Demonstrating Osmosis in Potato
This lab will be assessed on DCP and CE
Introduction
Osmosis is the movement of water through a selectively permeable membrane, from a dilute to concentrated
environment. It is a form of passive diffusion. Cells can either take in or expel water across their plasma membranes,
depending upon the conditions of their environment.
Aim
To demonstrate the process of osmosis using potato, and to determine the molarity (concentration) of the cytoplasm of
the potato.
Materials
Potato
test tubes
test tube holder
electronic balance
Paper towel
cork borer
knife/razor blade
distilled water
Sucrose solutions of the following concentrations: 0.1M, 0.2M, 0.5M, 1.0M, 2.0M
250 cm3 beaker
stoppers
filter paper
sticky labels
3
Measuring cylinder 50 cm
Procedure
1. Take 6 test tubes and label them A, B, C, D, E, and F.
2. Measure 40cm3 distilled water using a measuring cylinder and pour into test tube A.
3. Measure 40cm3 0.1M sucrose solution using a measuring cylinder and pour into test tube B. Repeat with the other
concentrations of sucrose solution [0.2M into C, 0.5M into D, 1.0M into E and 2.0M into F].
4. Using a cork borer cut out 6 cylinders of potato of equal diameter and length (approx 3-4cm).
5. Take the mass of each cylinder using the electronic balance and record it.
6. Place one cylinder of known mass into each of the 6 test tubes and stopper.
7. Leave the test tubes in a place where they won’t be disturbed until next lesson.
8. Remove the potato cylinders one by one, pat dry with a paper towel and record the mass using an electronic
balance.
TASKS:
Hypothesis
 Write a hypothesis for what you expect to find in this experiment.
 Cite any sources you use.
Data Collection and Processing
 Record your raw data in a suitable format, including units and uncertainties.
 Process your raw data and present it appropriately, taking into account errors and uncertainties.
Conclusion and Evaluation
 State a conclusion, with justification, based on a reasonable interpretation of the data obtained.
 Evaluate weaknesses and limitations in the procedure.
 Suggest realistic improvements in respect of identified weaknesses and limitations.
Data Collection and Presentation (IB rubric +)
Levels – ISM
(Levels – IB)
ISM Mark
IB Marks
Aspect 1 Recording raw data (table)
(descriptive title, descriptive column and row headers, units,
uncertainties, decimal placing, significant figures.)



Raw data measured as precisely as possible; recorded with same
number of digits after decimal; uncertainties quantified
Raw data recorded in a tidy, organized and properly titled table1
[original data collection sheet was attached to report]
If applicable: diagrams drawn with straight, non-intersecting lines
that terminate exactly at the item being labeled
Aspect 2 Processing raw data
(selection of process, explanation of processing as though to a
non scientist)


All calculations were correct; example calculations were provided
(e.g. mean, standard deviation, Chi-square, etc.)
All the stages - from raw data to final graph – are presented and
can be followed easily
Aspect 3 Presenting processed Data (graph)







