RP 3 - production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue

Question 1

describe how a dilution can be calculated

Answer 1

1) calculate dilution factor = desired conc / stock conc
2) calculate volume of stock solution = dilution factor x final desired volume
3) calculate volume of distilled water = final desired volume - volume of stock solution

Question 2

describe a method to produce of a calibration curve with which to identify the water potential of a plant tissue ( potato) (part 1)

Answer 2

part 1 : collecting data
1) create a series of solutions using a 1moldm-3 sucrose solution
CONTROL : volume of solution
2) use sample to cut a potato into identical cylinders
CONTROL : size , shape and surface area of plant tissue and source of plant tissue (age)
3) blot dry with a paper towel and measure inital mass of each piece
CONTROL : blot dry to remove excess water before weighing
4) immerse one chip in each solution and leave for a set time in a water bath
CONTROL : length of time in solution , temperature, regularly stir
5) Blot dry with a paper towel and measure final mass of each pieces
CONTROL :
Blot debt remove excess water before weighing
Repeat 3 more times at each concentration

Question 3

describe a method to produce of a calibration curve with which to identify the water potential of a plant tissue ( potato) ( part 2)

Answer 3

part 2 processing data :
6) calculate % change in mass ( final -inital mass ) / initial mass
7) plot graph with concentration on x axis and percentage change in mass on y axis ( calibration curve )
- must show positive and negative regions
8) identify concentration where line of best fit intercepts x axis
water potential of sucrose = water potential of potato
9) use a table to find the water potential of that solution

Question 4

explain why % change in mass is calculated (2)

Answer 4

enables comparison
as plant tissues samples had different initial masses

Question 5

explain why the potatoes are blotted dry before weighing (2)

Answer 5

• solution on surface will add to the mass
• amount of solution on cube varies

Question 6

explain the changes in plant tissue mass when placed in different concentrations of solute

Answer 6

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