Exchange and transport

Exchange and transport

1. Gas exchange

   • Principles
     • Large SA: volume ratio
     • Thin, permeable exchange surface
     • Conflicts with need for water conservation
   • Fish
     • Structure of gills
       • Gill filaments and lamellae
         • Maximised surface area
     • Countercurrent flow
       • Concentration gradient of oxygen along entire gill lamella
       • Maximal diffusion of oxygen into blood
   • Plants
     • Stomata on lower surface of leaf
       • Oxygen out, carbon dioxide in
         • Photosynthesis
     • Spongy mesophyll cells have air spaces
       • Greater SA: volume ratio
   • Insects
     • Waterproof exoskeleton prevents water loss
       • Spiracles allow diffusion of gases in and out
         • Open and close to ventilate tracheae
     • Tracheae - tubes for movement of oxygen through insect
       • All body cells within short diffusion pathway of tracheae
       • Thin walls - short diffusion pathway
     • No mass transport system - limits insect size

2. Circulatory system

   • Structure of blood vessels
     • Elastic layer
       • Stretches during systole
         • does NOT "expand/contract"
       • Recoils during diastole
       • Smooths out blood flow
     • Muscle layer
       • Contracts/expands
         • Controls volume of lumen
       • Thickest in arterioles - constrict blood flow into capillaries
     • Valves
       • Mainly in veins
         • Lower blood pressure
       • Prevent back flow
   • Tissue fluid
     • Exchanges materials between blood and cells
     • Hydrostatic pressure forces it out of capillaries
       • Diffusion into and out of tissues occurs
     • Returned to circulatory system
       • Reabsorption into capillaries
         • Plasma proteins lower blood water potential
         • Hydrostatic pressure and osmosis
       • Drainage into lymph
   • Hepatic artery/vein: to and from the liver
   • Renal artery/vein: to and from kidneys

3. Water movement through plants

   • Through roots
     • Water enters root hair cells by osmosis
     • Active transport of minerals into cortex
       • Water enters cortex by osmosis
     • Water moves through cortex
       • Symplast
         • Osmosis
         • Water moves through cytoplasm/vacuoles
         • Passes between cells via plasmodesmata
       • Apoplast
         • Cohesion between water molecules
         • Water moves through cell walls
           • No membranes to cross
         • Stops at endodermis
           • Waterproof Casparian strips
   • Up stems
     • Active transport of salts from roots to xylem
       • Water enters by osmosis
         • Root pressure forces water up stem
     • Cohesion between water molecules
       • Continuous stream of water
       • Water under tension/negative pressure
         • Diameter of xylem decreases
   • Transpiration
     • Xerophytes
       • Thin leaves
       • Few stomata
       • Thicker waxy cuticles/epidermal layers
     • Water evaporates from mesophyll cells
       • Diffuses out via stomata
       • Water enters leaves from xylem by osmosis
     • Factors
       • Temperature (+)
       • Light (+)
       • Humidity (-)
       • Wind (+)