Our immune system is made up of different cells and organs in our body that normally defend us against germs and harmful microorganisms. We are all constantly exposed to microorganisms, or microscopic organisms, some of which can make us sick. Any microorganism that makes us sick is called a pathogen. Pathogens include harmful bacteria, microscopic fungus, viruses, and more. If a pathogen infects us, we become sick from that pathogen, or get an infection.
Our immune system goes through a process called the immune response to fight off pathogens. White blood cells (i.e., leukocytes) do most of the work. White blood cells must find the pathogens in our body and tell them apart from human cells. (This process is referred to as self/non-self recognition, and if it fails, it can cause autoimmune diseases, where the immune system attacks the body instead of pathogens, or it can cause an infection.) The white blood cells then make antibodies, tiny particles that grab, or bind onto, the pathogen. When antibodies bind the pathogen, this stimulates white blood cells to destroy the pathogen. Lastly, some white blood cells leave a memory cell behind. Memory cells "remember" the specific pathogen encountered, so they can mount a larger and faster immune response if they encounter the same pathogen again.
During the immune response, antibodies (in blue) bind onto a pathogen (a bacterium here, in red). When the antibodies bind the pathogen, this stimulates white blood cells to destroy the pathogen. Note: This simplified diagram is not to scale.
In this science activity, students will use magnets, iron filings, and salt to make a model of the immune system in the human body and investigate how memory cells help the body fight off an infection.
This science activity can serve as a starting point for a variety of science and health discussions. A few questions can be used to start a discussion:
What common pathogens do we encounter?
How do antibodies work in the immune response?
What do memory cells do? Why are they important?
What do the different parts of your model represent in the immune response?
What causes an autoimmune disease?
How are autoimmune diseases treated?
Needed for preparing ahead:
Magnetic tape, 1-inch width (at least 3 inches long). Magnetic tape is available from craft stores or online at
Plastic wrap (about 1 foot)
Twist ties (3)
Needed for each demo or small group at the time of the science activity:
Glass jar with lid, 16 oz. size (1). A smaller or larger sized glass jar (with lid) would work too, but the amount of iron filings and salt will need to be adjusted accordingly.
Table salt (1 cup)
Iron filings (1 tbsp.). Iron filings are available from educational material suppliers or online at
Piece of paper
You need only a few simple household materials and some iron filings to do this fun science activity.
What to Do
Prepare Ahead (< 10 minutes)
Cut the magnetic tape into three squares, each 1 by 1 inch. Leave the paper strip on the tape so the adhesive is covered.
Cut the magnetic tape into three squares, each about 1 by 1 inch. This picture shows the sides of the magnets with the paper covering their adhesive backs.
Cut the plastic wrap into three squares that are each about 4 by 4 inches.
Put each magnetic tape square in the middle of a plastic wrap square. Place the magnet so that the adhesive side (covered by paper) is facing up.
Place a magnetic tape square in the middle of a plastic wrap square.
Pull the ends of the plastic wrap together around each magnetic tape square, twist the plastic wrap ends together, and then put a twist tie around the ends to hold them securely. Make sure there are no openings in the plastic wrap surrounding any of the magnets (so that salt or iron filings cannot get through and reach the magnetic tape).
Gather the plastic wrap around the magnetic tape square and secure the ends of the plastic wrap with a twist tie.
You should end up with three magnetic tape squares, each enclosed in plastic wrap bound together with a twist tie.
Science Activity (10-20 minutes)
Each classroom demo or small group should have a glass jar with a lid, 1 cup of salt, a measuring cup, a measuring tablespoon, 1 tablespoon (tbsp.) of iron filings, a piece of paper, and three magnetic tape squares wrapped in plastic and secured with a twist tie.
Help students measure out 1 cup of salt and pour it into the glass jar. The jar should be about half full with salt. Then have students measure out 1 tbsp. of iron filings and add it on top of the salt in the jar.
Have students pour 1 cup of salt and then 1 tbsp. of iron filings into the jar.
Have students put the lid on the jar tightly and then mix the salt and iron filings together by flipping the jar upside down and then right-side up again. Have them do this about ten times, about one flip per second, or until the iron filings appear evenly dispersed throughout the salt in the jar. Ask students to examine the jar.
After mixing the iron filings and salt together, the iron filings should appear only as specks throughout the jar.
Explain to students that, in their model of the immune response, the jar represents the human body. The salt represents human cells and the iron filings represent pathogens (many copies of the same pathogen). The human body is infected with the pathogens. Each magnetic tape square (surrounded by plastic wrap) represents many antibodies made by the immune system to fight the pathogens. Be sure to let students know that their model is not to scale, because in reality the cells would be much larger than the pathogens, which would be much larger than the antibodies. (Also, normally many antibodies bind onto a single pathogen.)
