Osmosis & Diffusion Lesson Plan
Class and grade level: Biology 2, 11th and 12th
Period: 5
(http://www.msu.edu/~lupalisa/webplans/biologyunits/lessoncalendarlog.htm)
Knowledge: Big Ideas
The general tendency of molecules is to move from an area of higher concentration to
one of lower concentration. As this constant movement occurs, molecules “bump” into each
other, accelerating this movement more. Such distribution happens more quickly as the
temperature increases, as heating causes the molecules to move faster and make more
frequent contact. A special case of the movement of water across a concentration gradient
occurs when a semi-permeable membrane (such as that bordering cells) appears; this process
is called osmosis. For a cell present in an isotonic solution (where the concentration of water
on both sides of the membrane is the same), the cell maintains a steady, normal shape. If the
concentration of water relative to other dissolved substances is lower inside the cell (hypotonic)
than outside, the water outside will enter the cell and cause the cell to expand. If just the
opposite (hypertonic), water molecules will exit the cell to enter the more concentrated solution
outside, and the cell will shrink.
Knowledge: Experiences, Patterns, and Explanations
Observations or
experiences (examples,
phenomena, data)


Kool aid in cold or warm
water
Raisin in water
Celery in deionized water
Celery in salt water
Baggie with iodine solution
placed in starch solution
Baggie with iodine solution
placed in iodine solution
Sucrose lab (see lesson)


