Required Practical 3: Water Potential Flashcards
How do we prepare the potato cylinders so they are exactly the same in this practical? Pieces of apparatus?
- Use cork borer
- Use ruler/ scalpel/ white tile to ensure each of the cylinders are the same length.
What is the risk when cutting potato cylinders with scalpel? What is precaution taken?
- RISK: cutting yourself with the scalpel.
- Precaution: cut away from yourself.
When working out volume of sucrose solution/ water needed to make particular concs of sucrose solution in dilution series, what equation can we use?
C₁V₁= C₂V₂
What is stage 1 of the method of this RP?
DON’T NEED TO KNOW WORD FOR WORD
1.) Label six boiling tubes 0.2,0.4,0.6,0.8,1 moldm-3 sucrose.
2.) Use 1moldm-3 to make up 20cm3 of sucrose solution of concentrations above.
3.) Work out volume of water/ sucrose soltution needed in each boiling tube to make the specific concentration.
What is stage 2 of the method of this RP?
DON’T NEED TO KNOW WORD FOR WORD.
1.) Place boiling tubes containing sucrose solution in water bath.
2.) Slice potato peel of potato/ cut six cylinder chips from potato using borer/ cut them all to same length.
3.) Blot the cylinders dry w/ paper towel.
4.) Record initial mass of each potato cylinder.
5.) Place each cylinder in its boiling tube/ start stop- watch. Give 20mins then remove cylinders from solutions/ blot them.
6.) Reweigh/ record mass of potato cylinders
7.) Calculate change in mass/ then percentage change in mass.
8.) Plot a graph of percentage change in mass against concentration to determine concentration of sucrose that has same water potential as potato cylinders.
Why do we place the boiling tubes with different concentrations of sucrose solutions in a water bath at same temp?
- Because temperature will affect the amount of kinetic energy of water molecules and therefore will affect rate of osmosis.
- So, the temp must be controlled.
Why do we have to cut the potato cylinders to the same length in this practical?
- To ensure that they all have the same surface area.
- Because surface area will affect the rate of osmosis.
- So, surface area has to be controlled.
Why is it important to blot the potato chips/ cylinders dry at the start (before placing them in the sucrose solutions?)
- Ensures that any water outside the cells/ potato will be absorbed so won’t affect initial mass of potato recorded (ie. mass won’t appear larger than it should because excess water hasn’t been removed.)
Why do we calculate a “percentage change in mass” in this experiment?
- Means that the amount of water lost/ gained by potato cells can be compared (it takes into account that we didn’t have the same initial mass of each potato cylinder.)
Where, on our calibration curve, shows the sucrose concentration that has same water potential as the potato tuber cells?
- When there is a percentage change in mass of 0. Where LOBF crosses x axis.
- No gain/ loss of water = isotonic solution (so, concentration of sucrose in potato cells must be same as concentration of sucrose in the solution.)
What is the name of the graph we plot in this RP of percentage change in mass against concentration?
- Called a calibration curve.
Why do we call the cells in this RP “potato TUBER cells?”
- Tuber–> shows that it is inside the potato ie. not including the epithelial cells as we removed skin using scalpel.
After we have found the concentration of sucrose solution that has the same water potential as the potato tuber cells, how do we work out this actual value of water potential?
- We use a conversation table to look up the conversion of moldm⁻³ to water potential.
If I was given conc of sucrose stock solution/ volume of stock solution and used C1 V1 to calculate the V2 (given C2 - concentration of solution you WANT to make), is V2 just the volume of sucrose?
- No. V1 is the volume of sucrose + water together
- Ie. V2 = V1 + volume of water you have distilled it with
