Plasma Membrane Model


Build an engaging model to bring the fluid mosaic theory of membrane structure out of the textbook and into the classroom. The model is a great teaching aid to illustrate the properties of the plasma membrane structure, such as its function, fluidity and membrane-bound proteins.


  • Fluid mosaic model

  • Membrane proteins
  • Plasma membrane
  • Selective permeability


The fluid mosaic model is the scientifically accepted theory for the structure of cellular membranes (also referred to as plasma membranes). Every living cell, from simple bacteria to complex plant and animal cells, contain a lipid bilayer membrane. Cell membranes, along with the cytoskeleton, holds a cell’s shape and keeps cytoplasm from leaking into the extracellular matrix. The membrane is selectively permeable—it functions as a gatekeeper, monitoring and facilitating the entry and exit of molecules into and out of the cell.

{10703_Background_Figure_1_Schematic of bilayer membrane}

The membrane is best described as fluid in nature, hence the name of the structure model, fluid mosaic. Phospholipid molecules move freely throughout the membrane while the structure of the membrane remains unchanged. The molecular structure of the membrane plays an important role in functionality of the membrane. Plasma membranes are composed of a bilayer of phospholipids, with interspersed protein molecules (see Figure 1). Each phospholipid has two distinct parts, a polar, hydrophilic (water loving) head and two non-polar, hydrophobic (water hating) tails. The hydrophobic tails form the inferior core of the membrane—they point away from both the watery extracellular matrix and the aqueous cytosol within the cell. The hydrophilic heads line up on the inside and outside surfaces of the cell, creating the bilayer membrane (see Figure 2).

{10703_Background_Figure_2_Schematic of phospholipid molecule—a membrane building block}

Membrane proteins play several important roles in the function of a cell. Imagine membrane proteins as being similar to icebergs in the ocean. They tend to stay in the same general location but may drift. Some proteins span the entire length of the membrane, whereas others are located mainly on the surface of the membrane. Most membrane-bound proteins act as ion channels or pumps actively moving wastes out of the cell and moving necessary ions (e.g., potassium, calcium) into the cell. Certain membrane-bound proteins, called receptors, attach to horomones and other molecules on the outer side of the membrane and pass information to the inside of the cell without allowing the molecule to enter. Several types of membrane-bound proteins may be shown using this model.


Glycerin, 150 mL*
Mineral oil, 500 mL*
Gorilla Glue®, 1 mL
Magnetic stirring bar*
Phospholipids, plastic, bottom layer, 14*
Phospholipids, Styrofoam®, top layer, 14*
Pipet, wide-stem*
Plastic canister*
Stoppers, cork, 2*
*Materials included in kit.

Safety Precautions

Wear chemical splash goggles and chemical-resistant gloves while setting up the model initially. Encourage students to follow all normal laboratory procedures. Do not allow students to open the lid of the model, as this may result in spillage of the contents.


Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Store the model for future use. If necessary, solutions may be disposed according to Flinn Suggested Disposal Method #26b.

Prelab Preparation

  1. Add 150 mL of glycerin to the plastic canister.
  2. Add 500 mL of mineral oil to the plastic canister.
  3. Add the 14 plastic bead phospholipids to the canister. The beads will sink slowly, forming the bottom layer of the membrane. The “tails” may need to be gently tapped with a pipet forcing air bubbles out causing them to sink.
  1. The tails of the top phospholipid layer will need to be filled with mineral oil in order for them to sit properly in the model. Hold a phospholipid upside down over the open canister. Slowly drip mineral oil into the tail using the wide-stem pipet until both sides are completely full. To prevent oil from spilling out of the tail, quickly flip the phospholipid over while placing it into the canister. Repeat for each remaining phospholipids. These balls will float, forming the top layer of the membrane.
  2. To assemble the membrane protein, insert the two corks into the V-shaped arms of the Y-connector. This will be the top of the protein (see Figure 3).
  3. Place Gorilla Glue around the half of the magnet which will be inserted into the Y-shaped tube. Insert the glued half of the magnetic stirring bar into the base of the Y-shaped plastic tube, until the pivot ring in the center is reached. Half of the stir bar will extend out from the tube. Allow at least three hours for Gorilla Glue to set.