Have students take one of the antibody models (the prepared magnetic tape squares) and put it in the jar of salt and iron filings (resting on top of the mixture). Then have them put the lid back on the jar tightly and again flip it ten times.
Have students set an antibody model in the jar, put the lid on the jar, and flip it about ten times.
Now ask students to carefully remove the antibody model from the jar. They may need to carefully tilt the jar to grasp the antibody. Tell them to only grab it by the twist tie or twisted plastic, but not to touch where the iron filings are. As they take it out of the jar, have them gently turn the antibody model upside down so that any salt trapped in the twisted plastic wrap falls back into the jar. They may need to gently shake it to do this, but tell them not to shake it so hard that iron filings are knocked off the magnet.
Ask students to examine the antibody model. Ask them if it looks like more iron filings are stuck to the magnet than salt, and if it looks like the antibody is specifically binding onto the pathogens (the iron filings).
Have students look at the magnet antibody model to see if more iron filings are stuck to it than salt.
Now have students hold the antibody model over the piece of paper, untie the twist tie, and open up the plastic wrap surrounding the magnet. Have them carefully position the plastic wrap so that only the iron filings and salt fall onto the paper. Again, ask students to observe what fell onto the paper.
Have students carefully remove the plastic wrap from the magnet so that the iron filings and salt fall onto a piece of paper.
Once they have finished making observations, help students carefully funnel the iron filings and salt on the paper back into the jar and secure the lid. Ask them to again mix the iron filings and salt together in the jar by flipping the jar ten times.
Now ask students to put all three antibody models in the jar together. In their model, this represents the immune system's memory cells making more antibodies when they encounter the same type of pathogen again. Have students put the lid tightly on the jar and again flip it ten times.
Have students put all three antibody models in the jar together, put the lid on the jar, and flip it about ten times.
Then ask students to take each antibody model carefully out of the jar, one at a time, as they did before. Again, they should tilt the jar carefully to grasp the antibody models, taking care not to knock off iron filings bound onto the magnet, and gently turn the antibody models upside down and shake each a little so that trapped salt falls back into the jar.
Ask students to examine each antibody model. Ask them how each antibody looks similar or different from the first antibody model. Be sure to ask if it looks like each antibody has more, less, or about the same amount of iron filings and salt stuck to it as the first antibody did.
Then have students hold each magnetic tape square over the piece of paper, undo the twist tie, and open up the plastic wrap surrounding the magnet. Have them carefully position the plastic wrap so that only the iron filings and salt fall onto the paper. Again ask students to observe what fell onto the paper, and whether it is more, less, or about the same as what fell from the first antibody model. You can ask them what they think this says about why the immune system creates memory cells.
When one magnetic tape square (representing an antibody) was mixed with the salt and iron filings in the jar, there should have been many more iron filings (representing pathogens) than salt grains (representing human cells) stuck to the magnet, showing that the antibody is specifically binding onto pathogens. When three magnets were in the jar together, about the same amount of iron filings (and salt) should have stuck to each magnet, representing the immune system making more antibodies and launching a much larger attack against pathogens when the memory cells "remember" them.
For Further Exploration
This science activity can be expanded or modified in a number of ways. Here are a few options:
Students may have seen that about the same amount of iron filings and salt was captured using each antibody model, but is it exactly the same amount? Students could quantify their results by weighing the iron filings and salt (that dropped from each magnet) on a scale.
This model could be tweaked to model differences in the immune response. For example, if students want to investigate antibodies that are more effective, they could try using larger or stronger magnets. Alternatively they could make more plastic-wrapped magnetic tape squares and try more than three such antibody models at a time. Is there a certain number of antibodies at which their results change?
Students may have noticed that the antibody models capture a small amount of salt. In the model, this would represent the antibodies attacking human cells in an autoimmune response. Students could investigate the autoimmune response by quantifying how much salt was captured compared to the total amount captured. To separate the salt from the iron filings, they could spread them both over a piece of paper and hold a plastic-wrapped magnetic square directly above them to pull out the iron filings and then deposit them onto another piece of paper. Students could then weigh each separately on a scale. How much of each (iron filings and salt) is there? What percentage does each represent of the total?
Teisha Rowland, PhD, Science Buddies
Sponsored by a generous grant from Amgen
You can find this page online at: http://www.sciencebuddies.org/science-fair-projects/Classroom_Activity_Educator_Immune_Response.shtml
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