Processed data first presented in tidy, organized and properly titled
table(s); exactly two digits after each decimal
Processed data then presented in a graph that clearly shows trends
and allows for easy interpretation
Graph(s) indicated uncertainty with ‘line of best fit’ or error bars
(+/- one standard deviation)
Multiple treatments appeared on same graph for easy
interpretation
Each axis was labeled properly with the correct units (independent
variable on x-axis; dependent variable on y-axis)
Graph titles were complete: included dependent and independent
variables [and species name(s) if applicable]
Avoided unnecessary cosmetic features
1
Exemplary
(Complete)
4
2
Records appropriate
quantitative and
associated
qualitative raw data,
including correct SI
units and
uncertainties where
relevant.
Proficient
(Partial + )
3
1
Records appropriate
quantitative and
associated
qualitative raw data,
including all units
and most
uncertainties where
relevant. Misses 1 or
2 uncertainties.
Processes all the
quantitative raw data
correctly.
Processes most of
the quantitative raw
data correctly.
(Explains all of
processing clearly.)
(Explains most of
processing clearly.)
Presents all
processed data
appropriately and,
where relevant,
includes errors and
uncertainties.
Presents most
processed data
appropriately and,
where relevant,
includes units and
uncertainties on
axes. (Error bars
present but
erroneous)
Developing
(Partial)
2
1
Records appropriate
quantitative and
associated
qualitative raw
data, but with some
mistakes or
omissions.
(Decimal placing
error, significant
figure error, SI unit
error)
Processes
quantitative raw
data, but with some
mistakes or
omissions.
(Limited
explanation of
processing.)
Emerging
(Partial - )
1
1
Records appropriate
quantitative and
associated
qualitative raw data
in appropriate form
without units or
uncertainties.
Not present
(Not at all)
0
0
Does not record any
appropriate
quantitative raw data
or raw data is
incomprehensible.
(Table is difficult to
interpret.)
Processes
quantitative raw
data, but with some
mistakes and some
omissions.
(Confused and
limited explanation
of processing)
No processing of
quantitative raw data
is carried out or
major mistakes are
made in processing.
(No explanation of
processing)
Presents processed
data appropriately,
but with some
mistakes and/or
omissions. (Error
bars absent.)
Presents processed
data in a
comprehensible
format, (omits units
or title is not
descriptive. Axes
may be switched)
Presents processed
data inappropriately
or incomprehensibly.
A table title is numbered and it contains the dependent and independent variables: e.g. Table 1: Volume of O 2 released from potato puree solutions (250ml) at different temperatures (5, 10,
15, 20, 25, 30, 35 oC) following the addition of catalase and H2O2. Each column header contains the units in brackets: e.g. O2 released (ml/min). The units do not repeat in each row of a
column.
Concluding and evaluating (IB rubric +)
Levels – ISM
(Levels – IB)
Exemplary
(Complete)
Proficient
(Partial + )
Developing
(Partial)
Emerging
(Partial - )
Not present
(Not at all)
ISM Mark
IB Marks
4
2
States a valid
conclusion,
with justification,
based on a reasonable
interpretation of the
data. (Compares
value or result with
literature value.)
3
1
States a valid
conclusion,
with weak
justification, based on
a reasonable
interpretation of the
data.
2
1
States a valid
conclusion
based on a
reasonable
interpretation of the
data without
justification.
1
1
States a valid
conclusion to
explain some
limited parts of the
data without
justification.
0
0
States no conclusion
or
the conclusion is
based
on an unreasonable
interpretation of the
data.
Evaluates weaknesses
and limitations. (how
big are the problems?
– quantified))
Identifies weaknesses
and limitations. (how
big are the problems
– qualified)
Identifies some
weaknesses and
limitations, but the
evaluation is weak
or
missing.
Identifies some
weaknesses or
limitations, but the
evaluation is weak
or
missing.
Identifies irrelevant
weaknesses and
limitations.
Suggests realistic
improvements in
respect of all of
identified
weaknesses and
limitations.
Suggests realistic
improvements in
respect of most of
identified
weaknesses and
limitations
Suggests only
Superficial
improvements for
most of identified
limitations.
Suggests some
superficial
improvements for
some of the
identified
improvements
Suggests unrealistic
Improvements or
Does not suggest
improvements
Aspect 1 - Concluding

A valid conclusion was stated clearly as either supporting or not
supporting the hypothesis [eg The data supported the hypothesis
that]

The conclusion was based on: trends in graphs; or comparisons of
different graphs; or comparisons of different lines in the same graph

If applicable, the result was compared with a textbook/internet
source to draw a conclusion about the reliability of the data
Aspect 2 - Evaluating

Sources of error were identified, and for each it was explained how
significantly the error impacts on the reliability of the data

The precision and accuracy of measurements were commented upon
with specific reference to the equipment used

Procedural weaknesses stated with specific reference to: timemanagement, replication, controlled variables, levels of treatment
Aspect 3
Improving the investigation (how can the experiment be made
better)

Realistic and specific suggestions were made to improve each
procedural weakness that was identified