required practical 3 Flashcards
what is required practical 3
production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue
aim of practical 3
Calibration curves are graphs used to determine an unknown concentration of a sample by comparing the unknown to a set of standard samples with known concentrations - they are also known as standard curves.
A dilution series can be used to create a set of samples with known concentrations.
A calibration curve can be used to determine an unknown water potential in a potato sample.
Water potential is the tendency of water to diffuse from one area to another.
Water molecules move from areas of high water potential to areas of low water potential by osmosis.
The water potential is determined by the concentration of solutes.
The movement of water in and out of cells is related to the relative concentration of solutes either side of the cell membrane.
3 equipment list
● Potato tuber
● Cork borer
● Scalpel
● Ruler
● Distilled water
● Sucrose solution (1M)
● Boiling tubes
● Boiling tube rack
● Timer
● Digital balance
● Paper towels
3 method
- Make a series of dilutions of 1M sucrose solution. These should be at 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0M sucrose. Dilute using distilled water.
- Measure 5cm3 o f each dilution into separate test tubes.
- Use a cork borer to cut out six potato chips and cut down the sections into
identically sized chips. Dry each chip using a paper towel to remove excess
water but do not squeeze. - Weigh each before the start of the experiment.
- Place a potato chip in each test tube (one per sucrose concentration) and leave
for 20 minutes. - Remove each potato chip, dry gently using paper towel, and weigh them in turn.
- Calculate the percentage change in mass for each sucrose solution.
3 risk assessment
scalpel
broken glass
3 graph
● Plot a graph of change in mass against concentration of sucrose solution.
● The point at which the line of best fit crosses the x axis (zero change in mass)
indicates the point at which the solution is isotonic. This is when the water potential of sucrose solution is the same as the water potential of the potato tissue, so there is no net movement of water in or out of the potato.
3 conclusion
● Potato chips in lower concentrations of glucose solution will increase in mass, whilst those in the higher concentrations of glucose solution will decrease in mass.
● In the dilute glucose solutions, the solution has a higher water potential than the potato, so water passively moves via osmosis to the area of lower water potential (the potato). This causes the potato to increase in mass.
● In concentrated glucose solutions, water will move out of the potato, thus the potato will decrease in mass
