Download Name: Per. _____ Date: Cell Membrane Structure and Function

Name: ________________________________________________ Per. _____ Date: __________________________
Cell Membrane Structure and Function: Lego Modeling Activity
Have 1 group member read the passage below out loud. Discuss the brainstorm questions with your table group.
After you discuss, write your responses. Which group member is the reader? ____________________
Cells are found in all different types of environments, and these environments are constantly changing. One-celled
organisms, like bacteria, can be found on your skin, or in the ground, or in all different types of water. The cells of
your body interact with the food you eat, and also with other cells in your body. All cells need a way to protect
themselves. This job is done by the cell membrane.
The cell membrane is semipermeable, or selectively permeable, which means that only some molecules can get
through the membrane. A cell must be able to take in the resources it needs in order to carry out the processes to
sustain life. It must also be able to rid itself of wastes. In addition, it must keep out other substances that are
harmful or otherwise not desired by the cell.
How can a cell membrane have selective permeability? How does the cell control what molecules enter and leave the
cell? The ways that cells control what passes through the cell membrane will be the focus of this lesson.
Brainstorming Questions (discuss with your table group and answer below):
Describe what you think might be important functions of the cell membrane.
What kinds of substances or molecules might be in the environment that the cell needs?
In what ways might a cell membrane be like skin? Does the skin let any substances in or out? How do you think the
skin might do this?
Task 1: The Phospholipid Bilayer
The cell membrane is made of different types of molecules. The primary type of molecule
is called a phospholipid. A phospholipid is a molecule made of phosphorus and oxygen
atoms attached to a glycerol molecule (head). This in turn is attached to two fatty acid
chains (tail). The head of the phospholipid is polar, and therefore attracted to water. The
tail is non-polar, and repels water. Since cells are surrounded by water and also contain
water, how could phospholipids arrange themselves into a flexible layer that would
separate the inside of the cell from its outside environment? Draw the phospholipid arrangement in the zoom-in.
The structure of the cell membrane is called a lipid bilayer. Why does this arrangement allow for molecules with one
hydrophobic end and one hydrophilic end to exist in an environment that has water on both sides?
How might substances be able to make their way through this membrane?
On your whiteboard, draw a section of a lipid bilayer. Draw your model so that small particles can pass through
spaces in between the phospholipids, but larger molecules cannot. The following things will represent your large
and small molecules:
Small and Skinny Legos = Oxygen, carbon dioxide, and water molecules
Square Legos = Sodium (Na) and Potassium (K)
All long Legos = Glucose or other monomers
Put a higher concentration of molecules outside of the cell than inside the cell. Show how the molecules would
move in this situation. Make corrections to your model if necessary.
Which group member demonstrated this task? ________________________________
What types of molecules are able to move by simple diffusion in this model?
Does the cell have to do any work (spend energy) for this diffusion to happen? Explain.
Task 2: Channel Proteins and Passive Transport
Small molecules tend to move unassisted across the lipid bilayer from a region of high concentration to a region of
low concentration, due to the random movement of molecules. In general, only very small molecules such as water,
oxygen, and carbon dioxide can move through a membrane by diffusion. Larger molecules like glucose get through
the membrane by facilitated diffusion, or passive transport. Just like in simple diffusion, molecules move down the
concentration gradient. However, the molecules pass through channels, or tunnels in the membrane. The channels
are made of proteins embedded in the lipid bilayer that extend all the way through the layer.
Modify the lipid bilayer on your whiteboard to include components that would allow glucose into and out of the
cell. Show what would happen if there was a higher concentration of glucose molecules inside the cell than
outside the cell.
Which group member demonstrated this task? __________________________________
What components of the cell membrane can allow for large molecules like glucose to move across the membrane?
Why is no energy required for this type of movement of molecules?
Why can’t amino acids and glucose move across the phospholipid bilayer through simple diffusion? (Why do they
need channel proteins?)
Task 3: Carrier Proteins and Active Transport
Sodium (Na+) and potassium (K+) are ions that move across cell membranes. To
prevent too much water diffusing into the cell due to osmosis, the cell needs to
get rid of Na+ ions, but there are already more Na+ ions outside of the cell than
inside the cell. And to carry out metabolic processes, cells need many, many
potassium ions, but cells already contain more K+ ions inside than outside the cell.
In other words, cells must move these molecules across the membrane from a
lower concentration to a higher concentration, UP the concentration gradient.
This movement requires energy and is called active transport. Structures called
carrier proteins enable active transport to happen. Specific substances (like potassium or sodium) can bond to the
surface of the carrier protein. When this happens, the protein changes shape and results in the bonded substance to
move across the membrane. See the figure for an example of how this happens.
Modify the membrane on your whiteboard by adding structures that will move particles like potassium and
sodium UP the concentration gradient. Show how these molecules would move across the membrane.
Which group member demonstrated this task? ____________________________________
Why would a cell use active transport instead of facilitated diffusion to move molecules in and out of the cell?
What is a disadvantage to active transport (compared to passive transport)?
Where might cells get the energy required for active transport?
Summary Table
Definition
Passive Transport
Simple
Diffusion
Facilitated
Diffusion
Active
Transport
Quick sketch
Why is this important for
cells?
Does this
require
energy?
Name: _________________________________________________ Per. ______ Date: _____________________
Cell Membrane Exit Ticket
What is the purpose of the cell membrane?
Draw a model of a cell membrane in the space below and label the following things: phospholipid, channel protein,
carrier protein.
Which of the following requires energy?
A. Simple diffusion
B. Passive transport
C. Active transport
Name: _________________________________________________ Per. ______ Date: _____________________
Cell Membrane Exit Ticket
What is the purpose of the cell membrane?
Draw a model of a cell membrane in the space below and label the following things: phospholipid, channel protein,
carrier protein.
Which of the following requires energy?
A. Simple diffusion
B. Passive transport
C. Active transport