Investigating Water Potential Flashcards
Purpose of calibration curves?
Determine the concentration of an unknown sample by comparing to a set of standard values with known concentrations
How is a calibration curve used to find the concentration of plant tissue
Plot a calibration curve of percentage change in mass against concentration. Find X intercept where the plant tissue is isotonic to the sucrose solution
What occurs when plant tissue is placed in a hypotonic solution?
Water moves into plant tissue by osmosis, plant tissue increases in mass
What occurs when plant tissue is placed in hypertonic solution?
Water moves out of the the plant tissue by osmosis plant tissue decreases in mass
Why is the potato left for 20 mins?
To allow for osmosis until the plant tissue reaches equilibrium with surrounding solution
What is water potential determined by?
Concentration of solutes, the higher the solute concentration the lower the water potential
Procedure?
- Make a simple dilution of 1M sucrose to produce 5 concentrations. Add 5cm cubed to 5 different test tubes
- Cut a potato into equal sized chips and weigh
- Place a chip in each test tube and leave for 20 mins
- Take out and dab excess water weigh them
- Calculate percentage change in mass
Why is the percentage change used rather than the actual change in mass?
Potato chips may not all have the same starting mass, and allows for comparison
What is indicated by the x intercept of the calibration curve?
The concentration that is isotonic to the solution tested
Explain change in mass
The potato chips with concentration lower ( high water potential) than the sucrose solution lose mass as there is a net movement of water out of the cell. The potato chips with higher concentration ( lower water potential) that the sucrose solution gain mass as there is a net movement of water into the cell
CV
Volume of sucrose solution
Size of chips
Length of time in solution
