Every day your body is exposed to thousands of germs, and you do not get sick from them because of your immune system. Every time you do get sick because of a germ, your immune system works to get rid of it and then it remembers how to fight the infection if the same germ comes again. Usually the older you get, the more germs you become immune to, which is why kids get sick a lot more often than adults do.
One of the most important parts of the immune system is your integumentary system- your skin. The skin is usually the first defense your body has against disease. You know how you put plastic wrap over leftovers to keep them fresh enough for later? Well, your skin is like a plastic wrap to keep germs from getting into your body.
DEMONSTRATION:Cut an apple in half and wrap one half with plastic wrap. Drop a drop of food coloring on each half of the apple. Notice what happens to each half. Discuss the difference.
The epidermis (your outside layer of skin) has special cells which warn the body about incoming germs. Glands in the skin also make substances that can kill some bacteria. This means you don't get infections on your skin unless your skin is damaged, such as by a cut or scrape.
Your nose, mouth and eyes are the next point of attack. The mucous membranes, which line the mouth, throat, lungs and bowel, act like a barrier to germs, just as the skin does. The mucous that is made in your nose, throat and lungs traps bacteria, viruses and dust. Saliva in the mouth and the tears which wash your eyes have special enzymes (chemicals) in them which break down the cell walls of many bacteria and viruses. Acid in your stomach kills most germs and starts to digest your food.
Your lymphatic system works with your immune system to fight invaders. Lymph is a clear fluid that is very similar to blood plasma, the clear liquid in blood. In your blood you have red blood cells and white blood cells, but in lymph there are only white blood cells. There are several different types of white cells which work together to seek out and destroy bacteria and viruses. The lymph flows through lymph vessels (kind of like blood vessels). It is carried to all the parts of the body, picking up the fluid around cells and carrying it back to large veins near the heart. It also carries the white cells to the places that they are needed. Antibodies, which are made by special white blood cells called lymphocytes, attach to invaders so that the other white blood cells can destroy them.
Dotted along lymph vessels, like beads on a string, are small swellings called lymph nodes. Sometimes bacteria or viruses that have entered the body are collected by the lymph and passed on to the lymph nodes where they are filtered out and destroyed. Lymphocytes are also grown in the lymph nodes. Your doctor can sometimes tell if you have an infection by checking the lymph nodes in your neck and under your arms to see if they're swollen. If they are, it shows that they are working to get rid of bacteria or viruses.
While other systems of your body have major organs you can dissect and remove from the body, your immune system is relatively invisible and made of many types of immune cells. You can't really "see" your immune system, but sometimes you can see it working.
Have you ever had a runny nose? If your nose is running and your feet smell, you must be upside down! Right? Or maybe your runny nose is just a clue that your immune system is fighting a cold. Runny noses, fevers, and swelling are all examples of ways that our immune system responds to problems.
Remember I talked about the mucus that is made in your nose, throat and lungs which traps bacteria, viruses and dust? Normally, your nose and sinuses make about a quart of mucus a day. That's a lot! But when cold or flu germs enter your body, your immune system makes even MORE mucus to help wash the germ invaders out.
Mucus is made mostly of sugars and proteins. The protein is what makes it so stretchy and sticky. I've brought along some fake snot I made out of corn syrup and gelatine. These aren't the same things your mucus is made out of, but they are a type of sugar and protein. I also brought along some cookie crumbs so we can pretend to catch some "dust and germs" with our snot. Do you know what happens the mucus in your nose gets full of dust? It makes a booger!
So, you can take your fake boogers home, and you can remember one way that your immune system protects you from germs. Or you can even eat them if you want. Just don't eat your real boogers, OK?
Do you know the difference between boogers and broccoli?
Your friends don't eat their broccoli.
- 1/2 cup of water
- 3 envelopes of unflavored gelatin
- 1/2 cup of light corn syrup
- Measuring cup
- Kettle or pan
- Fork
- Cookie crumbs
Heat 1/2 cup of water until it boils and remove from the heat. Pour in 3 envelopes of unflavored gelatin, wait a few minutes until it softens and stir with a fork. Add 1/2 cup of corn syrup. Stir with fork and lift out long strands of “mucus”. Allow children to use their "snot" to pick up cookie crumbs. After the experiment, dispose of the "boogers" in the garbage.
Note: As the water cools, you may need to add a spoonful or two of water.
Grow Some Good Bacteria
Generally, when people think of "bacteria," they think of harmful germs. However, not all forms of bacteria are bad! You can enjoy a tasty product of good bacteria by making a batch of yogurt at home.
- One cup of plain, unflavored yogurt that has live cultures (If it contains live cultures, it will say so on the container.)
- 4 cup milk
Slowly heat milk until it is hot but not boiling or scalding. The temperature should be around 95-120 degrees to kill some of the harmful bacteria. Cool slightly, until milk is warm, and then add the yogurt. Put the mixture in a large bowl (or glass jars) and cover. Make sure that the bowl or jars are sterilized before using by either running them through the dishwasher or washing them with very hot water.
There are two different methods for culturing the yogurt mixture: You can put the covered bowl or jars into a clean plastic cooler and fill the cooler with hot water to just below the top of the culture containers. With this method, you will need to occasionally refill the cooler with hot water, so that the temperature of the yogurt stays consistent.
The other method is to wrap the containers in a heating pad and towels, setting the heating pad on low to medium heat. Check the mixture after heating for 3 1/2 to 4 hours. It should be "set up," having a smooth, creamy consistency similar to store-bought yogurt. If the mixture is not set up yet, heat it for another 1-2 hours.
When it is the right consistency, add some flavoring—such as vanilla extract or berries—and store the yogurt in the refrigerator. It should keep for a couple of weeks. For safety, we suggest that you do not eat any yogurt that has separated or has a non-typical consistency.
This experiment comes from the Home Science Tools website. Please visit their Bacteria Experiments Guide for more ideas.
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