  1. Observe and identify the parts of the membrane. Note: Some observant students may notice that the hydrophobic heads have a different appearance in the top and bottom layers of the model. Explain that they are composed of the same molecular structure in an actual cell.
  2. To show the fluidity of the cellular membrane, simply rock the model or allow students to do so, showing how individual phospholipids move in a fluid motion, yet the overall structure remains unchanged.
  3. Add the “membrane protein” to the model, magnet side down. Using a strong magnet on the sides or the bottom of the canister, move the protein structure to represent how protein receptors can move through the membrane as the phospholipids do without disrupting the structure of the membrane.
  4. Depending on the level of the class, the protein structure in this model can represent several different types of membrane proteins and glycoproteins, such as receptors, channels, integral proteins, oligosaccharides and other membrane-bound carbohydrates. Move the protein to different locations within the membrane using a magnet on the outside of the canister to achieve models of the different membrane structures.
  5. Creative representations for the corks and the stirring bar are possible as well. For example, if you would like to use the protein to represent a receptor, the corks could represent ligands such as hormones. To show a channel, position the protein so that it spans the thickness of the membrane. The magnetic stir bar may represent a molecule moving across a concentration gradient from the inside to the outside of the cell.

Student Worksheet PDF


Teacher Tips

  • Use this model as a teaching tool when discussing topics associated with the cellular membrane, such as plasma membrane structure and function, diffusion, active and passive transport, selective permeability, osmosis, endocytosis and exocytosis.

  • Any strong magnet, including cow, mega and neodymium, will work to move the “protein” into different positions in the membrane model.
  • If you wish to break down the model at the end of the school year, glycerin and mineral oil may be purchased from Flinn Scientific, Inc. (Catalog Nos. G0007 and M0064, respectively).

Correlation to Next Generation Science Standards (NGSS)

Science & Engineering Practices

Developing and using models

Disciplinary Core Ideas

MS-LS1.A: Structure and Function
HS-LS1.A: Structure and Function

Crosscutting Concepts

Structure and function

Performance Expectations

MS-LS1-6: Construct a scientific explanation based on evidence for the role of photosynthesis in the cycling of matter and flow of energy into and out of organisms.
HS-LS1-5: Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy.
HS-LS2-4: Use mathematical representations to support claims for the cycling of matter and flow of energy among organisms in an ecosystem.

Answers to Questions

  1. Why is the plasma membrane considered to be fluid in nature?

    Phospholipid molecules move freely throughout the membrane in a fluid motion, while the overall structure of the membrane remains unchanged.

  2. Describe the structure and orientation of phospholipids in the plasma membrane. What properties of the membrane impact the physical structure?

    Each phospholipid has two distinct parts, a polar, hydrophilic head and two non-polar, hydrophobic tails. The hydrophobic tails arrange in orientation forming the interior core of the membrane, whereas the heads form the inside and outside surfaces of the membrane.

  3. What does it mean to say that the membrane is selectively permeable rather than totally permeable?

    Selective permeability refers to the fact that the membrane functions as a gatekeeper, monitoring and facilitating the entry and exit of molecules into and out of the cell.

  4. List some of the functions of membrane proteins.

    Many membrane-bound proteins act as ion channels or pumps actively moving wastes out of the cell and moving necessary ions (e.g., potassium, calcium) into the cell. Certain membrane-bound proteins function as receptors relaying messages into the cell.

  5. Sketch the general structure of the plasma membrane and label the parts.

    Accept any reasonable drawings.

Next Generation Science Standards and NGSS are registered trademarks of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.