What are Fungi? - Types and Characteristics

What are Fungi? - Types and Characteristics
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  • 1:32 Fungi
  • 3:37 Mushrooms
  • 4:12 Mold
  • 4:51 Yeast
  • 6:44 Mycosis
  • 7:59 Lesson Summary
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Lesson Transcript
Instructor: Angela Hartsock

Angela has taught college Microbiology and has a doctoral degree in Microbiology.

In this lesson, we will examine the group of organisms known as the fungi. This group includes the familiar organisms mushrooms, yeasts and molds. We will look at several major characteristics of fungi, as well as a few disease-causing fungi.

Age of the Fungi

Ancient Earth had its fair share of dominant organisms. For most of the history of life, Earth has been dominated by the microscopic bacteria and archaea, floating, swimming and thriving in the ancient oceans that covered much of the globe. Through time, organisms got larger and more complex. There was a time when organisms resembling insects were dominant, then fish and reptiles. We've all heard of the dinosaurs ruling Earth, followed by mammals evolving. Now, humans are clearly the dominant organism. But, there was a time in history you have probably never heard of: the age of the fungus!

Around 250 million years ago, the earth was populated by ancient plants and animals. The Permian extinction changed all that. Over 90% of life on Earth vanished. The animals were decimated and so were the plants. This included many millions to billions of trees, leaving massive fields of dead wood. And, what thrives on dead wood and dead animal tissue? That's right, fungi. With few animals to tromp on them or eat them, few plants to crowd them and a massive dead wood buffet, the fungi after the Permian extinction were able to dominate the landscape. The little known, and even less heralded, golden age of the fungus had begun!

Fungi

Fungi, singular, fungus, is a group of eukaryotic, non-phototrophic organisms with rigid cell walls, that includes mushrooms, molds and yeasts. This definition has some words in it that probably need definitions of their own. Eukaryotic simply means that fungal cells have a nucleus, like plant and animal cells, which distinguishes them from the Bacteria and Archaea. Non-phototrophic means that they can't use light for energy because they lack chlorophyll, distinguishing them from plants. The cell walls of fungi are unique in that they contain large amounts of chitin, a structural component only found in the cell walls of fungi. The chitin makes the cells walls rigid.

So, if fungi can't perform photosynthesis, and I've never seen a mushroom hunting game on the savannah, what do they do for nutrients? Many fungi are saprophytes. A saprophyte is an organism that acquires nutrients from dead organic matter. This can be as common as seeing mushrooms growing on dead wood or mold surviving in your refrigerator on last week's takeout food. These fungi are actually very important to the health of the ecosystem, rapidly breaking down plant and animal material and returning it to a more usable form. Other fungi are parasites, obtaining nutrients from a host species. Many common plant diseases are a result of a fungus siphoning nutrition from the plant. There are even some human diseases caused by fungi, but we'll talk more in-depth about those later.

Many fungi are common contaminants of foods. Most fungi reproduce by releasing spores, which are the resistant, reproductive, resting stage of a fungus. These spores are able to survive the high temperatures and pH extremes often used for food preservation. Spores are also not killed by freezing and some can even germinate, resulting in actively growing fungi in your freezer! There are three major types of fungus: mushrooms, molds and yeasts. Let's take a quick look at each.

Mushrooms

To the average person, mushrooms are probably the best known fungi. Usually found springing up on dead wood after cool, wet weather, the mushroom is a common sight. Mushrooms generally consist of a stalk with a large cap on top. This cap produces the spores that the mushroom releases in order to reproduce and colonize new environments. Many species of mushrooms are edible and delicious, but others can be very toxic. Since knowing the difference can take a very experienced eye, eating wild mushrooms is usually not a fantastic idea for the average person.

Mold

Like mushrooms, molds are very recognizable. Forget about that brick of cheddar cheese for too long and suddenly it's covered with green fuzz. That fuzz is why molds are often called filamentous fungi, and the filaments give it that fuzzy or fluffy appearance. Hyphae is a technical term for the long, branching mold filaments. Specialized hyphae, called conidia, are often pigmented and reach up above the surface of the food source. These conidia are responsible for producing and releasing the mold spores for reproduction and dispersal. The common and ubiquitous bread mold is in the genus Rhizopus.

Yeasts

To a microbiologist, yeasts are the most important fungi, so I'll spend a little more time here. Yeast is the common term for any unicellular fungus. The mushrooms and molds are all multicellular organisms, but yeasts usually exist as only a single cell. The cell is larger than a bacterial cell and contains a nucleus and other organelles. Yeasts reproduce by budding. The new offspring cell begins as a small outgrowth on the membrane of the parent cell, which gets larger before eventually pinching off. This process is asexual, resulting in two clones. Some yeast can reproduce sexually by simply fusing and creating a genetically recombined zygote cell. The zygote contains DNA from both parents.

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