PLANT PHYSIOLOGY 1
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(1) Define each of the following terms:
essential mineral nutrient
facilitated diffusion
macronutrient
diffusion potential
active transport
symport
voltage-gated channel
ABC transporters
xylem loading
electrogenic pump
2) Briefly list the three ways in which nutrients (and water) can reach the zone around the plant roots.
3) List the major functions of the macronutrients nitrogen and potassium and indicate what are the main forms in which these elements are absorbed by roots.
4) On the axes provided draw a generalised plot of plant growth as a function of the levels of nutrient present in plant tissue. Label the axes and the different regions of the plot.
5)
Ci / Co = predicted ratio of ion concentrations inside and outside the cell at equilibrium
z = charge of ion
F = Faraday constant (96 x 103 J. volt-1 M-1 )
= electropotential charge difference across the cell membrane (Volts)
R = gas constant (8.314 J. mol-1 K-1 )
T = absolute temperature (K) ( C + 273)
(a) The Nernst equation (above) for when (electrochemical gradient) = 0, can be used to predict the cellular concentration of a particular ion at equilibrium, assuming only passive diffusion of the ion across cellular membranes. Examine the table below and accompanying text. In the space provided in the table indicate which ions are passively absorbed, actively taken up or actively excluded and briefly state your reasons.
A Comparison of Measured Tissue Ion Concentrations and
Ion Concentrations
Predicted by the Nernst Equation
|
Ion
|
Solution Conc. (mM)
|
Measured Conc. (mM)
|
Predicted Ci (mM)
|
Answer to Part (a) (passive, active absorption or exclusion? and why?) |
| K- | 1.0 | 75 | 72 | ............................................................. |
| Na+ | 1.0 | 8.0 | 72 | ............................................................. |
| Ca2+ | 1.0 | 0.8 | 5,250 | ............................................................. |
| NO3- | 2.0 | 27 | 0.0276 | ............................................................. |
| Cl- | 1.0 |
5.3 |
0.0138 | ............................................................. |
| H2PO4- | 1.0 | 0.0138 | ............................................................. | |
| - | ............................................................. |
Several root segments 1 to 2 cm long (0.20 g fresh wt. total of all segments) were shaken in 50 ml of nutrient solution at 25C for 48 h. The electropotential difference between solution and root cells averaged -110 mV. Segments were rinsed, frozen, then extracted twice in boiling water to determine the concentration of each ion in the tissues (column 3 above). The predicted Ci (column 4) was calculated from the Nernst equation. (Data are from Higinbotham et al., 1967).
(b) Using the Nernst equation provided on the previous page answer the following question. If the external concentration of Mg2+ ions is 0.2 mM what would be the internal concentration of Mg2+ ions at equilibrium, assuming only passive diffusion? Show all calculations.
6) Compare the characteristics of primary and secondary active transport and discuss their interrelatedness.
7) Discuss the primary active transport of solutes into and out of cell vacuoles.
8) Describe the mechanisms by which cells control Ca++ levels in the cytosol.
9) Describe the anatomical path of mineral uptake from the rhizosphere to the root xylem and discuss the role of transmembrane transport processes.