Water Potential

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APPROVAL SHEETThe complete report of practicum plant physiology with title Measurment of water potential in Plant tissue, created by: Name ID Class Group : Nur Fahmi Utami : 101 404 155 : Biology Bilingual :V

it has been checked and consulted to Assistant/ Assistant Coordinator shall be accepted. Makassar, Mei 2nd 2012 Assistant Coordinator, Assistant,

Risna Irawati, S.Pd

Yusmar Yusuf NIM . 081404172

Known by, Lecturer of Responsibility

Drs.Ismail, M.S NIP . 196112311986031015


A. BackgroundPlants will develop normally and thrives as well as active when the cells filled with water. At one point in time when development, water supply shortages plant, the water content in plants decreased and the rate of development is determined by the rate of all the functions is its also declining. If the situation is prolonged drought could be killed the plants. The simple and appealing explanation for osmosis is the concentration of water explanation--water in pure water is simply more concentrated than water in solutions because the solute has to take up some room in the solution. According to this idea, water diffuses into a hyper osmotic solution because it is diffusing down its concentration gradient. Apart from gradients in potential required for water entry, the water potential of the tissue may also affect growth rates directly because of the role of turgor in cell enlargement. The behavior of tissue varies considerably in this regard. At one end of the range, growth rate may be inversely proportional to the water potential of the tissue, becoming zero at the water potential which corresponds approximately to zero turgor. Osmosis process also Occurs in living cells in nature. Changes in cell shape occur if there is on a different solution. Cell located in an isotonic solution, the volume will be constant. In this case, the cell will receive the same and lose water. The last experiment, we measured the water potential of plant tissues with high levels of salt (NaCl) is different. In this lab we will use the Chardakov and Gravimetric techniques to determine the water potential (w)

of a potato tuber cells. We will determine the solute potential (s) by

the Freezing Point Depression Method. We will determine the solute potential (s) by the Freezing Point Depression Method. Pressure in the cells can be arithmetically calculated once s



are known. Pressure in the cells

can be arithmetically calculated once s and w are known.

B. The PurposeTo measure of water potential value on potato tuber tissue. C. The Benefit Students University can be more understand about how to measure the water potential value, especially in Solanum tuberosum.

CHAPTER II PREVIEW OF LITERATUREOsmosis is the diffusion of water across a semi permeable membrane from an area where more water to areas with less water. Osmosis is determined by the chemical potential of water or water potential, which describes the ability of water molecules to be able to perform diffusion. A large volume of water will have excess free energy than the little volume, under the same conditions. A free energy per unit amount of substance, especially per gram molecular weight (mol of free energy-1) is called chemical potential. Solute chemical potential approximately proportional to the concentration of the solute. The diffusing solute tends to move from areas of higher chemical potential to regions of lower chemical potential (Sasmitamihardja, 1996). The absolute value of water potential is not easily measured, but the difference can be measured. As a handle or the base potential of pure water. So the water potential is the difference in free energy or chemical potential per unit molar volume of pure water and a solution at the same temperature. Ppotential of pure water at atmospheric pressure is zero, and the water potential in the cell and the solution was less than zero or negative (Ismail, 2012). Water potential is an expression of free energy status of water, a measure of power That Causes water to move into a system, Such as plant tissue, soil or the atmosphere or from some other part that gets into one system. Water potential is probably the most useful parameter to be measured in relation to the soil system, plants and atmosphere (Ismail, 2009). Osmotic potential is the potential Caused by the solutes. The sign is always negative. Potential pressure is the pressure potential hydrostaticity caused by cells in the cell wall. Its value is marked with numbers can be positive or negative as well. Increase of pressure (pressure Turgid formation) resulted in more positive pressure potential. Potential due to the bonding matrix of water in colloidal protoplasm and surface (cell wall). Therefore, the above equation can be simplified, tissue water potential is determined by immersing the tissue sections in

