Science Experiments With Mold

Erin Coleman, R.D., L.D.
Mold growing on food

Growing mold for science experiments will capture your audience's attention, and studying mold is an excellent way to learn more about ecology and biology. Whether you're looking to grow mold on food, or want to try a more adventurous project like slime mold, make sure to use normal precautions such as using gloves when handling samples.

Moldy Food Project

This experiment compares how fast mold grows on different types of foods kept in many American homes. Some of the foods are generally kept in refrigerators to extend shelf life, while others are commonly stored at room temperature. This is a great project for a first-time science fair participant, and kids can understand the concepts as young as kindergarten. This one requires advanced prep though, as the food will take at least a week to grow any mold, and it will take several weeks before you will see lots of mold growth.

Materials

  • One slice of bread
  • One slice of American cheese
  • One strawberry
  • One tomato (or other food of your choice)
  • Four paper plates

Instructions

  1. Place bread, cheese, strawberry, and a tomato each on four separate plates.
  2. You'll want to label the plate with the date.
  3. Put plates of food in a pantry or cabinet.
  4. Check foods daily for signs of mold.

Recording Your Results

In your log book, you'll want to record your results. While there are no specific ways to do this, the following suggestions will help:

  • Take pictures of each plate every other day. This way, at the end of the project, you can see the development of mold over time.
  • Hold a coin next to the mold as you take a picture. Doing this will help those who are seeing your project compare how big or small the mold is.
  • Other questions you should be considering include:
    • Are there foods that don't grow mold? Why do you think that is?
    • What are ways that people inhibit mold growth now?
Cheese slice
mold on tomato
Mold on bread
mold on stawberry

Going Further

This experiment shows that certain foods grow mold faster than others, which is one reason why these foods are often kept in the refrigerator. What are other ways that people keep mold from growing? To take this experiment a step further, change the conditions of your experiment:

  • Put all the food in the fridge. While refrigeration slows mold growth, it doesn't stop it completely. How much longer does it take your food to go moldy if it's kept in the fridge.
  • Did you have food that didn't grow mold? If so, why do you think that happened? (Hint: look to see what kinds of preservatives are in the food that didn't grow mold.)
  • What other ways are there to prevent mold growth? What if you add salt or a citric acid to the food? Will that inhibit the growth of mold?

There are lots of different variations to this experiment, so make sure that you plan well in advance so you have time to try a variety of things.

Petri Dish Mold Experiment

Mold is a type of fungi, which is a living organism not classified as an animal or plant. Mold feeds on organic plant or animal matter, and requires mold spores, food (carbon-containing organic substances), moisture and proper air temperatures to survive and reproduce. For this experiment, you'll test different surfaces near and around your home for the presence of mold spores.

The experiment is best done with middle or high school students who have learned how to work with agar and petri dishes. While you may want to grow your samples for awhile, you should start to see mold within a week of collecting a sample.

Materials

Basic Instructions

It's important to keep the plates as sterile as possible. Consequently, read the directions first so you have a thorough understanding of what you're going to do, then work as quickly as possible anytime you have a swab or dish uncovered. Work with one dish at a time, collect the sample, and then place the Petri dish in the spot where you'll keep them for observation before going on to the next dish.

  1. First, label the Petri dish, on the bottom (so you can see the results without handling the dish), using masking tape and a permanent marker. You'll want to note the date, and where the sample was taken.
  2. Take your first Petri dish, with the lid on, and a still-wrapped cotton swab to the area that you plan to swab.
  3. Keep the lid on your Petri dish until after you've swabbed the surface.
  4. Unwrap the cotton applicator and quickly, but thoroughly swab your chosen surface. After you've swabbed the surface, hold the applicator in one hand and quickly remove the Petri dish lid.
  5. Gently but thoroughly swipe the surface of the agar in your dish and replace the lid.
  6. You may find it helpful to place to small pieces of tape on the side, or to secure the lid of the Petri dish with a rubber band. The lids can come off easily, and if that happens, your experiment may be ruined.

Observing Your Mold Growth

You'll want to observe your mold growth at intervals. While there are no hard and fast rules as to how to do that, you may want to try the following ideas for your project:

  • Take a picture every day and make a time lapse video. A video is a great way to show growth and changes, although make sure that you note in the video how long of a time period the video covers.
  • Record your observations in a log book. Draw pictures of your mold as you go along. You can do this easily by tracing the edge of petri dish on a piece of paper. Next, measure each mold spot and draw it on the circle you've created on your paper.
  • Observe just one spot. While you want to record all of your observations, it's also okay to make special note of one particular spot. Make sure to measure it with a small ruler that has mm on it.
mold in petri dish

What the Experiment Shows

This experiment demonstrates the ability of mold to grow from spores on different surfaces throughout your house and on your body. It shows how dirty certain surfaces really are, demonstrating the importance of hand washing and thorough house cleaning.

Slime Mold Project

Slime mold is a particular type of mold that almost acts like amoebas to eat. What's fun about working with slime mold is that the mold actually changes and responds to the conditions you introduce - so there is a lot to observe. This project is appropriate for high-school aged students.

Materials

  • Two plate cultures of physarum polycephalum plasmodium
  • Slime mold food (they are particularly fond of oatmeal)

  • Eye dropper

  • Gloves

  • A 'toxin' such as nail polish remover or vinegar
  • Lamp

Instructions

  1. Put on your gloves to avoid contamination during the experiment.
  2. Using a permanent marker, divide your petri dish into quadrants. This is to make quantifiable observations easier.
  3. Keep the petri dishes covered at all times, unless you're dropping food or toxins into them.
  4. Quickly uncover a petri dish to drop in food on the opposite side of where your culture currently is; then place the lid back on. You'll want to record any observations over the course of several days.
  5. Next, using an eye dropper place a toxin (nail polish remover or vinegar) into the other petri dish, and record your observations.

Observing Your Slime Mold

Slime mold is especially satisfying as it is easy to cultivate. The best way to record your observations is to do so by measuring distance traveled and drawing pictures. Use the quadrants you drew and a ruler to recreate relatively reliable descriptions and drawing.

Going Further

There are several variations of slime mold experiments. If you have extra mold around, you can try one of the following labs to take your experiment to the next level. As a side note, make sure that you observe for the next week after you try a new variable.

  1. What happens when you introduce physarum to light? Cover one part of the petri dish in aluminum foil and shine a light onto the other half. How do the physarum react?
  2. Introduce a toxin such as nail polish remover or vinegar. Add a swab of the toxin near (but not on) the physarum - what does it do?
  3. You can 'teach' your slime mold how to go through a maze! The video below is a time lapse sped up. Use a new petri dish with the appropriate agar, but no slime mold. Create a maze out of any kind of plastic. Introduce your slime mold on one end of the maze and the food at the end of the maze like below:

What the Experiment Shows

Slime mold is a type of mold that acts more like an animal than a fungus. It moves together in groups, searching for food and away from toxins and light (which can dry out the mold, preventing movement). Slime mold grows quickly when active and eating food. It can even secrete chemical signals to help avoid toxic substances, or reconnect as a group after being separated.

Why Grow Mold?

Science experiments with mold show how different environmental conditions like temperature, type of food medium or surface, and moisture, are conducive for mold growth. Because mold spoils food and can make you sick, knowing how to reduce or prevent mold growth is an important concept to learn about.

Science Experiments With Mold