Transport of molecules through plants includes: transport of water transport of mineral nutrients transport of met

1. Transport of molecules through plants includes: transport of water transport of mineral nutrients transport of metabolites

2. short distance transport vs. long distance transport

3. Mechanisms of molecular movement include - diffusion - bulk flow - transport across a cell membrane via interactions with membrane proteins

4. Diffusion = net movement of molecules down anelectrochemical potential gradient(m) (has units of energy) - effects of concentration, charge, pressure

5. mj = m*j + RTlnaj + VjP + zFE m* = themof a given molecule under standard conditions RTlnaj = the chemical effect VjP = the pressure effect zjFE = the electrical effect

6. diffusion occurs down an electrochemical potential gradient in active transport, molecules can move against an electrochemical potential gradient - this is not diffusion

7. Water transport through plants - usually occurs by diffusion or bulk flow - the importance of water movement through plants is based on: 1) the importance of water in plants cells/tissues and 2) the tendency of plants to lose water to their surroundings

8. diffusion of water is influenced by - chemical effects (activity) - pressure effects * usually no electrical effect - why? electrochemical potential of water expressed using different terms the electrochemical potential (m) of water = the water potential (Y)

9. Water potential water potential (and its components) have been converted to units of pressure (megapascals) Y = Ys + YP Ys= the solute potential (osmotic potential) YP= the pressure potential (hydrostatic pressure)

10. solute potential adding solutes to water decreases the water potential Ys = -miRT **the higher the solute concentration the lower (more negative) the Ys will be

11. the pressure potential describes the effect of pressure on the diffusion of water YP= actual pressure - atmospheric pressure ** the higher the pressure, the higher the pressure potential will be

12. third component may be used to represent the effects of gravity on water movement: Y = Ys + YP + Yg Yg = the gravity potential = rgh **the greater the height, the higher the Yg

13. matric potential = Ym a combination of pressure effects and solute effects that occur when 1) water availability is very limited, and 2) the available water is in contact with charged surfaces if water is abundant, Ym is negligible (~ 0 MPa) if water is scarce, Ym decreases

14. Ym can cause Y to decrease significantly (to -2 MPa or lower) matric effects are only significant in a very dry plant or soil ** pressure component of matric effects can cause bulk flow, as well as influencing diffusion

15. different factors influence Y of water vapor (Ywv) Ywv = RT/V ln(relative humidity) or Ywv = -1.06T log (100/ % relative humidity)

16. Effects of relative humidity changes if % relative humidity is 100% , Ywv = 0 MPa if the % relative humidity decreases, Ywv decreases to < 0 MPa Effects of temperature changes if the temperature increases, Ywv decreases if the temperature decreases, Ywv increases

17. water movement through plants will occur: 1) by diffusion, down a water potential gradient or, 2) by bulk flow (along with other molecules)