 B I O L O G Y 12 2 3 2-Feb-10 Gardiner 5 Gas Exchange Occurs by diffusion across a cell membrane Gas must first dissolve in a film of water No serious problem for aquatic plants and protists Each in direct contact with water or only a few cells away B I O L O G Y 12 2 3 2-Feb-10 Gardiner 6 Kelp Large only in one or two dimensions Kelps 60 to 70 metres in length Blades very thin No cell very far from surface Total gas exchange area is large in relation to volume of algae B I O L O G Y 12 2 3 2-Feb-10 Gardiner 9 Land Plants In land plants the requirements of water conservation conflict with those of gas exchange 1. Respiratory surface area of adequate dimensions 1. Roots - branching, root hairs, mycorrhizae 2. Leaf intercellullar spaces B I O L O G Y 12 2 3 2-Feb-10 Gardiner 10 Land Plants 2. Protecting fragile gas-exchange surface 1. Outer body coverings 1. Waxy cuticle 2. Bark-however these make maintenance of an adequate exchange surface difficult B I O L O G Y 12 2 3 2-Feb-10 Gardiner 11 Land Plants 3. Keeping the tissues moist 1. Xylem delivers water to cells to keep them moist 2. Bark, epidermis and cuticle help retard water loss 2-Feb-10 Gardiner 12 SYSTEM LARGE SURFACE AREA SMALL DISTANCE CONCENTRATION GRADIENT Human lungs 600 mil ion alveoli with a total area of 100m each alveolus = 1 cel thick constant ventilation replaces the air Fish gil s feathery filaments with secondary lamel ae lamel ae = 2 cel s thick...
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- Fall '09