Salam everybody... No I must be more specific so, helo0o biologists..
[c=12]Long time ... No sea .. Thought I'd wave a HELLO your way To say I'm thinking of ya ![/c]
I hope all of you ok..
I come today.. After you forgot me ..
Any way.. I was did experiment in the lab .. It’s related to course of plant physiology ..
The experiment name was “Tissue-water relation in potato”
I will leave you now with my experiment..
Introduction:
Water potential is the tendency of water to move from one place to another. It is typically measured in units of atmospheric pressure: pascals or pounds force per square inch or bars or dynes per square centimeter. It is a measure of the ability of a solution to absorb water by osmosis.
Pure water can absorb no more water - it has a defined water potential of zero. Solutions, however, can absorb more water, because all solutions have negative water potentials. The stronger the solution, the more negative its water potential. It is possible for the water potential to be positive or negative depending on the size of Ψp or Ψπ .(1)
Aim:
Measure the water potential in plant tissue-potato tissue by tissue weight change method.
Results:
solution Initial weight Final weight
0.0 M ( H2O) 4.55 g 5.10
0.1 M 5.55 g 5.88
0.2M 5.38 g 5.41
0.3M 5.55 g 4.20
0.4M 5.06 g 4.35
0.5M 5.54 g 4.46
0.6M 5.45 g 4.25
0.7M 5.43 g 4.12
Table 1.1 : shown the change in weight of potato tube before and after soaked in different concentration of sucrose solution.
Calculation:
Calculate the change in weight.
Change in weight = final weight – initial weight
Example:
Change in H2O weight = 5.10 -4.55
= + 0.55 g
Solution (M) 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Change (g) + 0.33 + 0.03 - 1.35 - 0.71 - 1.08 - 1.2 - 1.31
Table 1.2 : The change in weight for different solution concentrations.
Percent change in weight:
Percent change in weight =[( final weight – initial weight) / initial weight] * 100
Example:
Percent change in weight for H2O = [0.55 / 4.55]*100
= 12.09 %
Solution concentration (M) 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Percent change (%) 5.61 0.55 -32.14 -16.32 -24.21 -28.23 -31.79
Table 1.3: Percent change in weight for different solution concentration
Determining the molar concentration of sucrose that gives 0% change in weight :
1*103 mol m-3 1 molal
0.2 mol m-3 x
x= 0.2 *10-4 molal
Ψs = - miRT
Ψs ( for 0.2 M sucrose ) =- 0.2*10-4 * 1*8.31 *(21.5+273)
= - 0.05 Jm-3
=- 0.05 *10-6 MPa
Determining Ψs for each solution used.(note that Ψs = Ψv)
Ψs = - m i R T
Ψs ( FOR 0.1 M) = - 1*10-4 *1* 8.31 *294.5
= -0.245JM-3
= 0.245*10-6 MPa
Solution 0.2 M 0.3M
0.4 M 0.5M 0.6M 0.7M H2O
Osmotic potential MPa *10-6 -0.05 -0.734 -0.978 -1.22 -1.47 -1.71 0
Table 1.4: The osmotic potential for the solutions used in the experiment.
Discussion:
The result above shown the different in weight of the plant tissue ( potato tube) before and after soaking. That happened because the net movement of water. therefore water move form the high concentration region to lower concentration region. If the change in the weight has a positive value this means that the potato tissue has lower water potential than does the beaker solution leading to the movement of water into the potato tissue ,so it weight increase ( like the tube with concentration 0.1 & 0.2).however, if the change in the weight has a negative value this means that the potato tissue has higher water potential than the solution in the beaker , so water moved out of the tissue into the beaker ( tube with concentration 0.3,0.4,0.5,0.6 and 0.7).
The highest percent change was shown for the potato tubes which soaked in the distilled water. This is because there was no sucrose or solutes dissolved into the distilled water ,so the free energy for the water molecules is higher than that in the potato tissue. The water potential of the distilled water is higher than the water potential of the potato tissue so , water will moved fast into the potato tissue since the water potential differences between outside and inside the potato is steep.
We all know the fact which is saying the water moves from region where water potential is high to region where water potential is lower. Since we know that when plant tissue is placed in a solution of water & sucrose, there will be net movement of water into the tissue or out of it ( not at equilibrium).
The potato tissue had in addition to high water content, solutes and mineral. When the potato tubes soaked in the pure water, the water potential of the water will be higher than that of the tissue since it has no solute molecules ( water moves into the cell because the size of the sucrose molecules large which mean they can’t pass through the plasma membrane & only water will be free to move according to it size and the presence of aquaporin on cell plasma membrane. As we increase the concentration of sucrose in the water, the water potential for it will decrease until it will become less than that of the potato tissue’ when this occur the movement of water will be from the potato tissue to the concentrated solution.) at certain concentrations there will be no net movement of water into or out of the potato cell because the water potential of the solution is the same as that of the tissue of potato. The graph 1.1 above shown the relationship between the % change in weight equal to zero at 0.2 M .At this point the amount of water get in the potato tissue will be equal to that get out which means Ψw of solution = Ψw of tissue ( increased or decreased in potato tissue will not detect at this point since equilibrium occurred) . After calculated the Ψw it was shown in table 1.4that water has the highest Ψw (Ψw for water = 0 MPa ). While tube with 0.7 M sucrose has the lowest ( -1.7*10-6 MPa). (2,3.4)
Note that because it is important when worked must covered to beaker to prevent loss of water to don’t affect the result of experiment.
References:
1. water potential,
http://en.wikipedia.org/wiki/Water_potential2. lab manual
3. What is the water potential of potato tissue?,
http://www-saps.plantsci.cam.ac.uk/records/rec234.htm 4. How is the water potential of potato cells affected the longer it is stored?
http://www-saps.plantsci.cam.ac.uk/records/rec349.htm
