Required practical 3 Flashcards
Osmosis potato practical
What occurs when plant tissue is placed in a hypotonic solution
Hypotonic is where the water potential of the plant is lower than that of the solution
Water will move into the plant cell by osmosis, causing it to expand and increase in mass
What occurs when plant tissue is placed in hypertonic solution
Hypertonic solution is where the water potential of the plant is higher than that of the solution
As a result, water moves from the plant to the solution by osmosis, so mass of the plant decreases and it may shrivel up.
What is this practical finding out
. It produces a calibration curve to identify the water potential of plant tissue, but we are using potato tubers.
Describe the steps of this practical: How to prepare the dilution series using sucrose
. Label 6 boiling tubes 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 moldm-3
. Use the 1.0 moldm-3 sucrose solution and distilled water to make up 20cm3 of sucrose solution in each of the following concentrations:
- 0.2mol
- 0.4 mol
- 0.6 mol
- 0.8 mol
- 1.0 mol
Since the volume of each will be 20cm, do the expected concentration multiplied by 20 to find the amount of sucrose solution needed to be added.
Eg 0.2 X 20 is 4 so add 4cm of sucrose and 16cm of water
Once you have the dilution series, what do you do in the practical
. Put the boiling tubes containing different concentrations of sucrose solution in a water bath at 30 degrees (use thermometer to check that the temperatures in each tube reach this)
. Using a potato cutter, cut 6 chips from your potato, removing any peel from the potato.
Then use ruler, scalpel and tile to make all the chips the same length. Gently blot to remove excess water
. Put each potato chip on a piece of paper towel labelled with the same conc as the test tubes
. Then weigh each potato chip and record masses
. In water bath, quickly put each potato from each labelled square into the corresponding test tube
. Leave for 20 minutes, then remove chips from tubes, Blot dry with paper towel and dab until each is dry. DON’T SQUEEZE CHIPS.
Then reweigh.
. Calculate change in mass and so then the percentage change in mass
What is a calibration curve
Graphs used to determine an unknown concentration of a sample by comparing the unknown to a set of standard samples with known concentrations
Use a dilution series to get the known concentrations
Why are the potatoes left in water bath for 20 minutes
To allow time for osmosis to occur until plant tissue reaches equilibrium with the solution surrounding it
What is water potential determined by
. The concentration of solutes
eg the higher the solute concentration, the lower the water potential
Why is percentage change calculated rather than change in mass
The potatoes will have different starting masses, so percentage change allows us to compare them
Why are the potatoes dabbed dry after the sucrose solution
. To remove any excess water clinging to its surface which will increase its mass
Controlled variables of practical
. Volume of sucrose solution
. Size of potato chips
. Temperature of solution in water bath
. Time they’re left in solution
What does the graph for this practical look like
When the line of best fit crosses the x axis, what does this mean
Plot concentration of sucrose solution on x axis, and have change in mass on y axis
This is the point where the solution is isotonic, so it has the same concentration of sucrose as the potato, so no water will move in or out of it by osmosis
What can we conclude from the results
. Potato chips in solution with lower concentrations of glucose will increase in mass and vice versa
. Because in the more dilute solutions, the solution has a higher water potential than the potato so water will move into the potatoes, increasing the mass of them
