Describe how to calculate dilutions
C1 x V1 = C2 x V2
● C1 = concentration of stock solution
● V1 = volume of stock solution used to make new concentration
● C2 = concentration of solution you are making
● V2 = volume of new solution you are making
V2 = V1 + volume of distilled water to dilute with
Describe a method to produce of a calibration curve with which to identify the water potential of plant tissue (eg. potato)
- Create a series of dilutions using a 1 moldm-3 sucrose solution (0.0, 0.2, 0.4, 0.6, 0.8,1.0 mol dm-3)
● Volume of solution, eg. 20 cm3 - Use scalpel / cork borer to cut potato into identical cylinders
● Size, shape and surface area of plant tissue
● Source of plant tissue ie variety or age - Blot dry with a paper towel and measure / record initial mass of each piece
● Blot dry to remove excess water before weighing - Immerse one chip in each solution and leave for a set time (20-30 mins) in a
water bath at 30oC
● Length of time in solution
● Temperature
● Regularly stir / shake to ensure all surfaces exposed - Blot dry with a paper towel and measure /
record final mass of each piece
● Blot dry to remove excess water before weighing
Why calculate % change in mass?
● Enables comparison / shows proportional change
● As plant tissue samples had different initial masses
Why blot dry before weighing?
● Solution on surface will add to mass
● Amount of solution on cube varies
Explain the changes in plant tissue mass when placed in different concentrations of solute: increase in mass
● Water moved into cells by osmosis
● As water potential of solution higher than inside cells
Decrease in mass
● Water moved out of cells by osmosis
● As water potential of solution lower than inside cells
No change
● No net gain/loss of water by osmosis
● As water potential of solution = water potential of cells
