OSMOSIS LAB REPORT
NAME
TITLE 1: DETERMINATION OF THE WATER POTENTIAL OF WHITE POTATOES
(TUBEROSUM SOLANUM), USING SUCROSE SOLUTION AS A REFERENCE
POINT
TITLE 2: AN INVESTIGATION OF THE EFFECT OF SUCROSE SOLUTION
CONCENTRATION (%) ON THE RATE OF OSMOSIS IN WHITE POTATOES
(TUBEROSUM SOLANUM)
INTRODUCTION
We have learned in class that water moves in and out of cells through the process of
osmosis. Water moves by osmosis down a eater potential gradient, from a high
water potential to a low water potential1. The water potential of Swiss white
potatoes (Solanum Tuberosum) is not known, whereas the water potential of 1M
sucrose solution is well known (1 M Sucrose @ 20 C = -2.436 MPa, 50% sucrose =
0.146 moles of sucrose2).
We would expect that when potato cells are hypertonic relative to sucrose solution,
water will move by osmosis from the sucrose solution into the potato cells, resulting
in an increase in mass of the potato cells. Conversely, we would expect that when
potato cells are hypotonic relative to sucrose solution, water will move by osmosis
from the potato into the sucrose solution, resulting in an decrease in mass of the
potato cells. At the point of isotonicity, where the water potential of the potato
cells is equal to the water potential of the sucrose solution, there will be no net
movement of water from potato to sucrose solution, or vice versa.
Identifying the point of isotonicy will enable identification of the water potential of
the potato cell.
The rate of osmosis will be determined by calculation of the % mass change in
potato chunks of similar size and mass, submerged for 24 hours in sucrose solutions
of varying concentration.
1
2
IGCSE Coursebook, Second Edition, Editors M. and G. Jones 2010 p. 25 - 30
http://plantphys.info/plant_physiology/osmosis.shtml Accessed 1.10.13
PROCEDURE
VARIABLES
Independent
Dependent
Controlled
Sucrose concentration (%, ± 0.1%)
% change in potato mass after 24 h(%,
± 0.1%)
Factors which could influence the rate
of osmosis:
 Ambient temperature (experiment
will be carried out in a climatecontrolled environment)
 Surface area: potato chunk cutters
will be used in order to produce
chunks of approximately uniform
size
1. Potato chunks of similar size were cut using a custom designed potato chunk
cutter, and their mass recorded in a data table using a balance accurate to
0.01g.
2. Having measured and recorded their mass, two potato chunks were put into
each of 5 test tubes, labelled distilled water, 1%, 10%, 25% and 50% sucrose
respectively.
3. The potato chunks were submerged in sucrose solution of the appropriate
concentration, and left submerged for 24h. The tops of the test tubes were
covered using rubber bungs to prevent evaporation of the solution.
(Illustration, Figure 1)
4. After 24 h, the potato chunks were removed from their respective solutions,
dried carefully using paper towel, and their mass determined using the same
electronic balance.
5. The % change in mass was calculated using the formula:
6. % change in mass = (initial mass – final mass) X 100
initial mass
Figure 1: Illustration of experimental procedure: potato chunks of known mass
were submerged in sucrose solution of defined concentration for 24 h.