Sinclair STEM Grant
Teacher Instructions/Lesson Plan Template
TITLE OF LESSON/MODULE
Cell Size and the Rate of Diffusion/Osmosis
AUTHOR(S) AND SCHOOL AFFILIATION(S)
Michelle Wysong, Kings High School
OVERVIEW
This module will allow students to investigate and understand how cell size affects the rate of diffusion and
osmosis. This will help students develop an understanding of why cells are so small, and how size determines how
quickly a cell can absorb the required nutrients or eliminate wastes.
TYPE/LEVEL OF INQUIRY 1= Open Inquiry
3= Guided Inquiry
2 = Open/Guided Inquiry
GRADE LEVEL/COURSE
11/12 AP Biology
ANTICIPATED LENGTH OF LESSON/MODULE (MINUTES)
150 Minutes (3 classes)
PREREQUISITE KNOWLEDGE
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Cell size and organelles
Surface Area formula for cube (6s2)
Volume formula for a cube (s3)
Osmosis
Diffusion
Isotonic
Hypertonic
Hypotonic
Selectively Permeable Membrane
STATE/NATIONAL STANDARDS
Science
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Course - Biology
Course Content – Cells
Cell Structure and Function
Structure, function and interrelatedness of cell organelles
Eukaryotic cells and Prokaryotic cells
Cellular Processes
Characteristics of life regulated by cellular processes
Photosynthesis, chemosynthesis, cellular respiration
Cell division and differentiation
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Content Elaboration - Building on knowledge from middle school (cell theory), this topic focuses on the cells as
a system itself (singled-celled organism) and as part of a larger system (multicellular organism), sometimes as
part of a multicellular organism, and always as part of an ecosystem. The cell is a system that conducts a variety
of functions associated with life. Details of the cellular processes such as photosynthesis, chemosynthesis,
cellular respiration, cell division, and differentiation are studied at this grade level. Additionally, cellular
organelles studied are cytoskeleton, Golgi complex, and endoplasmic reticulum.
Every cell is covered by a membrane that controls what can enter and leave the cell. In all but quite primitive
cells, a complex network of proteins provides organization and shape. Within the cell are specialized parts for
the transport of materials, energy transformation, protein building, waste disposal, information feedback, and
movement. In addition to these basic cellular functions, most cells in multicellular organisms perform some
specific functions that others do not.
A living cell is composed of a small number of elements, mainly carbon, hydrogen, nitrogen, oxygen,
phosphorous and sulfur. Carbon, because of its small size and four available bonding electrons, can join to other
carbon atoms in chains and rings to form large and complex molecules. The essential functions of cells involve
chemical reactions that involve water and carbohydrates, proteins, lipids, and nucleic acids. A special group of
proteins, enzymes, enables chemical reactions to occur within living systems.
Cell functions are regulated. Complex interactions among the different kinds of molecules in the cell cause
distinct cycles of activities, such as growth and division. Most cells function within a narrow range of
temperature and pH. At very low temperatures, reaction rates are slow. High temperatures and/or extremes of
pH can irreversibly change the structure of most protein molecules. Even small changes in pH can alter how
molecules interact.
DAY 1 – CELL SIZE ACTIVITY
MATERIALS
Day One (per pair of students)
Xeroxed copies of cubic cell models on heavy paper, scissors, tape, sand, electronic balance
INSTRUCTIONAL PLAN ( STUDENT SHEETS SEPARATE FROM THIS DOCUMENT.)
A. INTRODUCTION
I will introduce the lesson by asking the students if the cells from a mouse are the same size of the cells from an
elephant. This will hopefully lead to a discussion as to whether the elephant is larger due to its cells being larger, or
if there are just more cells in an elephant body. We will discuss as a group that all cells are microscopic, and are
triggered to divide in half when the cell reaches a maximum growth/size or it will die. The students will build various
models representing cells of different sizes/stages of growth, and calculate the surface area and volume of each, and
the weight when the model is filled with sand. Students will then compare surface area-to-volume ratio, and surface
area-to-weight ratio.
B. ACTIVITY
Working in pairs, the students will cut out, fold, and tape the copies of the cube cell models, leaving the top
edge open so the model can be filled with sand. The models represent cells at increasing stages of growth – the
one cubic centimeter is the youngest, the 4 cubic centimeters is the largest. Calculate your measurements and
data, and fill in the following data table. (Answers in bold)
Using the materials provided, you and your partner will build models representing a cell in various stages of
growth, and compare the relationships between cell sizes, mass, surface area, and volume.