Kool aid in cold water
Kool aid in hot water





Patterns (laws,
generalizations, graphs,
tables, categories)
Substances (usually water)
move from where ever there is
more to where there is less.
Substances move faster when
the environment is warmer.
Explanations (models,
theories)
The general tendency of molecules
is to move from an area of higher
concentration to one of lower
concentration. As this constant
movement occurs, molecules
“bump” into each other, accelerating
this movement more. A warmer
environment causes molecules to
move faster and make more
frequent contact. A special case of
the movement of water across a
concentration gradient occurs when
a semi-permeable membrane (such
as that bordering cells) appears; this
process is called osmosis. For a cell
present in an isotonic solution, the
cell maintains a steady, normal
shape. If the concentration of water
relative to other dissolved
substances is lower inside the cell
than outside, the water outside will
enter the cell and cause the cell to
expand. If just the opposite, water
molecules will exit the cell to enter
the more concentrated solution
outside, and the cell will shrink.
Application: Model-based Reasoning
Inquiry: Finding and Explaining Patterns in Experience
Practices: Objectives for Student Learning
Objective
Michigan Objectives
1. Compare and contrast ways in selected cells are specialized to carry out
particular life functions.
2. Explain how living things maintain a stable internal environment.
Specific Topic Objectives
1. Use knowledge of diffusion to explain how substances move from areas of
higher concentration to areas of lower concentration.
2. Use knowledge of diffusion and osmosis to explain how substances move
across a membrane.
Type
Using
Using
Using
Using
1. Beaker of cold water and a packet of bright colored kool aid
2. Beaker of hot water and a packet of the same bright colored kool aid
3. Beaker of room temperature water and a few raisins (should have sat for a few
hours)
4. Beaker of raisins
5. Beaker of deionized water with celery in it
6. Beaker of salt water with celery in it (should have sat for 24 hours)
1) As students come in, have them look at the demonstrations (1, 2, 4 & 5) and predict
what will happen if kool aid is added to cold water, kool aid is added to hot water, a
raisin is put in water, and if salt is added to the water that a stalk of celery is in. They
should do this on their handout under the predictions section. 5 minutes
2) Run demonstrations (put kool aid into cold and hot water beakers) and/or pull out after
demonstrations (3 & 6). Explain what each looks like and allow students to come up
and look at them.
3) Students individually work on handout that corresponds to demonstrations. 30
minutes
4) Class discussion about predictions, drawings, and explanations of demonstrations.
15 minutes
5) Prepare for sucrose lab and have students make predictions about the lab outcome.
40 minutes
6) Predictions are homework for Wednesday – come in ready to analyze lab data.
Due date: _________________
Name:_______________
Predictions for Demos
Predictions are educated guesses. They are not meant to be looked at as right or wrong.
Using your brain and things that you have learned in this class, please make predictions about
the following demonstrations and write them below. The more detail and explanation, the
better.
Kool aid in cold water:
Kool aid in hot water:
Raisin in water:
Salt added to water solution for celery:
Dissolving Kool Aid
(Class demonstration)
Part I: The Drawings
1. Start with a drawing of the situations that includes all the relevant parts in each of the two
conditions (kool aid in cold water, kool aid in hot water): cup and representative molecules
making up the water and kool aid.
2. Draw the pattern of movement of molecules initially and at the end of a few minutes for
each condition.
Part 2: The Explanation
3. Write the first part of the explanation: A sentence or two illustrating the concentration of the
molecules making up the kool aid in each condition.
4. Write the second part of the explanation, i.e., a sentence or two describing the pattern of
movement of molecules and their eventual distribution in the cold and hot water. The
explanation should include what happens to the kool aid and water as a result of the
movement of these molecules.
Plump Raisin
(Class demonstration)
Part I: The Drawings
1. Start with a drawing of the situations that includes all the relevant parts in each of the
conditions (raisin out of water, raisin in water): cup and representative molecules making up
the water and raisin.
2. Draw the pattern of movement of molecules initially and at the end of a few minutes for
each condition.
Part 2: The Explanation
3. Write the first part of the explanation: A sentence or two illustrating the concentration of the
molecules making up the raisin in each condition.
4. Write the second part of the explanation, i.e., a sentence or two describing the pattern of
movement of molecules and their eventual distribution in the air and water. The
explanation should include what happens to the raisin and water as a result of the
movement of these molecules.
Wilting Celery
(Class demonstration)
Part 1: The Drawing
1. Start with a drawing of the situation that includes all the relevant parts in each of the two
conditions (celery in distilled water, celery in salt water): beaker, celery, representative
molecules making up solutions inside and outside the celery.
2. Draw the pattern of movement of molecules initially and at the end of a few minutes.
Part 2: The Explanation
3. Write the first part of the explanation: A sentence or two illustrating the concentration of the
molecules making up the solutions inside and outside the celery.
4. Write the second part of the explanation, i.e., a sentence or two describing the pattern of
movement of molecules and their eventual distribution inside and outside the celery. The
explanation should include what happens to the cells making up the celery as a result of the
movement of these molecules.
Predictions for Lab
Please make predictions about how the mass of each sucrose bag will change (it may or may
not change). + means the mass of the bag will increase. 0 means there is no change in mass.
– means the mass of the bag will decrease. Also indicate your reasons for each prediction.
Table 1: Change in dialysis bag mass predictions
Contents in dialysis bag
Change in mass
Reasoning
(+, 0, -)
a) Distilled water
b) 0.2 M sucrose
c) 0.4 M sucrose
d) 0.6 M sucrose
e) 0.8 M sucrose
f) 1.0 M sucrose
Due date:_____________
Name:_______________
Sucrose Laboratory Investigation
Overview: In this lab investigation, you will work with sucrose solutions of varying molarities.
Molarity is a measure of the concentration of a substance in a solution (mol/L). As the molarity
increases, the concentration of sucrose increases. In this investigation you will determine the
percent change in mass of dialysis bags each with a different sucrose molarity. In addition you
will construct a graph and describe the relationship between percent change in mass and
molarity.
Objectives: As a result of this lab, you should be able to describe solutions as hypertonic,
hypotonic, or isotonic. You should also be able to use knowledge of diffusion and osmosis to
explain how substances move across a membrane. You should also be able to apply these
concepts to the maintenance of a stable environment in living things.
Introduction: Recall that cell membranes are made of a phospholipids bilayer, with polar and
nonpolar regions. In order for things to move in and out of the cell, they must pass through this
membrane. The ability of molecules to move across a cell membrane depends on two things:
(1) the permeability of the membrane and (2) the type of molecule that wants to get through.
The cell membrane is selectively permeable. In other words, it only allows the passage of
some substances and not others. Membranes that are more permeable allow more types of
molecules through while less permeable membranes allow fewer types of molecules through.
The cell’s goal is to maintain a stable internal environment, or homeostasis. Diffusion is the
movement of molecules from high concentration to low concentration, or down its concentration
gradient. Since energy is NOT required this is called passive transport. More specifically,
osmosis is the diffusion of water down a concentration gradient. Movement of molecules
continues until a concentration balance between the two areas is reached.
Selectively permeable membrane
HIGH CONCENTRATION
LOW CONCENTRATION
Materials (per group):

