By: Kasia Hirniak
SBI4U Biochemistry: Cellular Transport Concept Presentation
Overall Curriculum Expectation:
B2. investigate the chemical structures, functions, and chemical properties of biological molecules involved in
some common cellular processes and biochemical reactions
Specific Curriculum Expectations:
B2.2 plan and conduct an investigation to demonstrate the movement of substances across a membrane (e.g., the
effects of salt water and distilled water on a potato).
B3.6 describe the structure of cell membranes according to the fluid mosaic model, and explain the dynamics of
passive transport, facilitated diffusion, and the movement of large particles across the cell membrane by the
processes of endocytosis and exocytosis.
Background Information:
Our current model of the cell membrane is called the fluid mosaic model. The membrane contains proteins that
have a variety of functions. For example, some proteins are receptors which can detect the presence of certain
kinds of molecules in the surrounding environment. It is a lipid bilayer, meaning it is made of two layers of
fatty molecules (called phospholipids) sandwiched together. Phospholipids have a hydrophilic (or polar) head
and two long, hydrophobic (or nonpolar) tails. Molecules like this are called amphipathic.
The primary function of a cell membrane is to control the passage of materials into and out of the cell.
Membranes contain other molecules such as proteins which may function as channels for moving materials into
and out of the cell, markers used for cell recognition, receptors for hormones, pumps for transporting materials
across the membrane. Glycoproteins are proteins with sugars attached. They function in cell recognition.
The cell membrane prevents equal motion of water and dissolved substances from inside to outside of the cell.
Many substances cannot pass through biological membranes. The transport of materials across a cell membrane
falls into two general categories. The first is passive transport which does not require energy use by the cell and
includes diffusion, osmosis and facilitated diffusion. All molecules move continuously by random simple
diffusion. Diffusion is the movement of particles from an area of higher concentration to an area of lower
concentration. When water diffuses across a selectively permeable membrane, it is called osmosis. It occurs
when a solute cannot pass through a membrane but the solvent (water) can. Water moves from an area where
there is more water to an area where there is less water. In general, water moves toward the area with a higher
solute concentration because it has a lower water concentration. Some important molecules, like glucose, are
helped across the cell membrane so that they move into a cell faster. Special protein channels help move these
substances across the membrane through a process called facilitated diffusion.
The 3 types of solutions include Hypotonic, a solution which is more dilute (i.e., less solutes) than the cytosol.
The cell gains water and swells. Hypertonic, a solution which is more concentrated (i.e., more solutes) than the
cytosol. The cell loses water and shrinks. And Isotonic, a solution which has the same concentration of solutes
as the cytosol. The cell neither gains nor loses water and remain unchanged. Osmotic swelling dilutes the
cytosol and can eventually cause the cell to burst (lyse). The opposite problem, the cell shrinking, would occur
in a hypertonic solution.
The second category is active transport. When a cell requires substances that are at a lower concentration
outside the cell than inside the cell, these substances will not move by the means of diffusion but instead by
active transport. Special proteins in the membrane use energy to transport these substances into the cell.
Examples include endocytosis, phagocytosis and pinocytosis. These processes are used for macromolecules
that are too big to pass through the cell membrane normally. Phagocytosis is bringing particles into the cell
By: Kasia Hirniak
while pinocytosis is bringing in fluid. Exocytosis is the opposite wherein the materials are excreted from a cell
but the mechanism is the same.
http://www.youtube.com/watch?v=4c1r8ydVuds
 provides a summary of the above background knowledge in a 9minute video
Advance Preparation/Student Prior Knowledge:
Students should have a good understanding of the following concepts:
 Cell structure and function
 Molecules are always in motion
 Cell permeability
 Cells store and use energy for building materials, transport and controlling life processes
 Cells need chemical compounds to perform functions and build structures
 The law of diffusion
Special Materials:
 Computer, LCD projector
 metal paper fasteners (5 sets of 20)
 cotton swabs
 drinking straws
 pipe cleaners
Student Difficulties:
Student Difficulty
Rectification
Students may have difficulty learning to think about
the processes at the molecular level.
Students may believe that in diffusion when the
molecules are evenly spread out they stop moving.
Showing students animations and videos can help
them visualize how the processes work.
Students may confuse osmosis and diffusion by
thinking they are the same.
Students may confuse diffusion with dissolving.
Students may find the concept of tonicity (isotonic,
hypotonic, hypertonic) difficult to understand. They
may have hard time remembering which direction
water moves in each of the three types of solutions.
Engaging students in a lab or showing them a
demonstration can help them differentiate between
different processes.
