Exchange and transport

Gas exchange
1. Principles
  1. Large SA: volume ratio
  2. Thin, permeable exchange surface
  3. Conflicts with need for water conservation
2. Fish
  1. Structure of gills
    1. Gill filaments and lamellae
      1. Maximised surface area
  2. Countercurrent flow
    1. Concentration gradient of oxygen along entire gill lamella
    2. Maximal diffusion of oxygen into blood
3. Plants
  1. Stomata on lower surface of leaf
    1. Oxygen out, carbon dioxide in
      1. Photosynthesis
  2. Spongy mesophyll cells have air spaces
    1. Greater SA: volume ratio
4. Insects
  1. Waterproof exoskeleton prevents water loss
    1. Spiracles allow diffusion of gases in and out
      1. Open and close to ventilate tracheae
  2. Tracheae - tubes for movement of oxygen through insect
    1. All body cells within short diffusion pathway of tracheae
    2. Thin walls - short diffusion pathway
  3. No mass transport system - limits insect size
Circulatory system
1. Structure of blood vessels
  1. Elastic layer
    1. Stretches during systole
      1. does NOT "expand/contract"
    2. Recoils during diastole
    3. Smooths out blood flow
  2. Muscle layer
    1. Contracts/expands
      1. Controls volume of lumen
    2. Thickest in arterioles - constrict blood flow into capillaries
  3. Valves
    1. Mainly in veins
      1. Lower blood pressure
    2. Prevent back flow
2. Tissue fluid
  1. Exchanges materials between blood and cells
  2. Hydrostatic pressure forces it out of capillaries
    1. Diffusion into and out of tissues occurs
  3. Returned to circulatory system
    1. Reabsorption into capillaries
      1. Plasma proteins lower blood water potential
      2. Hydrostatic pressure and osmosis
    2. Drainage into lymph
3. Hepatic artery/vein: to and from the liver
4. Renal artery/vein: to and from kidneys
Water movement through plants
1. Through roots
  1. Water enters root hair cells by osmosis
  2. Active transport of minerals into cortex
    1. Water enters cortex by osmosis
  3. Water moves through cortex
    1. Symplast
      1. Osmosis
      2. Water moves through cytoplasm/vacuoles
      3. Passes between cells via plasmodesmata
    2. Apoplast
      1. Cohesion between water molecules
      2. Water moves through cell walls
        No membranes to cross
      3. Stops at endodermis
        Waterproof Casparian strips
2. Up stems
  1. Active transport of salts from roots to xylem
    1. Water enters by osmosis
      1. Root pressure forces water up stem
  2. Cohesion between water molecules
    1. Continuous stream of water
    2. Water under tension/negative pressure
      1. Diameter of xylem decreases
3. Transpiration
  1. Xerophytes
    1. Thin leaves
    2. Few stomata
    3. Thicker waxy cuticles/epidermal layers
  2. Water evaporates from mesophyll cells
    1. Diffuses out via stomata
    2. Water enters leaves from xylem by osmosis
  3. Factors
    1. Temperature (+)
    2. Light (+)
    3. Humidity (-)
    4. Wind (+)

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Exchange and transport

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	Created by Stephen Cole almost 11 years ago