1. Fill in the values of the missing components of water potential for each of t
ID: 162680 • Letter: 1
Question
1. Fill in the values of the missing components of water potential for each of the 5 cells in the table below. For this problem you can ignore the gravitational and matric components of water potential. All values are in megapascals, MPa.
2. a) Which cell in problem #1 is likely in the xylem? Explain (5)
b) Which cell in problem #1 is a living cell that has lost turgor? (5)
c) Assuming a temperature of 250C, what is the solute concentration of cell B of problem #1? Show any calculations and formulae. (10)
Cell 4.0 5.0 2.5 UPP 0.5 1.0 1.0 Ps 1.0 2.0 0.0 2.5Explanation / Answer
Ans. The water potential is the sum of solute potential and pressure potential.
Therefore w = s + p . Hence the missing values would be
Cell w p s
A 0.5 0.5 -1.0
B 1.0 1.0 -2.0
C -4.0 4.0 0.0
D -5.0 1.0 4.0
E -2.5 5.0 -2.5
Ans 2 a) The process of transpiration takes place in xylem, it requires large water influx. For water influx the water potential need to be better. Hence cell B would be found in xylem.
Ans 2 b) Cell loses turgor if there is high solute concentration and low water potential, thus cell D is a living cell which has lost turgor.
Ans 2 c) w = s + p, the alternative equation in relation to pressure and osmotic pressure would be
w = P - , the value of = s but in opposite sign, hence the value of = 2
As per van't hoff relation.
= RTC
R = gas constant equals to 2.5 litre-MPa per mole at 250C
T = temperature
C = concentration
hence C = / RT
= 2 / 2.5 * 25
therefore concentratio = 0.032 permoles L-1
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