Suggested Demonstrations/Labs and Additional Annotated Internet Addresses/References:
The following demonstrations may be shown to students to illustrate osmosis.
Elodea Demonstration: Place Elodea leaves on two microscope slides. Add a drop of distilled water to one, and
a drop of salt water to the other. After about 5 minutes, observe each leaf under a microscope. Students will see
that cells in the saltwater solution have undergone plasmolysis, a process in which the cell membrane pulls back
from the cell wall.
By: Kasia Hirniak
Grape Demonstration: Place grapes in containers of distilled water, grape juice, and corn syrup. Let them sit
overnight. Measure the mass of each grape the next day. Like the egg, the grapes in corn syrup will be smallest
because of water loss from osmosis.
Salty Potatoes Demonstration: Cut a potato in half, and then use a spoon to scoop a depression into the round
end of each half. Add a pinch of salt to one depression, and leave the other alone. After about five minutes, the
salty depression will fill with water while the other depression will be dry. Osmosis pulls water from the potato
cells into the salty solution.
http://www.biotopics.co.uk/life/osmsis.html
 includes a review of diffusion, two demonstrations of osmosis one using Visking tubing and the second
using a potato tissue with accompanying questions.
Egg Demonstration: Place a raw egg in vinegar and let it sit overnight to dissolve the shell. Place the egg in
distilled water one day and find its mass and circumference. Then, place the egg in corn syrup, let it sit
overnight, and measure it again. Students will see that the egg expands in size when placed in distilled water
and shrinks in size when placed in corn syrup.
http://staff.tuhsd.k12.az.us/gfoster/standard/labosmosis.htm
 a lab allowing students to experiment with the process of osmosis in hypertonic, hypotonic and isotonic
solutions using an egg.
http://www.youtube.com/watch?v=0c8acUE9Itw
 a 4min long video showing the process of osmosis using an egg. Students are able to see the egg reduce in
size when submerged in corn syrup and grow in size as the egg is placed in freshwater.
http://www.youtube.com/watch?v=ULR79TiUj80
 a short (1min:27secs) Fluid Mosiac Model video discusses the structure of the cell membrane, its
components and their function.
http://www.explorelearning.com/index.cfm?method=cResource.dspDetail&ResourceID=418
 Osmosis Gizmo allows students to investigate how solute concentrations affect the volume of a cell and how
changing the cell volume affects solute concentrations.
http://science-class.net
 provides resources for elementary and middle school science teachers, lessons/slideshows, labs,
simulations/videos, student worksheets/handouts, quizzes, study notes, review games etc
http://home.earthlink.net/~shalpine/anim/Life/memb.htm
 an interactive demonstration of the structure and function of the cell membrane.
http://www.johnkyrk.com/diffusion.html
 a simple animation showing a high concentration of molecules in the center of the page. As you watch, they
will diffuse through random molecular motion.
http://www.wisc-online.com/objects/index_tj.asp?objid=AP11003
 a tutorial that will help understand the process of osmosis.
http://www.wisc-online.com/objects/index_tj.asp?objid=AP11203
a learning activity showing endocytosis, exocytosis, and active transport.
By: Kasia Hirniak
http://www.youtube.com/watch?NR=1&v=Kd3LorZcJew
 video showing the sodium/potassium pump as an example of active transport
Applications and Societal issues:
 The effect of Marathon runners drinking fluids that contain sugar and salt.
 The reason for gardeners to soak fresh vegetables from the garden in saltwater before rinsing them and
soaking them in freshwater.
 The rationale behind grocery stores spraying their vegetables with water to preserve their freshness.
 Osmosis being vital to many body processes, including: blood filtration by the kidneys and the workings
of the nerves.
 The importance of diffusion in cellular respiration, wherein cells take in oxygen and push out waste
carbon dioxide.
 Malfunction of the chlorine channel causes cystic fibrosis.
 The secretion of insulin from pancreatic cells into the blood by exocytosis to lower blood sugar level
preventing diabetes.
 Build-up of cholesterol in cell membranes leading to atherosclerosis.
Teaching Ideas:
Several instructional strategies can be used to teach the concept of Cellular Transport. I suggest introducing the
topic by assessing what students already know about cell membranes and cellular transport. This can be
achieved using a KWL chart. The L section of the KWL chart should be completed on the last day and can be
used as a diagnostic before test preparation.
Using graphic organizers and video simulations/Gizmo to differentiate the active and passive transports will
appeal to visual learners while using strategies that allow students to work in groups such as the classroom
stations and the introductory activity of building the model of the cell membrane, will appeal to interpersonal
and verbal learners. All students will benefit from the inquiry oriented hands-on osmosis lab activity. Acting as
a classroom facilitator the teacher should clearly explain both the procedure and the expectations prior to the
start of the lab as to ensure proper lab technique and safety. This review should include the proper handling of
all laboratory equipment, proper dress code, potential hazards and steps to follow in case of a lab accident.
