Fungi
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C HAPTER
Chapter 1. Fungi
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Fungi
Introduction
Look at the gray fuzz growing on the bread in the figure below. It’s a type of fungus. It looks gross and it spoils
the bread. But fungi like this actually play important roles in many ecosystems. There are also many human uses of
fungi, which you’ll learn when you read this lesson.
FIGURE 1.1
The fuzzy growth on this bread is a fungus.
What Are Fungi?
Fungi (fungus, singular) are relatively simple eukaryotic organisms. They are placed in their own kingdom, the
Fungus Kingdom. Most fungi are multicellular organisms. These fungi are called molds. However, some fungi
exist as single cells. These fungi are called yeasts. You can see examples of different types of fungi in the figure
below. For a funny, fast-paced overview of fungi, watch this video:
http://www.youtube.com/watch?v=m4DUZhnNo4s
Classification and Evolution of Fungi
For a long time, scientists classified fungi as members of the Plant Kingdom. Fungi share several obvious traits with
plants. For example, both fungi and plants lack the ability to move. Both grow in soil, and both have cell walls.
Some fungi even look like plants.
Fungi Classification
Today, fungi are no longer classified as plants. We now know that they have important traits that set them apart from
plants. That’s why they are placed in their own kingdom. How do fungi differ from plants?
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FIGURE 1.2
Examples of fungi
• The cell walls of fungi are made of chitin. Chitin is a tough carbohydrate that also makes up the outer skeleton
of insects. The cell walls of plants are made of cellulose.
• Fungi are heterotrophs that absorb food from other organisms. Plants are autotrophs that make their own food.
The Fungus Kingdom is large and diverse. It may contain more than a million species. However, fewer than 100,000
species of fungi have been identified.
Fungi Evolution
The earliest fungi evolved about 600 million years ago. They lived in the water. Fungi colonized the land around
the same time as plants. That was probably between 400 and 500 million years ago. After that, fungi became very
abundant on land. By 250 million years ago, they may have been the dominant life forms on land.
Structure of Fungi
Yeasts grow as single cells. Other fungi grow into multicellular, thread-like structures. These structures are called
hyphae (hypha, singular). You can see a photo of hyphae in the figure below. They resemble plant roots. Each
hypha consists of a group of cells surrounded by a tubular cell wall.
A mass of hyphae make up the body of a fungus. The body is called the mycelium (mycelia, plural). A mycelium
may range in size from microscopic to very large. In fact, the largest living thing on Earth is the mycelium of a
single fungus. Nicknamed the “humongous fungus,” it grows in a forest in Oregon. A small part of the fungus is
pictured in the figure below. The giant fungus covers an area of 2384 acres. That’s about the size of 1,665 football
fields! The fungus is estimated to be at least 2400 years old, but it could be much older.
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Chapter 1. Fungi
FIGURE 1.3
White hyphae of a fungus
FIGURE 1.4
These mushrooms are a visible part of the
humongous fungus in Oregon. Most of
the fungus is underground in the soil. It
spreads by sending out hyphae into the
surrounding soil.
Fungi Reproduction
Most fungi reproduce both asexually and sexually. Asexual reproduction is by haploid spores (special cells for
reproducing). Yeast reproduce by haploid spores or budding.
Roles of Fungi in Ecosystems
Most fungi grow on moist soil or rotting vegetation such as dead logs. Some fungi live in water. Others live in or
on other organisms. Fungi get their nutrition by absorbing organic compounds from other organisms. The other
organisms may be dead or alive, depending on the fungus.
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Fungi as Decomposers
Most fungi get organic compounds from dead organisms. Fungi use their hyphae to penetrate deep into decaying
organic matter. They produce enzymes at the tips of their hyphae. The enzymes digest the organic matter so the
fungal cells can absorb it. Fungi are the main decomposers in forests. They are the only decomposers that can break
down cellulose and wood. They have special enzymes for this purpose.
Fungi Symbiosis
Many fungi get organic compounds from living organisms. They have close relationships with other species. A
close relationship between two species is called a symbiotic relationship. Two symbiotic relationships in fungi are
mycorrhiza and lichen. These relationships are beneficial for both species.
• Mycorrhiza is a relationship between a fungus and a plant. The fungus grows in or on the plant’s roots. The
fungus benefits from easy access to food made by the plant. The plant benefits because the fungal hyphae
absorb water and nutrients from the soil that the plant needs.
• Lichen is a relationship between a fungus and cyanobacteria or green algae. The fungus grows around the
bacterial or algal cells. The fungus benefits by getting some of the food made by the photosynthetic cells. The
bacteria or algae benefit by getting some of the water and nutrients absorbed by the fungus. You can see a
picture of lichen in Figure 1.5.
