A Moldy Experience

Contributor: Jay Gregorio. Lesson ID: 13356

Don't eat that bread! It has mold all over it. But what about foods like cheese that need mold? Is mold good or bad? How does it grow? What does it do? Find all the answers here!


Chemistry, Life Science

learning style
Auditory, Visual
personality style
Grade Level
High School (9-12)
Lesson Type
Dig Deeper

Lesson Plan - Get It!

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You are hungry and decide to make yourself a sandwich. When you pull out the bread, however, you see this:

moldy bread

Ugh! Moldy bread.

  • Do you remove the moldy parts and eat the rest of the bread, or do you throw it all away?
  • Why?

Let's find out!

Throw it all away!

Even the parts that look clean will be full of the microscopic organisms that cause mold. You do not want to ingest unwanted fungi!

What Are Fungi?

Fungi are living organisms that are not classified as plants but rather have their own classification.

Unlike plants, fungi cannot manufacture food through photosynthesis, and their cell walls are made of chitin instead of cellulose. However, their eukaryotic cells are complex like those of plants and animals.

Fungi vary in size from microscopic to as big as 3.4 miles across!

These unique organisms grow in all parts of the earth -- land, air, water, and even in plants or animals.

There are different types of fungi, each with its own characteristics that make it useful or harmful to humans.


Mushrooms are the spore-bearing fruiting body of the fungus. They are typically produced above ground in soil or on parts of other plants where the environmental conditions support their growth.

Not all mushrooms are edible. Some of them are poisonous!


Molds are formed on filaments called hyphae which grow rapidly on old bread, fruit, or cheese. They survive in moist environments where their lightweight spores can be carried by air to spread on other parts of the food where they started growing.

dry yeast

Yeasts are single-celled organisms that are popularly used to raise bread. They need food such as sugar and starch to survive.

When yeasts undergo fermentation, they convert their food into carbon dioxide and alcohol. The carbon dioxide is the reason behind the rising of the bread.

How Do Molds Grow?

Because molds are not plants, they do not grow from seed. They produce tiny spores that float in the air. If they land on a moist surface, the spores can start growing!

Unlike plants that undergo the process of photosynthesis, molds don't make their own food. Instead, molds feed on the food where they are found to grow and spread quickly.

Molds release chemicals that make the food rot and break down. Once broken down, molds absorb the nutrients helping them reproduce. This is the reason why it isn't a good idea to eat around the mold on bread!

Watch Never Eat The 'Clean' Part Of Moldy Bread from Science Insider:

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Helpful Molds

The growth of molds is not always a bad thing. In fact, molds are valued as nature's natural recycler.

Every living organism on Earth returns to the soil when it dies. Molds help break down this organic matter, making the soil more fertile.

There are also many industries -- from food to healthcare -- that benefit from mold.

  • What products are produced using molds?



There are different types of cheese, like brie and blue cheese, where the growth of molds contributes to their smooth, creamy texture and a unique taste and aroma.

You can read Cheese and Mold: The Basics, from Proudly Cheese Wisconsin, to learn more.

Soy Foods

Soy sauce, miso, and tempeh are some of the foods where taste and texture are due to the fermentation process of molds.

Your Soy Sauce Probably Contains Mold - Here's Why That's a Good Thing, by Kelsey Ogletree for EatingWell, explains further.


Penicillin and other drugs were developed from molds.

If you are interested in how penicillin was accidentally discovered, check out our lesson under Additional Resources in the right-hand sidebar.

Whether they are helpful or harmful, molds are an important part of nature's cycle.

When you are ready to delve deeper into molds, move on to the Got It? section!

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