Estimating Osmolarity of Plant Cells
Criteria Assessed: DCP
Introduction
In this experiment you will be estimating the osmolarity of potato cells by finding their
change in weight in solutions of known molarity. The object is to find the molarity where
the mass does not change. No net change in weight indicates that there has been no net
gain or loss of water. This is a means of indirectly finding the osmolarity of the cells
themselves.
Apparatus
1 large potato
Petri dish
7 x 250 ml beakers (disposable cups may be substituted)
sucrose solutions: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 molar
marker
razor blade/scalpel
forceps
cork borer
balance (2dp)
distilled water
paper towels
ruler (30 cm)
Method
1. Get 100 ml of each of the solutions including distilled water. Place the solutions
into the 250 ml beakers, and label them including your group names.
2. Use the cork borer to obtain seven complete potato cylinders at least 5.5 cm long.
3. Using the razor blade cut all the cylinders to a uniform length approximately 4.5 cm
long, making sure to remove the skin from the ends in the process.
4. Place all the cylinders into a Petri dish and cover to prevent drying out.
5. Remove a cylinder and cut into discs about 5mm thick using the razor blade.
6. Remove excess water from the discs by blotting them with paper towel.
7. Weigh the discs on the balance.
8. Transfer the discs to the water beaker. Make sure not to lose any discs.
9. Repeat steps 5-8 with each cylinder, placing the discs into the appropriate
solutions.
10. After waiting several hours to one day, remove all the discs from the water beaker.
Blot the discs, and weigh.
11. Weigh the discs from all the solutions. Making sure not to lose any discs.
Lab Report
 Write-up DCP only. The focus here is to practise your DCP skills, particularly graph
drawing.
 There are deliberate omissions and short-comings in the method; CE may also be
practised with this in mind.
 Alternatively discuss short comings before attempting a full (D, DCP and CE) or design
only lab on a different aspect of osmosis.