Sabtu, 04 Juni 2011

Water Potential


This complete report of plant physiology which was entitled “Water Potential” was written by:

Name : Andi Citra Pratiwi

Reg. No. : 091404170

Group : IV

If this report is checked by the assistant and the coordinator of assistant, so this report is accepted.

Makassar, May ... 2011

Coordinator of Assistant Assistant

Muh. Nur Qadri Yusmar Yusuf



  1. Background

Water plays a crucial role in the life of the plant. For every gram of organic matter made by plant, approximately 500 g of water is absorbed by the roots, transported through the plant body and lost to the atmosphere. The plants will develop normally and grow actively if their cells are full of water. When the sum of water is less than the total water which is need by plant to grow, the growing rate which depends on the rates of all physiological function will also be decreased. If this condition occurs continuously, it can cause the death of plant. Even slight imbalances in this flow of water can cause water deficits and severe malfunctioning of many cellular processes. Besides that, water in plants also important to determine the movement of nutrients from the environment into the cells of plant, from cell to cell within the plant, and also from the cells of plant into the environment.

To help us understand about the movement of water, it is important to understand about the water potential. The water potential of solution within the plant system will determine the movement of water from one place to another place. Water will move from the solution which has higher water potential into the solution which has lower water potential. Water potential can be determined by summing the osmotic potential and water potential. To understand amore about the determination of water potential of plant cells, it will be a wise decision to do this experiment which was entitled “Water Potential of plant Tissue.”

  1. Purpose

This experiment is done to determine the water potential of potatoes tissue.

  1. Benefit

This experiment will be able to help the student understand about the way to determine the water potential of plant’s cells



The concept of water potential has two principal uses: first, water potential governs transport across cell membranes. Second, water potential is often used as a measure of the water status of a plant. Because of transpirational water loss to the atmosphere, plants are seldom fully hydrated. They suffer from water deficits that lead to inhibition of plant growth and photosynthesis, as well as to other detrimental effects. The process that is most affected by water deficit is cell growth. More severe water stress leads to inhibition of wall and protein synthesis, accumulation of solutes, closing of stomata, and inhibition of photosynthesis. Water potential is one measure of how hydrated a plant is and thus provides a relative index of the water stress the plant is experiencing (Zeiger. 2006).

Solute concentration and hydrostatic pressure are the two major factors that affect water potential, although when large vertical distances are involved, gravity is also important. These components of the water potential may be summed as follows: ψw = ψp + ψs + ψg. Plant cells come into water potential equilibrium with their local environment by absorbing or loosing water. The rate of water transport across a membrane and the hydraulic conductivity of the membrane (Zeiger. 2006).

Osmosis process is driven by a water potential gradient. Membranes of plant cells are selectively permeable, that is, they allow the movement of water and other small uncharged substances across them more readily than the movement of larger solutes and uncharged substances. Like molecular diffusion and pressure driven bulk flow, osmosis occurs spontaneously in response to a driving force. In simple diffusion, substances move down a concentration gradient. nIn pressure-driven bulk flow, substances move down a pressure gradient. In osmosis, both types of gradients influence transport. The direction and rate of water flow across a membrane are determined not solely by the concentration gradient of water or by the pressure gradient, but by the sum of these two driving forces, (Zeiger. 2006)



  1. Time and Place

Day/ date : Wednesday, May 4th 2011

Time : 08.00 until 09.40 am

Place : At the 2nd floor of Biology Laboratory, Mathematic and Science faculty, Makassar state university.

  1. Tool and Material

  1. Tools

  1. Balance

  2. Knife

  3. Petri dish

  4. Bor with diameter 0,6-0,8 cm

  1. Materials

  1. Solanum tuberosum

  2. Sucrose solution ( 0,1 M, 0,2 M, 0,3M, 0,4M, 0,5M, 0,6M, 0,7M, 0,8M, 0,9M)

  3. Aquadest

  1. Work Procedure

        1. Prepared 10 petri dish. Each petri dish is filled with sucrose solution fom 0,1M, 0,2M, 0,3M, 0,4M, 0,5M, 0,6M, 0,7M, 0,8M, 0,9M, and the last petri dish is filled with aquadest.

        2. Made the cylindrical potatoes which have 0,6 until 0,8 diameter, and each of them has 4 cm length. After that, put all the potatoes in a closed place.

        3. By using knife, cut the cylindrical potatoes into several thin slices, which has 1-2 mm in thickness.

        4. Wash those cylindrical potatoes by using aquadest, dried by using paper, and thendetermine the weight. After that, put it in the sucrose solution which have been prepared. Did the same way for each cylindrical potatoes for the next sucrose solutions.

        5. After 30 minutes, toothe potatoes out from the petri dish, dried by using paper, and determine the final weight. Did the same way for each potatoes in each petri dish.

        6. To determine the alterqation of weight, used the formulation below:

% weight alteration = final weight – first weight x 100%

First weight

        1. After that, made the graft and percentage of weight alteration

        2. Water potential of tissue can be found after determining the osmotic potential for each sucrose solution. Used the following formulation: -Ψs = M i R T

        3. Determine the concentration of sucrose solution which is not cause weigh alteration. And then, determine the water potential of this solution, because it has the same water potential with the water potential of potatoes tissue.