Cell Size in
cubic
centimeters
Total
Surface
Area
Volume of
Cube
1
2
3
4
6
24
54
96
1
8
27
64
Weight of
Cube filled
with Sand
in grams
Total
surface
area-tovolume
Ratio
6:1
3:1
2:1
3:2
Total
Surface
Area-toWeight
Ratio
Analysis questions (Answers in bold inside parenthesis)
1. Anything a cell takes in, like food or oxygen, or anything a cell must release, like wastes, must diffuse
through the cell membrane. Which of your data table columns best represents how much cell membrane a
cell has? (total surface area)
2. The cell contents, such as the cytoplasm and organelles, use the food and oxygen while producing the
wastes. Which of your data table columns best represents how much cytoplasm the cell has inside the
membrane? (volume)
3. As the cell grows larger, what happens to the total surface area-to-volume ratio? (decreases)
4. As the cell gains more mass, what happens to the total surface area-to-weight ratio? (decreases)
5. Why can’t cells survive when the total surface area-to-volume becomes too small? (bigger cells need more
stuff to survive, but have less surface to absorb/release with)
6. Which of these cell models has the best chance of survival? (smallest)
7. What could the largest cell do to increase its chance for survival, in other words, increase its total surface
area-to volume ratio? (split in half or divide)
C. POST ACTIVITY DISCUSSION
After the students have had time to construct and measure/mass the models, we will come together to discuss the
results and determine if they answered the questions correctly.
EXTENSIONS
Day 1 – Show students a video clip of the movie “The Blob” and discuss if this could be possible.
www.youtube.com/watch?v=nqZ86pJkz-M
ASSESSMENT
DAY 1
Student success will be determined during the post activity discussion – determining if the students
were able to answer the questions in regards to surface area and volume correctly. We will discuss the results,
determine the relationships between mass, total surface area, and volume. We will discuss how cells can only
grow so large before it must divide, or the cell will “starve” or “poison” itself.
.
REFERENCES
DAY 1
Ohio Department of Education Biology Syllabus and Curriculum Model
Modeling Limits to Cell Size, by James Deaver (www.accessexcellence.org/AE/AEC/AEF/1996/deaver_cell.php)
SAFETY CONSIDERATIONS
Day1 - Caution while using sharp instruments such as scissors, knives
DAY 2 – Osmosis and Diffusion Lab
MATERIALS – Day 2 (per pair of students)
Dialysis tubing, 200 ml beaker of distilled water, 15% glucose solution & 1% starch solution mixed together, 4 glucose
Testape strips, Lugols’s solution, string to tie the tubing/bag, gloves
INSTRUCTIONAL PLAN (STUDENT SHEETS SEPARATE FROM THIS DOCUMENT)
A. INTRODUCTION
In this activity, students will observe and determine if the diffusion of molecules has occurred through dialysis tubing,
which is an example of a selectively permeable membrane. Small molecules can move freely through the membrane, but
larger molecules may or may not move. The movement of the molecules through the membrane is determined by the
size of the pores in the membrane. From this activity, students will determine which molecules have passed through the
membrane and which did not, and determine the relative size of the molecules by comparing the ability to pass through
the membrane.
B. ACTIVITY
Working in pairs, the students will obtain a piece of 6 inch dialysis tubing that has been soaking in water to soften. Tie
one end of the tubing in a knot to seal it shut. Pour approximately 15 ml of the sugar/starch solution into the bag.
Before tying the top of the bag shut, use a glucose Testape to verify the presence of sugar in the bag. Use a second
glucose Testape to test the beaker of distilled water to prove the lack of glucose in the water. Add 4 mls of Lugol’s
indicator solution to the beaker of water. Record the color. Tie the bag shut, and soak the dialysis bag in the beaker of
distilled water for 30 minutes. Remove the bag and record the color of both the beaker and the bag. Using glucose
Testape strips, test for the presence of glucose in both the bag and the beaker. Fill in your data table, and answer the
following questions. (Answers in bold)
Bag
Beaker
Initial
Contents
Glucose & Starch
Water & Lugol’s
Solution Color
Initial
clear
gold
Final
Black/blue
gold
Presence of Glucose
Initial
Final
yes
yes
no
yes
Analysis Questions (Answers in bold)
1. Which substance(s) are leaving the bag, and which are entering the bag? What evidence do you have to support
these results? Glucose leaves the bag, Lugol’s enters the bag. The color change and the Testape strips
provide the evidence.
2. Explain the results you observed – include concentration differences and membrane pore size in your answer.
Both glucose and Lugol’s molecules move from high to low concentrations. The membrane pores are large
enough to let glucose, water, and Lugol’s through, but not starch molecules.
