RP3 Investigating Water Potential Flashcards
What is the purpose of calibration curves?
They are used to determine the concentration of an unknown sample by comparing it to a set standard of values with known concentration.
How is a calibration curve used to find the concentration of plant tissues?
Plot a calibration curve of percentage change in mass against concentration. Find the x- intercept where the plant tissue is isotonic to the sucrose solution.
How is the calibration curve used to find the concentration of plant tissue?
Plot a calibration curve of percentage change in mass against concentration. Find the 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 the plant as there is a high water potential outside the cell (less sugar), plant tissue increases in mass.
What occurs when plant tissue is placed in a hypertonic solution?
Water moves out the plant tissue by osmosis, plant decreases in mass.
why are the potatoes disks left in solution for 20 minuets?
To allow time for osmosis until the plant tissue reaches equilibrium with its surrounding solution.
What is water potential determined by?
Concentration of solutes. Higher solute concentration the lower the water potential.
Outline the procedure of investigating osmosis using potatoes tissue.
- Make a simple dilution of 1M sucrose to produce 5 concentrations. Add 5cm3 to 5 different test tubes.
- Cut potato into equal sized chips and weigh.
- Place chip in each test tube and leave for 20minuets.
- Take out, dab the excess water and weigh them again.
- Calculate the percentage change in mass.
Why is percentage change used rather than the actual change in mass?
Potato chips may not all have the same starting mass.
Percentage change allows comparison.
What is indicated by the x-intercept of the calibration curve?
The concentration that is isotonic to the solution tested.
Explain the change in mass in the potato chips.
The potato chips with concentration Lowe than sucrose solution (high water potential) lose mass as there is a net movement of water out of cells.
The potato chips with concentration higher than sucrose solution (low water potential) gain mass as there is a net movement of water into the cell.
Why are the potato chips dabbed dry after removing from sucrose solution?
To remove excess water clinging to its surface.
What are the controlled variables of this practical?
- volume of sucrose solution
- size of potato chips
- length of time left in solution
- dab each potato disc with paper towels
