Modeling the Cell Membrane - Father Son Innovations



Modeling the Cell Membrane Lab

Pre-lab Questions

1. List the molecules that make up the structure of the cell membrane.

2. What is the major difference between Active & Passive Transport?

Background:

The cell membrane is made up of a double layer of phospholipids, known as the lipid bilayer. Part of the phospholipid is hydrophilic (water-loving) and part is hydrophobic (water-repelling). This causes the phospholipids to be arranged in a very specific way with the hydrophobic tails facing inward (center) and the hydrophilic heads facing outwards. In this activity the Q-tips represent the phospholipids. However, one Q-tip equals two phospholipids (see figure 1).

[pic]

Fig. 1- Q-tip Phospholipid Model

The function of the cell membrane is to both separate the cell from what surrounds it and, most importantly, control (regulate) what is able to enter and exit the cell. The cell membrane is selectively permeable meaning that only certain things are able to enter and leave the cell easily. Think of the cell membrane as the exterior walls and roof of your home. It’s scattered with a number of windows, doors and vents. Just like the cell, these items help to control what enters and exits your home. Passive transport happens without the cell needing to use any energy (ATP) to move things through the membrane. Active transport requires some energy (ATP) to move things through the membrane.

The membrane also has proteins imbedded within the membrane. Some proteins are simple channel proteins, which assist molecules to enter or leave the cell. Other proteins are receptor proteins, which simply receive a signal from outside the cell, and relay the information to inside the cell (no a chemical signal is passing through the cell, inside of a molecule).

Procedure Part 1: Modeling the Cell Membrane

Purpose: What does the structure of the Cell Membrane look like?

Materials: 50 Cotton Swabs

1 Rubber Band

2 Pipe Cleaners of different colors

1 Drinking Straw

Scissors

1. Gather all the cotton swabs and place into a bundle. Then place the rubber band around the middle of the Q-tip sticks to keep them in this bundle.

2. Place a receptor molecule into the cell membrane.

a. Take one of the pipe cleaners and place it through the bundle of cotton swabs. Bend the top end of it into a circular shape. This shape represents how signal molecules bind to specific molecules. Only a circular-shaped molecule can bind with this receptor.

3. Place a carbohydrate chain into the cell membrane

a. Use a second pipe cleaner as a carbohydrate chain. Place it in the bundle of cotton swabs, just as in step 2, but don’t bend this pipe cleaner.

4. Place protein channels and pumps into the cell membrane.

a. First, cut your drinking straw in half. (This might already be done for you). Then, place both halves into different locations in the bundle of cotton swabs.

5. Answer Part 1 Questions. When you are finished answering the questions, then you may break apart your model to re-use the components for another class.

Part 1 Questions:

1. Sketch your model. Label: Phospholipid, receptor proteins, & protein channels.

2. How do the Q-tip swabs represent the phospholipid of the cell membrane? Which part is hydrophobic and which part is hydrophilic?

3. Which of the following materials would probably be allowed to bind to the receptor molecule you created in your model? (Beads, Marbles, Cube, Triangle). Explain your answer.

4. Roll the model (bundle of cotton swabs, straws, & pipe cleaners) between your hands.

a. Do the individual swabs move?

b. Without pulling the straw out can you move it between the swabs?

c. The cell membrane is known as a fluid mosaic model. Do you think this model represents that concept? Explain.

Part 2: Modeling Active and Passive Transport

Purpose: Demonstrate how active and passive transport work in a selectively permeable membrane.

Materials: 4 jumbo craft sticks Glue gun Rubber Bands

Ping-pong ball Marbles Beads Water

Procedure to build cell membrane model (Steps 1-2 may be done for you).

1. Glue four of the craft sticks together to make a square.

2. Wrap 5 elastic bands horizontally around Popsicle stick square. Wrap another 5 bands vertically around square, making a ¾ of an inch grid inside of the square.

3. Now try and drop the following items through your model plasma membrane. If they don’t make it pass the rubber bands, you may have to ‘help’ them through. Record your observations in the Data Table.

A. Bead

B. Marble

C. Ping Pong ball

D. Blow wind through your bands. This will represent Oxygen gas and Carbon Dioxide gas.

E. Using the pipette, 5 drops of water.

4. After you record your observation, determine if they require energy to move through the membrane. Record the data in the table.

Data Table:

|Item Name |Observations |Was Energy required? (Yes/No)|Type of transport (Active/ Passive)|

| | | | |

| | | | |

| | | | |

| | | | |

| | | | |

Part 2 Questions:

1. What size items passed through the membrane without energy? Why?

2. What size items passed through the membrane using energy? Why?

3. What function of a plasma membrane does this model show?

4. How does a selectively permeable membrane help maintain homeostasis?

This lab report needs: Title, Pre-lab Questions, Part 1 Questions, Data table (part 2), & Part 2 Questions

Modeling Cell membrane Questions & Data Table

Part 1 Questions:

1. Sketch your model. Label: Phospholipid, receptor proteins, & protein channels.

2. How do the Q-tip swabs represent the phospholipid of the cell membrane? Which part is hydrophobic and which part is hydrophilic?

3. Which of the following materials would probably be allowed to bind to the receptor molecule you created in your model? (Beads, Marbles, Cube, Triangle). Explain your answer.

4. Roll the model (bundle of cotton swabs, straws, & pipe cleaners) between your hands.

a. Do the individual swabs move?

b. Without pulling the straw out can you move it between the swabs?

c. The cell membrane is known as a fluid mosaic model. Do you think this model represents that concept? Explain.

Part 2 Data Table:

|Item Name |Observations |Was Energy required? (Yes/No)|Type of transport (Active/ Passive)|

| | | | |

| | | | |

| | | | |

| | | | |

| | | | |

Part 2 Questions:

1. What size items passed through the membrane without energy? Why?

2. What size items passed through the membrane using energy? Why?

3. What function of a plasma membrane does this model show?

4. How does a selectively permeable membrane help maintain homeostasis?

This lab report needs: Title, Pre-lab Questions, Part 1 Questions, Data table (part 2), & Part 2 Questions

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