“What Gets Through?” Selective Permeability With Coffee Filters

SAFETY CONSIDERATIONS: Lab coats and goggles should be worn throughout the lab. DO NOT EAT or DRINK any of the materials.

Every cell in the human body is surrounded by a cell membrane. This is a thin wall like structure that controls what enters and leaves the cell. The cell membrane is selectively permeable or semipermeable, meaning it allows certain substances to enter but not others. This can be seen as an example of when plants absorb nutrients from the ground and sift out bad chemicals, and in water purification systems that take out dirt, salt, or other chemicals. You could picture it as a school security guard, holding back the bad guys and keeping the children in school. This semipermeable membrane is the key to a healthy cell and a healthy body. It lets the right nutrients into the cell and expels waste so that the body can function at its best. Throughout this lab, you will learn about what types of substances are allowed through a semipermeable material and how it relates to cells in your own bodies.

Materials:

1. Lab Coat
2. Goggles
3. Clear beaker X2
4. Coffee Filter X6
5. Stir stick
6. Tap water
7. Food coloring
8. Corn Syrup
9. Salt
10. Timer
11. Rubber band
12. Vegetable oil
13. Gloves
14. table spoon
15. Milk
16. Sharpie

IF ALLERGIC TO ANY OF THESE MATERIALS, PLEASE USE GLOVES OR OTHER SAFETY PRECAUTIONS.

Hypothesis: Write your hypothesis for this lab

Purpose: Write the purpose of this lab

Place the coffee filter onto a beaker and secure it with a rubber band. Label the beaker test.

Pour the control water into another beaker and fill it until it reaches 50 ml. Then slowly pour the water into the coffee filter and record observations. Time the number of seconds the water diffuses through the coffee filter.

Remove the coffee filter and replace it with another one. Rise the beaker, then pour 50 ml of water, and add 1-2 drops of food coloring. Stir with the stir stick, and slowly pour the solution into the coffee filter. Record observations. Record time.

Remove the coffee filter and replace it with another one. Rinse the beaker and remove any other solution down the drain. Rinse the stir stick. Add 50 ml of water to the beaker, along with 2 tablespoons of salt. Stir until fully dissolved. Slowly pour the solution into the coffee filter. Record observations. Record time.

Remove the coffee filter and replace it with another one. Rinse the beaker and remove any other solution down the drain. Rinse the stir stick. Add 50 ml of milk. Slowly pour the solution into the coffee filter. Record observations. Record time.

Remove the coffee filter and replace it with another one. Rinse the beaker and remove any other solution down the drain. Rinse the stir stick. Add 50 ml of corn syrup. Slowly pour the solution into the coffee filter. Record observations. Record time.

Remove the coffee filter and replace it with another one. Rinse the beaker and remove any other solution down the drain. Rinse the stir stick. Add 50 ml of oil to the beaker. Slowly pour the solution into the coffee filter. Record observations. Record time.

Now the lab is finished, and observations are made. Rinse all the equipment thoroughly with water and soap, and put them onto the drying rack. All solutions can go down the drain except for oil; it must be discarded in another container. Wipe the table clear with a spray bottle and paper towel. YOU'RE ALL DONE!

A selective membrane is in the plasma membrane or the membrane of the cell. Plasma membrane is the out layer of the cell that holds the cells shape. This membrane is essential for the transportation of nutrients and waste into and out of the cell. There are many other factors that contributes what gets through a plasma membrane. For example, the size, charge, and type of molecule are all important factors. Small and uncharged molecules like oxygen and carbon dioxide can move into the membrane easily, while larger or charged molecules like sugars or positive or negatively charged ions cannot pass through on there own, and need help from proteins in the membrane. This membrane keeps the cell safe and balanced, making sure it gets what it needs and keeps out harmful substances, just like a filter or gate that protects what’s inside.

Some liquids in your experiment passed through the coffee filter easily, while others didn’t. What do you think caused these differences? Was it the size of the particles, how thick or watery each liquid was, or something else?

What are some errors that occurred during this lab? How can this change the results, and what can be done to the lab to be better and error-free?

Why do you think thicker substances like corn syrup or oil didn’t pass through the filter as easily as water or salt water?

If the coffee filter represents a cell membrane (which it does), which substance in this experiment would best represent nutrients that can enter a cell? Which would represent substances that are blocked? Connect to the cell membrane in answer.

How does this lab show the connection to a semipermeable membrane and the cell membrane? How would this be helpful information or a helpful process on how cells control what enters and leaves to stay healthy?