Ch2 Adaptations to the Physcial Environment - Water and Nutrients4.pdf

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University College Courses
Spencer Barrett

 as soils dry, the remaining water is held tighter b/c a greater proportion lies close to the surfaces of soil particles  most crop plants can extract water from soils with water pot. down to -1.5MPa  drought-adapted species can from even drier soils  wilting coefficient wilting pointt) is a water potential of -1.5MPa  at lower water pot., plants wilt even if some water remains Osmotic Potential and Water Uptake by Plants  solutes are dissolved substances in water which influence the diffusion of water molecules  water tends to move from regions of low solute conc. to regions of high solute conc.  osmosis is the process whereby the fluid in a cell has a high conc. of ions and other solutes (thus a low water potential), water tends to move from the envmt into the cell  osmotic potential is the force with which an aqueous soln attracts water by osmosis  this potential in roots cause water to enter the roots from the soil against the attraction of soil particles and the downward pull of gravity  the problem is that ions and other solutes diffuse through water  from areas of high solute conc. to areas of low solute conc.  so, as water is coming into the cell, solutes tend to move out  eventually, conc. would come to equilibrium in and out of the cell  but there will be no net movement of water across cell membrane  cells prevent equalization in 2 ways: 1. a cell membrane cam be semipesemipermeablee small molecules and ions can diffuse across it, but larger ones can’t)  CHO and proteins too big, remain inside cell, maintain low water pot.
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