Effects of Osmosis on Living Tissue
Purpose: to measure the amount of osmosis potato tissue
experience in different concentrations of sugar solution.
Background information: notes on cell transport, cell membrane
and types of solutions – hypertonic, hypotonic, isotonic. Note – sugar
molecules are too large to pass through a potato cell membrane.
Materials: plastic cups (6)
distilled H2O
potato cores (2 per [ ]
ruler
dissecting razor/scalpel
marking pencil
Sugar solutions (0.2, 0.4, 0.6, 0.8, 1.0)
electronic balance
weighing boats
tweezers
grad cylinder
Procedure: Work in groups to acquire data but all labs will be
individual work
1. Obtain 6 plastic cups and label the top with the six different
concentrations.
2. Add approximately 50 mL of each solution into the appropriate
cups – Hint measure one solution and use it to fill the other cups
3. Obtain 12 cylinders of potatoes. Cut them so they are all the
same length using the razor blade – should be at least 2.5 cm
long. The longer the better.
4. Divide the cores into 6 groups and blot them dry with paper
towels. Take a picture. Note the flexibility of the cores.
5. Using the weighing boats, find the mass of the different groups,
making sure to record to the uncertainty of the machine.
6. At the same time, place the potato cores into the appropriate
cups, take a picture, and leave them for 24 hours. Place them
somewhere where they will not be disturbed. Decide who will
come to record the second day data.
7. Start setting up your table in excel. Title (not the lab title)
independent variable first column. For dependent variable, it will
be the final mass and then you will calculate the percent mass
change. To find this, use the following formula; (final mass –
initial mass)/initial mass x 100.
8. In 24 hours, you will remove the cores using the tweezers, blot
them dry and calculate their mass. Take a picture.
9. Record observations.
10. Once you are sure you are done, the potatoes go in the
garbage, the cups are washed and dried, the razor/scalpel is
washed and dried and all equipment returned.
Requirements:
1. problem (given) and proper hypothesis
2. independent and dependent variables and 3 good variables to
control with reasons why they need to be controlled
3. A brief recap of the procedure, in paragraph form, with pictures
supporting the explanation
4. proper table and observations
5. graph with line of best fit (it will involve negative and positive
numbers)
6. analysis the graph by stating the relationship and what that
means
7. on a separate page, answer the following questions
8. Note that I will be evaluating your lab skills in this lab – whether
you are prepared, know what you are doing, stay on task, work
with others, know how to use equipment properly and safely. See
rubric below.
Questions
1. From your observations, is there any evidence to suggest that
water has entered the potato cells? Explain.
2. What is the slope line of your graph showing, what is the trend?
3. When the slope line crosses the zero point, what does this
mean?
4. From you data, how can you determine the water concentration
of the potato. Explain.
5. Which would provide more reliable data, the class average or
your own group’s data? Explain
6. When food is pickled, as much water as possible must be
removed from the cells. How would you accomplish this?
On the next page, are the parts of the lab checklist that you will
be graded on. Note – is on wiki. If you have a problem, make
sure you consult at my lab write up doc first.
Each of the aspects will be marked on a scale of 0-3.
3 = exceeds expecations expected at this level
2 = meets expections at this level
1 = partially meets expections, some work required
0 = does not meet expections
Problem/Question

My hypothesis includes my reasoning and contains specific
quantitative/measureable expectations which may be based on
models (where applicable)
Designs a method



I have listed the independent and dependent variables – realizing
that there can only one of each and (I’ve been given a brief
statement of their relationship) in hypothesis instead?
I have listed the important variables to control and stated why
they need to be controlled (expanded in the procedure if
necessary) A control group is described where needed
I have written a clear, logical method that is sequential in order
and repeatable by others
Collection and presentation of data


I have presented the appropriate data in a suitable format that is
easy to interpret and logical to follow. It is word-processed or in
Excel and any necessary additional observations are included
I have set up any tables properly; descriptive title, independent
variable first column, column headings, units with uncertainty, all
data shown and compliments uncertainty. If drawings used;
descriptive title, in pencil, appropriate size, labels correctly drawn
and explanations where needed
Data processing


I have processed the correct data appropriately, shown formulas
with worked examples of the processing and used proper number
of decimal places in calculations
I have used some method of summarizing the processed data,
preferably as a graph. For graphs; correct type used, descriptive
title, averages used, axis labeled and units given, variables on
correct axis, line of best fit were appropriate, ability to manipulate
excel or similar program used for graphing.
This is the rubrics I will use for lab skills.
Rubrics for lab skills
Excellent = skill is observed all the time and at an above average standard level
Good/very good – skill is observed most of the time and/or at an average or above
average standard level
Fair = skill is observed only some of the time and/or at an average or below average
standard level
Below standard = skill is rarely or never observed and/or at a below standard level
Name ___________________________________________________
Skill
Preparation
Follows
instructions
Carrying out
techniques
Safety and
techniques
Work ethic
Excellent
Obviously read
the lab
through, asks
pertinent
questions
Follows
instructions
accurately,
adapts to new
circumstances
Competent and
methodical in
the use of
techniques and
equipment
Consistently
uses standard
equipment
safely as
instructed
Works
effectively and
efficiently with
their group and
by themselves
V Good - Good
Appears to understand
the lab, asks some
needless questions
Fair
Doesn’t really
understand the lab,
asks a lot of needless
questions
Below standard
Not prepared to work,
wastes time as is so ill
prepared
Follows instructions
but requires
assistance
Follows most
instructions and/or
requires supervision
Rarely follows
instructions and
requires constant
supervision
Usually competent and Sometimes competent Rarely competent or
methodical in most
and/or not methodical methodical in
techniques/equipment in
techniques/equipment
techniques/equipment
Generally uses
standard equipment
safely as instructed
Uses standard
equipment safety
under supervision
Requires constant
supervision, has little
regard to safety
Mostly works
effectively and
efficiently, minimal
non work interaction
Generally works
effectively but not
efficiently, some group
interaction
Gets little work done
in time period and/or
a lot of non work
interaction