6 15-cm strips of
presoaked dialysis
tubing

Funnel

Deionized water



6 – 100 mL beakers
or cups
Pre- made sucrose
solutions
12 pieces of dental
floss

Tap water (faucet)

50 mL beaker
Procedure:
1. Obtain 6 15-cm strips of presoaked dialysis tubing.
2. Tie off one end of your piece of dialysis tubing with dental floss to form a bag. Using the
funnel, pour 10mL of distilled water into this bag.
3. Remove most of the air from the bag by drawing the dialysis bag between two fingers.
Tie off the other end of the bag leaving sufficient space in case of expansion of the
contents of the bag.
4. Repeat steps 2 & 3 five times filling each bag with 10mL of 0.2M, 0.4M, 0.6M, 0.8M, or
1.0M sucrose instead of distilled water. See diagram below.
Distilled water
10 mL
0.4 M sucrose
10 mL
0.8 M sucrose
10 mL
0.2 M sucrose
10 mL
0.6 M sucrose
10 mL
1.0 M sucrose
10 mL
5. Rinse each bag with tap water to remove any sucrose spilled during filling.
6. Carefully blot the outside of the bag and record its initial mass (grams) in Table 1.
7. Fill a 100 mL beaker or cup two-thirds full with distilled water. The beaker or cup should
be labeled with your table # and the molarity of the solution in the bag.
8. Immerse the bag in the beaker of distilled water.
9. Repeat steps 5 – 8 with the other 5 bags and cups.
10. Let stand for 30 minutes or more.
11. Carefully blot the bag and determine its mass (do this one bag at a time).
12. Record the date in Table 1. Blot, mass, and record the data for each bag.
13. Graph the results in Graph 1. Provide a title, labeled x and y axis with units, and a
key.*Think : what is the molarity of the distilled water?*
14. Determine the mass differences and record them in Table 1.
Mass difference = Final bag mass – initial bag mass
15. Calculate the percent changes in mass and record them in Table 1.
Percent change in mass = Final bag mass – initial bag mass X 100
Initial bag mass
16. Answer the analysis questions
Table 1. Dialysis bag results
Contents of dialysis
bag
Distilled water
0.2 M sucrose
0.4 M sucrose
0.6 M sucrose
0.8 M sucrose
1.0 M sucrose
Initial bag
mass (g)
Final bag
mass (g)
Mass difference
(g)
Percent change
in mass (%)
Analysis Questions:
1. How did your predictions compare to your experimental data? (Discuss each solution)
2. Explain the relationship between the increase in mass of the bag and the molarity of the
sucrose within the dialysis bags? Why does this relationship exist?
3. Why did you calculate the percent change in mass rather than simply using the change in
mass?
4. Predict what would happen in an experiment if all the bags were placed in a 0.6 M sucrose
solution instead of distilled water. Discuss each solution.
5. Classify the solution in each dialysis bag as hypotonic, hypertonic, or isotonic compared to
the distilled water in the cup. How did you determine each of these?
6. Some bags gained mass. What is this extra mass? Where did it come from? Why did it
come into the bag (how does it know to go in)?
7. Silly Sally forgot to label each beaker with the corresponding bag’s sucrose molarity. How
could you determine which bag contained which sucrose molarity?
Now that you understand osmosis, can you apply what you’ve learned? 
8. If human cells are hypotonic to sea water (salt water), why is drinking sea water for
an extended period of time dangerous?
9. Why is salt used to free leaches from your skin?
10. If you drink an entire gallon of water, it is not all eliminated through urine. Where did the
water go and why?