a series solution of sucrose or mannitol (non-electrolyte) which can be known concentration (Ismail, 2009). The entry of water into plant tissue is essential for cell enlargement. Since water absorption occurs along graldients of decreasing water potential, the water potential of growing plant tissue must be below that of the water supply. The steepness of the gradient should depend to the resistance of the tissue to water flow. Efforts to estimate gradients in potential of growing plant tissue have taken 2 main approaches. First, the water potential of the tissue and environment have been deternmined by transferring the growing tissue to media containing solutes and letermining the potential of the solution. however, in addition to problems associated with the penetration of solutes inito the tissue, the interpretation of these experiments is made difficult by the need to use reversible chainges in size to identify tissue water potentials while the plant material is growing irreversibly. In the second approach, measurements of the resistance to water entry have been made by noting the half-time for equilibration of tissue segments in deuterated water or in soltutions of various Concentrations (Boyer, 1968) According to Anonymous (2012), as osmosis is a type of diffusion the same things that affect diffusion have an effect on osmosis some of these things are: The concentration gradient - the more the difference in molecules on one side of the membrane compared to the other, the greater the number of molecules passing through the membrane and therefore the faster the rate of diffusion. The surface area - the larger the area the quicker the rate of diffusion The size of the diffusing particles - the smaller the particle the quicker the rate and polar molecules diffuse faster than non-polar ones. The temperature - the higher the temperature the more kinetic energy the particles have and so the faster they move.


A. Date and Place Day/Date Time Place : Thursday, April 11th 2012 : At 10.50 13.00 pm : Biology Laboratory of right side in 3rd floor at FMIPA UNM

B. Tools and Materials 1. Tool a. Drill 0.6 to 0.8 cm diameter cork 1 piece b. c. d. e. f. g. 3 pieces of razor blade 8 pieces of filter paper Stopwatch 1 piece Analytic scales of 1 pc Petri dish 8 pieces Tweezers

2. Materials a. b. c. Potato tubers (Solanum tuberosum) Distilled water Sucrose solution of 0.1 M - 0.8 M

C. Work Procedure 1. Prepared 10 pieces of Petri dishes, each filled with 10 ml of solution like that: distilled water, a solution of 0.1 M sucrose, 0.2 M, 0.3 M, 0.4 M, 0.5 M, 0.6 M, 0.7 M, and 0.8 M. 2. Performed the following steps quickly, making 10 in potato cylinders with a diameter of 0.8 cm, each with a length of 4 cm, remove the skin. Should all cylinders in potato tubers from the tuber only. Put the cylinder in a closed container. 3. Used a razor blade, cut a potato cylinder into thin slices with a thickness of 1-2 mm.


Rinsed the thin slices of potato with distilled water quickly, dry with filter paper and weighed. Subsequently enter into a sucrose solution that had been prepared. Do this on each cylinder of each potato to the next solution.


Cylinder soak for 1 hour, remove the slices from each Petri dish, then dry with a paper suction and weighed. Do this for all instances of the experiment


The following formula to calculate the weight change, use the following formula:


Then made a chart and Plot percent weight change on the ordinate and the concentration of sucrose solution (in molar) on the abscissa.


Tissue water potential can be obtained after first calculating osmotic potential for each concentration of sucrose solution. Used the following formula: -s = MIRT Where M = molarities of sucrose solution I = ionization constant, for sucrose = 1 R = gas constant () 0.0831 bar / degree mol T = absolute temperature = (C + 273) The formula above is used to calculate the osmotic potential of sucrose solution temperature.


Then determined with polarize of the graph, the concentration of sucrose which does not produce weight change. And calculate s of this solution. s value is proportional to water potential (w) tissue.


A. Observation Result Consentration of Sucrosa solution (M) 1,4 1,6 1,8 2 2.2 2,4 2.6 2,8Data analysis

The first weight (gr) 4,50 4,40 4,35 4,30 4,45 4,40 4,00 4,35

The final weight (gr) 4,50 5,50 4,50 5,00 3,50 3,50 4,50 4,00

The change Percentation of weight of weight (gr) (%) 0 1,10 0,25 1,30 -0,95 -0,90 0,50 -0,35 0 25 0.57 30,2 21,3 20,4 12,5 0,80

Weight change = final weight - initial weight

1. Sucrose solution with concentration of 1,4The first weight The final weight Weight change = 4,50 grams = 4,50 grams = 0 grams

Percent weight change = 0