Bread fungi and mold microbes belong to the fungi phyla zygomcota. When these microbes appear on food, the food begins to decay and rot. This rotting action is observed on foods after a few days; the time depends on the amount of preservatives included in the food. Refrigeration protects foods that are subject to rapid growth of these microbes by slowing the growth of the microbes.
Fungi and mold microbes live all around people. They are everywhere and on almost everything. These microbes are in the air, water, soil, food, on clothes, on hands, and on desks. These microbes are too tiny to see with human eyes. This is why scientists study these microbes using a microscope.
Fungi and Mold Growth
Mold growing in thin transparent threads on the slice of bread is called a mold garden. The garden looks like a tangled spider web. At the ends of these branches are little round balls. These balls are hollow round cases and each one is filled with tiny seeds called spores containing seeds.
In 2-3 day old mold students begin to see the spores on the garden. The spores are the black substances sitting on top of the threads. Each black ball or spore contains more than 20,000 smaller spores. Mold has no color even though their spores make them appear to have different colors, because the spores in the cases have color.
The 3-4 day old mold produces hundreds of millions of new spores. These spores fall onto moist food, sprout threads of their own, and give rise to new spores. Mold grows better on whole wheat bread, because white bread has little nutrition to support mold growth. Additional information is available at bread mold fungus.
Investigation of Rotting Food
This investigation involves students problem solving and using science process skills as they complete this investigation. Students also follow the tenants of the scientific method and problem-based learning as they solve the mystery of what causes food to rot. Using Wikis in science allows students the opportunity to share their projects with students in other classrooms, schools, and with their parents.
Materials (per group)
- Microscope
- Two slices of whole wheat bread
- Water
- Eye dropper
- Two paper plates
- Plastic wrap
- Paper tape
- Digital Camera
- Computer
- Wiki page
Procedures
Day 1
- Place a piece of bread on each paper plate
- Moisten the bread with several drops of water (do not soak the bread)
- Allow the bread to be open to the air for 30-45 minutes
- Cover the bread and paper plates with plastic wrap
- Label each plate with a one or two using tape
- Store plate one in a warm place
- Store plate two in a cool place
Day 2
- Remove bread plates one and two and record your group’s observations; include the use of a microscope and pictures to collect data.
- Place bread plates back in same location.
Day 4
- Same procedures as Day 2.
Day 5
- Remove bread plates one and two and record your group’s observations; include the use of a microscope and pictures to collect data.
- Student groups upload their pictures, observations, data, findings, and conclusions to their page in the class Wiki for presentation to the class.
Student Questions
Day 2
- What did your group observe?
- Where there any differences between the plates?
Day 4
- Same questions as Day 2.
Day 5
- Same questions as Day 2.
After Student Presentations
- Why was the bread exposed to the air for 30-45 minutes before sealing with plastic wrap?
- What happens if the bread is placed in a hot place, instead of a warm place?
- What happens if the bread is placed in a cold place, instead of a cool place?
- What happens to the bread if the fungi and mold continues to grow?
- What other folds have they observed rotting due to mold and fungi growth?
Making Connections
Proteins in the microbes called enzymes aid the breakdown of food through the growth of new microbe cells that create energy for new growth. These enzymes work best at warm temperatures. If the temperature is cold, enzymes action slows the breakdown of food and creation of energy. The microbes are not killed by cold; however, they grow much more slowly.
If the temperature of the food is increased to 212 degrees Fahrenheit/100 degrees Celsius, most fungi and mold microbes are destroyed. Some still survive and begin to grow after the food cools. This is why food rots even after cooking; time to rot is dependent on the properties of the food.
David R. Wetzel - Dr. David Wetzel's experience includes more than 25 years in continuing, adult, and teacher education.
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