Some of the most interesting science is in your kitchen! You can find a fascinating variety of life: mold, yeast, and mushrooms, all grouped together as fungi. In this article we’ll look at ways you can find out more about these organisms.
For any experiment, there’s a key that can be really helpful. Have you heard of the scientific method? Basically, you start with a question, like “what happens to this if I add that?” Then based on what you read about a topic, come up with a hypothesis, a prediction of what you expect to happen in certain conditions. Next, you can experiment to find out if your hypothesis is right! For the most accurate results, you need to control the experiment’s variables (for a mold-growing project like these, include type of bread, room temperature, and amount of light). Be sure to use at least one “normal” piece as your control, so you have a standard for comparison.
Once you’ve completed the experimentation stage, look at your predictions again. Do you need to do more research and change anything, based on your results?
What Are Fungi?
There are five “kingdoms” of living organisms: plants, animals, fungi, and tiny bacteria and protozoa. Mushrooms, molds, and yeasts are all in the fungi kingdom. Although sometimes they look similar to plants, fungi do not produce their own food through photosynthesis. Fungi range in size from just one tiny cell to several inches tall.
Fungi are important decomposers, eating up dead leaves and other rotting organic material. Unlike when you eat and your food is digested (broken down into tiny parts) inside your body, fungi digest their food outside of their bodies and then absorb it into their cells. Fungi have many different means of reproduction, but all are able to reproduce by forming spores, which are spread out and develop into more fungi.
Many fungi are harmful, causing diseases like athlete’s foot and Dutch elm disease (in trees). But some fungi can also be used for saving lives. Perhaps the greatest use of fungi is in the treatment of bacterial diseases that used to be deadly, such as scarlet fever and pneumonia. Starting in the late 1920s, scientists discovered that a type of mold, Penicillium notatum, prevented the growth of some bacteria. They created an effective antibiotic, called penicillin, to treat bacterial diseases.
As you know if you’ve ever left bread or fruit on the counter for too long, mold is easy to grow! This is because mold produces a lot of spores and they spread easily. All you need to grow mold is 1-2 pieces of bread and some scraps like fruit peels, carrot shavings, or coffee grounds.
Mold needs light and oxygen to grow. They also do best at room temperature. Based on what you’ve found out about mold, what do you expect to be the best environment in your house for growing it? What about the worst? How do you think heat and cold will affect growth?
As you experiment with mold, follow these safety rules! Do not touch mold or bacterial growth with bare hands. (Use gloves if you want to touch the mold.) Be sure to wash your hands with soap and water after holding a moldy specimen, even if you don’t touch the mold directly.
In this experiment you’ll compare mold growth on bread and on other food at the same time. First, get four pieces of bread (or divide two in half). Splash each of the pieces with water to dampen but not soak them. Place each piece in an individual plastic bag. Don’t seal the bags completely, so some air can still get inside. Now place two of the bags in a spot where they will get some sunlight. Place the other two in a spot where they will get less light, but the temperature is about the same as in the other spot.
Next, put the food scraps (either all the same kind or a mixture) on two paper plates. Set one next to the first set of bread specimens and the other next to the bread in the darker spot.
After 2-4 days you should see some spots of mold growing. Mold spores grow on stalks, kind of like mushrooms but on a smaller scale. These raised spores are what give mold on food a fuzzy appearance. Mold is usually blackish on starchy foods like bread, and a fuzzier blue or green on fruit.
Wait a couple more days until there’s a large area of mold on the food. Which set of bread has the most growth on it, the one in the light or the one in the dark? What about the scraps? Do some scraps have more mold than others?
As you discuss what you see, you might also want to write down your observations and make sketches. Use a magnifying glass or a microscope, if you have one, to look at the mold spores close up. What do you see? (To view under a microscope, use a sharp knife to carefully scoop up some of the mold and set it on a microscope slide. Look at the mold under low and then high power.)
For further study, come up with your own experiments that help answer the following questions: Which foods are most susceptible to mold, ones high in starch or high in protein? What difference does the presence of sugars make? If mold grows best in a slightly acidic environment (5-6 pH), how might you make it grow faster? Think about what foods are more acidic; for instance, vinegar and lemon juice are highly acidic at 2-3 pH, while apples have an acidity of 3-4 pH.
How Can You Prevent Mold Growth?
Almost every processed food has some kind of preservative in it, to keep it from spoiling. White bread usually has far more preservatives than regular wheat bread. Fruit and vegetables are harder to preserve, although often apples are coated in a thin protective wax. Refrigeration often keeps food preserved for at least several days, because the cold temperature inhibits mold and bacteria growth.
Use the peelings from 2-3 apples, pears, or oranges for this experiment. Put an even amount of peels on four paper plates and set them in a place with some sunlight. Now sprinkle about a teaspoon of salt over the peels on one plate, and label the plate “salt.” Do the same for another set, but this time with sugar. For the last one, choose your own “preservative” – it might be from the spice rack or it could be a mild household cleaner from under the sink! Which set of treated peels do you expect to be most resistant to mold growth? Which do expect to have the most growing on it? Observe mold growth on each after 2-3 days. Look again each day after that for the rest of the week. How does the mold compare on each? Was it how you predicted it would be?
Have you ever made bread? For non-sweet breads, usually you have to mix active dry yeast with water and then mix it with dough and let it rise. The yeast breaks down sugar molecules in the dough and converts it to carbon dioxide (CO2) gas, alcohol (which evaporates as the bread cooks), and water. The CO2 is what causes the bread dough to rise. Look at a piece of bread, homemade or store-bought. Do you see the “holes” in it? These are caused by bubbles of CO2 from the yeast.
What difference does temperature make to yeast growth? Test this by adding a teaspoon of active dry yeast to a cup of cold water and a teaspoon to a cup of warm (but not boiling) water. Observe them both. How does the yeast act in each? Use your eyes and your nose! In the warm water, the yeast turns slightly foamy almost instantly and gives off a strong “fermenting” smell. As they begin to reproduce, the round yeast cells begin to dissolve in 1-2 minutes and form a thick, sticky coating on the water. Stir the yeast into the water and see what happens. It will form globs of yeast that stick to the spoon. Now compare the yeast in the cold water. In the same amount of time, it will also form a coating on the water’s surface, but without looking dissolved. You’ll still see lots of dry yeast on top, and when you stir the water, the yeast is not so sticky. In the beginning, there’s also less of a smell, as the spores take longer to begin fermenting. From this, you might conclude (correctly) that yeast is most active in a warm environment!
Don’t Forget Mushrooms
Although you probably won’t be able to see them on store-bought ones, mushrooms have long root-like hairs called mycelium that take care of digestion and absorption. This is actually the main part of the mushroom! The part we’re used to seeing, a stem or stalk with a cap on the top, only grows at a certain part of the mushroom’s development. These parts are still important, though! They form the “fruiting body” that grows out of the mycelium and release spores, so that the mushroom can reproduce. Underneath the cap are gills, which hold the spores.
Get a mushroom from the grocery store so you can observe the different parts of the fruiting body. First examine how the outside looks, then slice the mushroom down the middle. Does the inside look like you expected it to? Why do you think mushrooms and other fungi have so many spores?
If you’d like to see the amazing variety of mushroom species, visit www.mykoweb.com for pictures.
These activities are just a taste of the exploration you can do in this one kingdom, fungi. If you have more questions about mushrooms, mold, or yeast, do some research and then design experiments to help you answer them!
This article was originally published in the Jan/Feb ’06 issue of Home School Enrichment Magazine. For more information, and to request a free sample issue, visit http://HomeSchoolEnrichment.com