Potato and Osmosis Investigation
Some background Information: Water Potential and Living Plant Cells
Plant Cells in Pure Water: If plant cells are placed in pure water (a
hypotonic solution) water will initially move into the cells. After a
period of time the cells will become turgid. Turgor pressure is the
pressure exerted against the cell wall by contents of the cell. At
first most water movement is into the cell. As the turgor pressure
increases water will begin to diffuse out of the cell at a greater
rate, eventually equilibrium will be reached and water will enter and
leave the cell at the same rate.
Free Energy and Water Potential: Free energy can be simply defined as
the energy available (without temperature change) to do work. Chemical
potential of a substance is the free energy per mole of that
substance. Water potential is the chemical potential of water and is a
measure of the energy available for reaction or movement (Bidwell
1974:59). Water potential is important when studying osmosis because
it measures the ability of water to move, water always moves from
areas of high potential to areas of low water potential.
The formula for calculating water potential is:
Water Potential = Osmotic Potential + Pressure Potential
Water Potential in Plant Cells: Water will move by osmosis into and
out of cells due to differences in water potential between the cell
and its surroundings. Remember that water always moves from areas of
high potential to areas of low water potential.
Some Basic Principles:
Â· Water always moves from high water potential to low water potential.
Â· Water potential is a measure of the tendency of water to move from
high free energy to lower free energy.
Â· Distilled water in an open beaker has a water potential of 0(zero).
Â· The addition of solute decreases water potential.
Â· The addition of pressure increases water potential.
Â· In cells, water moves by osmosis to areas where water potential is
Â· A hypertonic solution has lower water potential.
Â· A hypotonic solution has higher water potential.
References: Bidwell, R.G.S. 1974. Plant Physiology. MacMillan Publ.
Co. New York.643pp.
Weier, T. E., C.R. Stocking and M.G. Barbour.1974. Botany: An
Introduction to Plant Biology. 5th ed. John Wiley & Sons. New York.
What is Sucrose and what is it made up of?
Sucrose is made up of three elements which can be found in the
periodic table, they are: Oxygen, Hydrogen and Carbon. But how many
components are found with each element?
Oxygen contains: 11, 16 x 11 = 176g
Hydrogen has: 22, 1 x 22 = 22g
Carbon holds 12, 12 x 12 = 144g
= 342g in 100dmÂ³
That means there is 342g of sucrose in 1000cmÂ³ of distilled water in a
1 molar solution, however we must divide...