3. How could you modify this experiment to show quantitative data supporting the rationale that water diffused
from the beaker into the dialysis tubing? Weigh the bag both before and after on an electronic balance
4. Based on your observations, rank the following molecules by relative size, from smallest to largest – glucose,
water, Lugols’s (IKI), starch membrane pores. IKI, water, glucose, pores, starch
5. What results would you expect if the lab started with a glucose and Lugol’s solution in the bag, and starch and
water in the beaker? Why? The beaker would turn dark as the Lugol’s moved out of the bag into the beaker
where the starch is, glucose would move out of the bag into the beaker, and water would move from the
beaker into the bag. All movement is down the concentration gradient by diffusion/osmosis. The bag does
not change color because starch cannot enter the bag due to pore size being smaller than the molecule.
C. POST ACTIVITY DISCUSSION
After the students have completed the lab activity, we will come together as a class and discuss the direction of
movement of the molecules. The students will explain how the results showed the movement of molecules from areas
of high concentration to areas of low concentration through a selectively permeable membrane.
EXTENSIONS
Day 2 – Have students explain why getting tears in your eyes burns; why IV solutions are saline solutions instead of just
water; how perfumes and colognes “work”, etc.
ASSESSMENT
Day 2 - Student success will be determined during the post activity discussion – determining if the students were able to
answer the questions in regards to diffusion, osmosis, and selectively permeable membranes.
REFERENCES
Day 2 – 2002 The College Board, College Board, Advanced Placement Program, Biology Lab One Diffusion and Osmosis
(www.collegeboard.org)
SAFETY CONSIDERATIONS
Day 2 – Lugol’s Indicator Solution will stain skin and clothes, students should wear gloves and use caution while handling
Lugol’s. Use caution while working with glassware.
Day 3 – French Fries and Sugar Water Lab
MATERIALS – (per pair of students)
Day 3 – Raw Potatoes, Mandolin or French Fry cutter, electronic balances, metric rulers, cups or beakers, sugar, distilled
water, paper towel
INSTRUCTIONAL PLAN
A. INTRODUCTION
In this activity, students will apply the knowledge they have gained from the previous activities. The students will have to
create solutions of different concentrations – one that will make the potato French fry gain mass, one that will make the
potato lose mass, and one that will stay relatively unchanged.
B. ACTIVITY
Working in pairs, with the materials provided, the students will design an experiment to determine the concentrations of
sugar solutions that will cause the potato French fry to gain mass, to lose mass, and to remain the same mass. The
concentrations of sugar solutions should range from between 0.01% and 10%. The potato French fries should be of the
same size, and dimensions. The French fries should remain soaking in the solutions for equal amounts of time, 30
minutes, if time allows.
C. POST ACTIVITY DISCUSSION
After the students have completed the lab, we will come together as a class to discuss the results. The discussion should
include determining which solution(s) were most hypertonic and made the French fries lose mass, which solution(s) were
more hypotonic and made the French fries gain mass, and which solution(s) were more isotonic and the French fries
remains the same mass.
EXTENSIONS
Have the students write a paragraph explaining when the potatoes are growing in the ground, do they swell with water
when it rains? If not, explain why they don’t, and is this an advantage or disadvantage?
ASSESSMENT
Day 3 – Student success will be determined with analyzing questions, and the accuracy of the answers. (Answers in bold)
1. Why are cells small, and why do they have cell membranes with many convolutions?
Small due to surface area/volume restrictions. Convolutions to increase surface area
2. Do you believe osmosis occurs when a cell is in an isotonic solution? Explain your reasoning.
Yes, diffusion/molecule movement is random and constant until equilibrium is reached
3. What cell organelle(s) is needed to keep a cell from gaining so much mass in a hypotonic solution the cell would
actually burst or lyses? Contractile vacuole, cell wall, etc
REFERENCES
Day 3 - 2012The College Board, College Board, Advanced Placement Program, Biology Lab, Big Idea 2: Cellular Processes,
(Diffusion and Osmosis) www.collegeboard.org
SAFETY CONSIDERATIONS
DAY 3 – Use caution when using sharp instruments such as French fry cutter or mandolin
DAY 1 STUDENT SHEET– GRID SHEET TO CUT OUT FOR CELL SIZE ACTIVITY
DAY 1 STUDENT SHEET
A. ACTIVITY
Working in pairs, cut out, fold, and tape the copies of the cube cell models, leaving the top edge open so the
model can be filled with sand. The models represent cells at increasing stages of growth – the one cubic
centimeter is the youngest, the 4 cubic centimeters is the largest. Calculate your measurements and data, and
fill in the following data table.
