What is the new water potential of a plant cell of water potential 500kPa after immerse into pure water?

Answer 1

Water potential is the potential energy of water in a system (eg a solution or a cell) compared with pure water under the same conditions. The value of the water potential depends mainly on two factors: 1) The presence of dissolved solutes. Solutes dissolved in the water reduce the energy of the water molecules, and so lower the water potential. This happens because the solute molecules attract the water molecules and reduce their movement. The component of water potential due to solutes is called the solute potential of the solution. 2) The presence of an excess pressure, above that of normal atmospheric pressure. Pressure increases the movement of the water molecules and so increases their energy, thus increasing the water potential. The component of water potential due to pressure is called the pressure potential of the solution. The total water potential of a solution is the sum of the solute potential and pressure potential water potential = solute potential + pressure potential The pressure potential can be positive or negative. An additional pressure on the solution will be positive and increase the pressure potential. If the solution is subject to a reduced pressure (a negative pressure or suction) the pressure potential will be negative and will reduce the water potential. The solute potential is always negative and so always reduces the water potential. Pure water is given a water potential of zero (similar to the way in which the freezing point of water is given a value of 0o Celsius). So anything which reduces the energy of the water molecules (such as dissolving a solute) will reduce the water potential to below zero, and so will be negative. The movement of water depends on the difference in water potential between two systems eg two adjacent cells, or a cell and the surrounding solution. This difference is called the water potential gradient. Water will always move from the higher to the lower water potential ie down the water potential gradient. In osmosis, the two solutions involved are often at atmospheric pressure. In this case it is only the difference in solute concentration which determines the direction of water movement. Water moves from the dilute solution to the concentrated solution. The concentrated solution has a higher concentration of dissolved particles, and so has a lower solute potential than the dilute solution. Since the pressure potential is zero (no excess pressure), the water potential is equal to the solute potential. Water will therefore move from the higher water potential (ie the dilute solution) to the lower water potential (ie the more concentrated solution), down the water potential gradient. It is possible for the pressure potential to counteract the solute potential. For example, if a solute (eg salt) is added to pure water, the water potential will be reduced to a negative value. If the solution is then put under extra pressure eg in a syringe, the positive pressure potential can raise the total water potential above zero ie give it a positive value. This happens especially in plant cells, where the cell wall prevents an increase in volume of the cell. So if water enters by osmosis the extra water molecules cause the pressure inside the cell to increase. This intracellular pressure in a plant cell is called the turgor pressure. For more information see: http://en.wikipedia.org/wiki/Water_potential http://www.Colorado.edu/eeb/courses/4140bowman/lectures/4140-07.html http://www.phschool.com/science/biology_place/labbench/lab1/watpot.html

Answer 2

water potential of pure water is zero (maximum). water potential of the plant cell is 500 kPa (negative value). water always moves from higher water potential to lower water potential. a plant cell in pure water means that pure water became a solution. so water moves from pure water (solvent) to plant cell (solute) till water potential of that solution becomes equillibrium. finally the water potential of the solution becomes -250kPa. ( I am not sure. hope somebody improve it)