FIGURE 1.5
Lichen growing on a rock
Some fungi have a different kind of relationship with plants. They are plant parasites. They get food from the
plants and cause harm to the plants in return. Fungi are the major causes of disease in agricultural crops. They may
eventually kill their plant hosts.
Some fungi are animal parasites. The wasp in Figure 1.6 is infected with a fungus. The fungus is the white fuzzy
matter on the dark brown moth.
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Chapter 1. Fungi
FIGURE 1.6
Wasp infected by a parasitic white fungus
Fungi and People
Fungi may cause disease in people as well as other organisms. On the other hand, people have been using fungi for
thousands of years.
Human Uses of Fungi
One way we use fungi is by eating them. Many species of mushrooms are edible. Yeasts are used for break making.
Other fungi are used to ferment foods, such as soy sauce and cheeses. You can see the fungus growing through the
blue cheese in Figure 1.7. The fungus gives the cheese its distinctive appearance and taste.
FIGURE 1.7
Blue cheese is blue because of the fungus
growing throughout it.
People also use fungi:
•
•
•
•
to produce antibiotics.
to produce human hormones such as insulin.
as natural pesticides.
as model research organisms.
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Fungi and Human Diseases
Several common human diseases are caused by fungi. They include ringworm and athlete’s foot, both shown in
Figure 1.8. Ringworm isn’t caused by a worm. It’s a skin infection by a fungus that leads to a ring-shaped rash. The
rash may occur on the head, neck, trunk, arms, or legs. Athlete’s foot is caused by the same fungus as ringworm.
But in athlete’s foot, the fungus infects the skin between the toes. Athlete’s foot is the second most common skin
disease in the U.S.
FIGURE 1.8
Ringworm (left) and athlete’s foot (right)
are fungal infections of the skin.
Lesson Summary
• Fungi are eukaryotes in the Fungus Kingdom. Fungi include molds, which are multicellular, and yeasts, which
are single-celled.
• Fungi are similar in some ways to plants but have unique traits that set them apart from plants. Fungi first
evolved about 600 million years ago.
• Most fungi grow into multicellular threadlike hyphae. A mass of hyphae makes up the body, or mycelium, of
the fungus.
• Most fungi reproduce both asexually and sexually. Asexual reproduction is by haploid spores (or by budding
in yeasts). Sexual reproduction is by diploid spores.
• Most fungi are decomposers. They are the main decomposers in forests. Many fungi have symbiotic relationships with other species.
• People use fungi for food and other purposes. Some fungi cause human diseases.
Lesson Vocabulary
•
•
•
•
•
•
•
•
•
•
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chitin
fungus (fungi, plural)
Fungus Kingdom
hypha (hyphae, plural)
lichen
mold
mycelium (mycelia, plural)
mycorrhiza
spore
yeast
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Chapter 1. Fungi
Lesson Review Questions
Recall
1.
2.
3.
4.
What are fungi? What are two examples of fungi?
Describe the hyphae and mycelium of a fungus.
Give an overview of fungi reproduction.
What are some ways that people use fungi?
Apply Concepts
5. Assume that you notice fungi growing on a wooden fence in your backyard. You want the fence to last as long
as possible. Should you remove the fungi or leave them alone? Explain your answer.
Think Critically
6. Fungi used to be placed in the Plant Kingdom. Explain why they are now placed in their own kingdom.
7. Compare and contrast mycorrhiza and lichen.
Points to Consider
Fungi share certain traits with plants.
• How do plants differ from fungi?
• What are some other traits of plants?
References
1. User:Ciar/Wikimedia Commons. http://commons.wikimedia.org/wiki/File:Moldy_old_bread.JPG . Public
Domain
2. Mushroom: Tony Wills; Toothed fungus: Moonlight0551; Yeast: BCarver1; Puffball: Jason Hollinger. Exam
ples of fungi . Mushroom: CC BY 2.5; Toothed fungus: CC BY 2.0; Yeast: Public Domain; Puffball: CC BY
2.0
3. Lex vB. White hyphae of a fungus . Public Domain
4. USDA. Mushrooms from a giant fungus . Public Domain
5. User:Hardyplants/Wikipedia. Lichen growing on a rock . Public Domain
6. Image copyright Dr. Morley Read, 2014. Wasp infected by a parasitic white fungus . Used under license
from Shutterstock.com
7. Stuart Webster. Blue cheese is blue because of the fungus growing throughoutit. . CC BY 2.0
8. Ringworm: Dr. Lucille K. Georg/Centers for Disease Control and Prevention; Athlete’s foot: User:Falloonb/Wikipedia.
Ringworm and athlete’s foot are fungal infections of the skin. . Public Domain
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