Using the materials provided, you and your partner will build models representing a cell in various stages of
growth, and compare the relationships between cell sizes, mass, surface area, and volume.
Cell Size in
cubic
centimeters
Total
Surface
Area
Volume of
Cube
Weight of
Cube filled
with Sand
in grams
Total
surface
area-tovolume
Ratio
Total
Surface
Area-toWeight
Ratio
1
2
3
4
Analysis questions
1. Anything a cell takes in, like food or oxygen, or anything a cell must release, like wastes, must diffuse
through the cell membrane. Which of your data table columns best represents how much cell membrane a
cell has?
2. The cell contents, such as the cytoplasm and organelles, use the food and oxygen while producing the
wastes. Which of your data table columns best represents how much cytoplasm the cell has inside the
membrane?
3. As the cell grows larger, what happens to the total surface area-to-volume ratio?
4. As the cell gains more mass, what happens to the total surface area-to-weight ratio?
5. Why can’t cells survive when the total surface area-to-volume becomes too small?
6. Which of these cell models has the best chance of survival?
7. What could the largest cell do to increase its chance for survival, in other words, increase its total surface
area-to volume ratio?
DAY 2 – STUDENT SHEET
In this activity, students will observe and determine if the diffusion of molecules has occurred through dialysis tubing,
which is an example of a selectively permeable membrane. Small molecules can move freely through the membrane, but
larger molecules may or may not move. The movement of the molecules through the membrane is determined by the
size of the pores in the membrane. From this activity, students will determine which molecules have passed through the
membrane and which did not, and determine the relative size of the molecules by comparing the ability to pass through
the membrane.
A. ACTIVITY
Working in pairs, the students will obtain a piece of 6 inch dialysis tubing that has been soaking in water to soften. Tie
one end of the tubing in a knot to seal it shut. Pour approximately 15 ml of the sugar/starch solution into the bag.
Before tying the top of the bag shut, use a glucose Testape to verify the presence of sugar in the bag. Use a second
glucose Testape to test the beaker of distilled water to prove the lack of glucose in the water. Add 4 mls of Lugol’s
indicator solution to the beaker of water. Record the color. Tie the bag shut, and soak the dialysis bag in the beaker of
distilled water for 30 minutes. Remove the bag and record the color of both the beaker and the bag. Using glucose
Testape strips, test for the presence of glucose in both the bag and the beaker. Fill in your data table, and answer the
following questions.
Bag
Beaker
Initial
Contents
Glucose & Starch
Water & Lugol’s
Solution Color
Initial
Final
Presence of Glucose
Initial
Final
Analysis Questions
1. Which substance(s) are leaving the bag, and which are entering the bag? What evidence do you have to support
these results?
2. Explain the results you observed – include concentration differences and membrane pore size in your answer.
3. How could you modify this experiment to show quantitative data supporting the rationale that water diffused
from the beaker into the dialysis tubing?
4. Based on your observations, rank the following molecules by relative size, from smallest to largest – glucose,
water, Lugols’s (IKI), starch membrane pores.
5. What results would you expect if the lab started with a glucose and Lugol’s solution in the bag, and starch and
water in the beaker? Why?
DAY 3 STUDENT SHEET
In this activity, students will apply the knowledge they have gained from the previous activities. The students will have to
create solutions of different concentrations – one that will make the potato French fry gain mass, one that will make the
potato lose mass, and one that will stay relatively unchanged.
A. ACTIVITY
Working in pairs, with the materials provided, the students will design an experiment to determine the concentrations of
sugar solutions that will cause the potato French fry to gain mass, to lose mass, and to remain the same mass. The
concentrations of sugar solutions should range from between 0.01% and 10%. The potato French fries should be of the
same size, and dimensions. The French fries should remain soaking in the solutions for equal amounts of time, 30
minutes, if time allows.
B. POST ACTIVITY DISCUSSION
After the students have completed the lab, we will come together as a class to discuss the results. The discussion should
include determining which solution(s) were most hypertonic and made the French fries lose mass, which solution(s) were
more hypotonic and made the French fries gain mass, and which solution(s) were more isotonic and the French fries
remains the same mass.
EXTENSIONS
Have the students write a paragraph explaining when the potatoes are growing in the ground, do they swell with water
when it rains? If not, explain why they don’t, and is this an advantage or disadvantage?
ASSESSMENT
1. Why are cells small, and why do they have cell membranes with many convolutions?
2. Do you believe osmosis occurs when a cell is in an isotonic solution? Explain your reasoning.
3. What cell organelle(s) is needed to keep a cell from gaining so much mass in a hypotonic solution the cell would
actually burst or lyses?