In pond water In cytosol Na+ Ca2+ Mg C The graph above (which you saw in lecture
ID: 205544 • Letter: I
Question
In pond water In cytosol Na+ Ca2+ Mg C The graph above (which you saw in lecture) shows the concentration of several ions inside the cells of an aquatic plant and in the pond water surrounding it. If water potential in the plant were determined only by solute concentration, the cells would eventually explode. Obviously, they don't. Is the overall water potential (due to both solute concentration and pressure) INSIDE the cells greater than, less than, or equal to water potential outside the cells? How do each of the factors-solute concentration and pressure contribute to the water potential difference?Explanation / Answer
Water potential in plants is caused by osmosis, gravity, mechanical pressure or matrix effect including surface tention. The amount of available potential energy is reduced when solutes are added to an aqueous system because the energy in the hydrogen bonds are no longer available [ since water molecules have bound to the solute via hydrogen bonds] .
Since water potential depends on several factors and there is a tendency for it to be in equilibrium with the surroundings, the overall water potential inside the cell of aquatic plants is equal to the water potential of its surrounding medium.
Solute potential, also called osmotic potential, is higher inside an aquatic plant cell as compared to the surrounding pond water. In general, solutes reduce water potential by consuming some of the potential energy available in water. This is due to the solutes binding to the water molecule via the hydrogen bonds. Since , solute potential is one of the factors influencing water potential, an increase in solute concentration will decrease the water potential. In other words, the amount of available potential energy is reduced when solutes are added to an aquous system.
Pressure potential or turgor potential can be positive or negative. Because pressure is an expression of energy, the higher the pressure the more is the potential energy in the system. Positive pressure inside the cells is contained by the cell wall, producing turgor pressure. A plant can manipulate pressure potential via its ability to manipulate solute potential. If a plant cell increases its cytoplasmic solute concentation, the solute potential will decline and hence total potential energy will decline and the water potential between the cell and its surroundings will decline. Therefore the water will move insid the cell by osmosis.