  1. Observation Result



First Weight

Final Weight




Sucrose 0,1 M

0,7 g

0,6 g

0,1 g

14,28 %


Sucrose 0,2 M

0,6 g

0,4 g

0,2 g

33,33 %


Sucrose 0,3 M

0,6 g

0,4 g

0,2 g

33,33 %


Sucrose 0,4 M

0,9 g

0,7 g

0,2 g

22,22 %


Sucrose 0,5 M

0,7 g

0,5 g

0,2 g

28,57 %


Sucrose 0,6 M

0,7 g

0,5 g

0,2 g

28,57 %


Sucrose 0,7 M

0,8 g

0,5 g

0,3 g

37,50 %


Sucrose 0,8 M

0,6 g

0,6 g


0 %


Sucrose 0,9 M

0,6 g

0,4 g

0,2 g

33,33 %



0,7 g

0,6 g

0,1 g

14,28 %

  1. Data Analysis

  • Osmotic potential of each sucrose solution

Formulation : ψs = - m i R T

ψs = Osmotic potential

m = Molality (mol/1000 g)

i = ionization constancy (1 for sucrose, as non electrolyte)

R = gas constancy (0,0821 ltr MPa/mol)

T = Temperature (0K), for room temperature = 298 0K

        1. Sucrose solution 0,1 M, ψs = - 0,1 . 1 . 0,0821 . 298 = - 2.45 MPa

        2. Sucrose solution 0,2 M, ψs = - 0,2 . 1 . 0,0821 . 298 = - 4.89 MPa

        3. Sucrose solution 0,3 M, ψs = - 0,3 . 1 . 0,0821 . 298 = - 7.34 MPa

        4. Sucrose solution 0,4 M, ψs = - 0,4 . 1 . 0,0821 . 298 = - 9.79 MPa

        5. Sucrose solution 0,5 M , ψs = - 0,5 . 1 . 0,0821 . 298 = - 12.23 MPa

        6. Sucrose solution 0,6 M, ψs = - 0,6 . 1 . 0,0821 . 298 = - 14.68 MPa

        7. Sucrose solution 0,7M, ψs = - 0,7 . 1 . 0,0821 . 298 = - 17.12 MPa

        8. Sucrose solution 0,8 M, ψs = - 0,8 . 1 . 0,0821 . 298 = - 19.57 MPa

        9. Sucrose solution 0,9 M, ψs = - 0,9 . 1 . 0,0821 . 298 = - 22.02 MPa

  1. Discussion

Potatoes which were put in sucrose solutions for several minutes undergo weight alteration. The weight alteration can occur because the osmosis process. Osmosis is the diffusion of solvent (H2O) from higher concentration of water (hypotonic solution) to lower concentration of water (hypertonic solution). Thus, the potatoes which are put in hypertonic solution will undergo weight decreasing, because the water in its tissue will flow into the hypertonic solution which has lower concentration of water. Meanwhile, the potatoes which are put in hypotonic solution will undergo weight increasing, because the higher concentration in solution will go into the potatoes tissue.

Based on the result of observation, potatoes in sucrose solution 0,1M, 0,2M, 0,3m, 0,4M, 0,5M, 0,6M, and 0,7M, undergo weight decreasing. It can occur because the water potential of solution is lower than the water potential of potatoes tissue. Since the water moves from higher water potential to lower water potential, the water in potatoes tissue will flow out to the sucrose solution. Meanwhile, the potatoes in sucrose solution 0,8M have constant weight. It means that the water potential of potatoes tissue is equal to the water potential of sucrose solution. In the other words, the sucrose solution is isotonic with the solution in potatoes tissues. Potatoes in sucrose solution 0,9 M and aquadest are also undergo weight decreasing, which means that the water potential of sucrose solution is lower than the water potential of potatoes tissue.

The data which are found from the result of observation did not show the relation of one data with another data. If sucrose solution 0,8 M is isotonic with potatoes tissues, it means that sucrose solution 0,1 M until 0,7 M should be hypotonic to potatoes tissues, and sucrose 0,9 M should be hypertonic to sucrose tissues. At the fact, none of sucrose solution which show hypotonic condition to potatoes tissues, because none of the potatoes which undergo weight increasing. Even the aquadest which should be hypertonic to potatoes solution, can not cause the weight increasing of potatoes. It may be caused by the un-accurate data taking by the apprentices when doing the experiment, and also because the apprentices did not use one potato, but they use several potatoes to make potatoes cylindrical. Since the water potential of a potato can be different with another potato, it causes the un-related data at the result of experiment.



  1. Conclusion

        1. Potatoes which are put in hypotonic solutions will undergo weight increasing.

        2. Potatoes which are put in isotonic solution will not undergo weight alteration.

        3. Potatoes which are put in hypertonic solution will undergo weight decreasing.

  1. Suggestion

Before doing this experiment, it will be better for the apprentice to take a note about some suggestions below:

        1. Learn more about water potential theory before doing this experiment.

        2. Learn about the experiment procedure before doing such an experiment.

        3. Use one potato to make several potato cylindrical to get better data.


Zeiger, E. and Taiz, Lincoln. 2006. Plant Physiology. Sinaeur Associates, Inc.

Tidak ada komentar:

Posting Komentar