Kinesthetic learners will appreciate the opportunity to get out of their seats for the classroom stations activity. In
order to minimize classroom management issues, students should be assigned with specific roles within the
group such as the note taker, the time watcher etc. Each station should also be provided with a labeled diagram
of how each station should look like when it comes to clean up time to ensure an organized end to the activity.
Assessment Strategies:
Assessment for Learning:
 Cellular Transport KWL chart
 Cell Membrane/Cellular Transport Diagnostic Quiz
 Cell Membrane/Cellular Transport Concept Map
 Introductory Cooperative group Activity (building a model of the cell membrane)
By: Kasia Hirniak
Assessment as Learning:
 Journal Entry (K/U, C)
 Gizmo activity worksheets (K/U)
 Osmosis Lab worksheets (K/U, A, T/I)
 Classroom stations worksheets (K/U, T/I)
 PowerPoint reflection Think-Pair-Share activity (K/U)
 List of substances and their mode of transport homework question (K/U, T/I)
Assessment of Learning:
 Osmosis Lab report (C, T/I)
 Classroom Stations Peer/Self evaluation (C, A)
 Cell Membrane and Cellular Transport Quiz (K/U, A)
Suggested Lesson Sequence:
1. Lesson Goal: The structure and composition of the cell membrane
Diagnostic Cooperative group Activity
- arrange class into groups,
- provide each group with 20 metal paper fasteners
- tell students to assume that each metal paper fastener is a phospholipid and ask them to come up with all
possible arrangements that the 20 phospholipids would form in the presence of water
- lead the class to realization that a cell membrane forms a phospholipid bilayer structure
Show students a PowerPoint presentation covering:
- review of lipids and key properties
- basic structure of the phospholipid molecule, hydrophobic tails and hydrophilic heads
- structure of a cell membrane
- components of cell membrane: phospholipids, protein channels, glycoproteins, cholesterol etc
- assess understanding through a Think-Pair-Share Activity
- show students the following video:
Fluid Mosiac Model Video
http://www.youtube.com/watch?v=ULR79TiUj80
Assessment: Ask students to write a journal entry addressed to an absent student explaining the structure and
composition of the cell membrane, ensuring to provide a labeled diagram of the cell membrane.
2. Lesson Goal: Passive transport: diffusion, facilitated diffusion, osmosis and Active transport: endocytosis,
exocytosis
Introduce the concept of Diffusion and Osmosis by performing the Salty Potatoes Demonstration, ask students
to predict what will happen, and then ask them to explain the results.
Students complete the Osmosis Gizmo
http://www.explorelearning.com/index.cfm?method=cResource.dspDetail&ResourceID=418 Or
The following Egg Osmosis Lab
http://staff.tuhsd.k12.az.us/gfoster/standard/labosmosis.htm
After the students are finished with either one of the above activities, introduce Active transport by
differentiating it from the passive transport (passive transport involves the movement of substances down their
By: Kasia Hirniak
concentration gradient and the active transport moves substances against their concentration gradient; passive
transport does not require ATP and active transport requires ATP).
Show students the following video on active transport:
http://www.youtube.com/watch?NR=1&v=Kd3LorZcJew
Have a class discussion reflecting on the video and ensuring student understanding
Assessment: Ask students to make a list of substances with their mode of transport across cell membranes.
Assessment: Gizmo Worksheets or Lab Report
3. Lesson Goal: Cellular Transport Stations
Students will rotate around 4 stations set up around the classroom completing activities provided below.
Station 1: Build a Model of the Cell Membrane
Use the following materials to build a model of the cell membrane. Explain what each material represents:
1. Cotton Swabs: ______________________________________________
2. Pipe Cleaners: ______________________________________________
3. Drinking Straw: _____________________________________________
Station 2: Label with a number and explain the given structures
1.Phosopholipids 2.Glycoprotein 3.Cholesterol
4.Hydrophobic fatty acids 5.Protein channels
By: Kasia Hirniak
Station 3: Identify the type of Cell Transport
By: Kasia Hirniak
Station 4: Explain how each of the following travels across the cell membrane
1. Glucose: ___________________________________________________
2. Virus: __________________________________________
3. Na+ ion: _____________________________________________________
4. Pepsin: ___________________________________________________
5. Neurotransmitters: _____________________________________________
6. Oxygen: ____________________________________________________
Assessment: Peer and Self-Evaluation, Quiz