Required Practical 3- Water Potential Of Plant Tissue Flashcards
What is a calibration curve?
Graphs used to determine unknown concentration of sample by comparing unknown to set of standard samples with known concentration
Why is it important that all samples from same plant tissue
Standardise test- different plant tissues could have different water potentials
Why is cork borer used to cut samples
Provide constant area
Why is sucrose solution used to determine water potential of plant tissue
-Sucrose molecules too large to pass through cell surface membrane
-So change in mass of samples due to osmosis
Why are bungs placed on top of sucrose solutions?
Prevent evaporation of sucrose solutions
Why is potato skin removed?
Skin prevent passage of water in and out of cells- ensures osmosis can occur
Why are samples blotted before weighed?
Remove excess water (moisture) - could alter weight
Important not to squeeze samples when dry?
So water not removed that entered by osmosis
How to determine water potential of plant tissue?
-plot calibration curve
-interpolate when percentage change in mass =0
-convert concentration of solution to water potential
Why do the masses not have to be identical at the start of the experiment?
Percentage mass is calculated so comparisons can be made
Why is potato disc left in solution for 20 minutes?
To allow time for osmosis until the plant tissue reaches equilibrium with its surrounding solution.
Outline procedure of investigating osmosis
1.Make a simple dilution of 1M sucrose to produce 5
concentrations. Add 5 cm3 to 5 different test tubes.
2. Cut a potato into equal sized chips and weigh.
3. Place a chip in each test tube and leave for 20 minutes.
4. Take out. dab the excess water and weigh them again
5. Calculate the percentage change in mass
Control variables
-volume of sucrose solution
-size of potato chip
-length time left in solution
-dab each potato disc with paper towels
