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21-1 The Kingdom Fungi
Photo Credit: ©D. Cavagnaro/DRK Photo
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What Are Fungi?
What Are Fungi?
Fungi are eukaryotic heterotrophs that have cell walls.
Their cell walls contain chitin, a complex carbohydrate also found in the exoskeletons of insects.
Fungi digest food outside their bodies and absorb it.
Some fungi absorb nutrients from decaying matter in soil.
Other fungi are parasites, absorbing nutrients from their hosts.
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3. Structure and Function of Fungi
Except for yeasts, all fungi are multicellular.
Fungi are made up of thin filaments called hyphae.
Each hypha is only one cell thick.
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4. Structure and Function of Fungi
In some fungi, cross walls divide hyphae into cells with 1 or 2 nuclei.
In the cross walls, there are openings through which the cytoplasm and nuclei can move.
Most fungi are made up of filaments called hyphae. In some fungi, the hyphae are divided by cross walls.
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5. Structure and Function of Fungi
Some hyphae lack cross walls and contain many nuclei.
Most fungi are made up of filaments called hyphae. In some fungi, the hyphae lack cross walls and contain many nuclei.
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6. Structure and Function of Fungi
Fungus Structure 
The bodies of multicellular fungi are composed of many hyphae tangled together into a thick mass called a mycelium.
The mycelium permits a large surface area to come in contact with the food source through which it grows.
A fruiting body is a reproductive structure growing from the mycelium in the soil beneath it.
A mushroom is the fruiting body of a fungus. Clusters of mushrooms are often part of the same mycelium, so they are part of the same organism.
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7. Structure and Function of Fungi
Fairy Rings
Mycelia can live for many years.
Through time, soil nutrients near the center of the mycelium become depleted.
Mushrooms will sprout only at the edges of the mycelium, producing a ring.
People once thought that fairies dancing in circles produced these rings so they were called “fairy rings.”
Over many years, fairy rings and grow to be meters in diameter.
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8. Structure and Function of Fungi
Structure of a Typical Fungus
Fruiting body
Hyphae
The body of a mushroom is part of a mycelium formed from many tangled hyphae. The major portion of the mycelium grows below ground. The visible portion of the mycelium is the reproductive structure, or fruiting body, of the mushroom.
Mycelium
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Reproduction in Fungi
Reproduction in Fungi
Most fungi reproduce both asexually and sexually.
Asexual reproduction occurs when hyphae break off and begin to grow on their own.
Some fungi produce spores, which scatter and grow. Spores are reproductive cells that are capable of growing into a new organism by mitosis alone.
In some fungi, spores are produced in structures called sporangia.
Sporangia are at tips of specialized hyphae called sporangiophores.
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Reproduction in Fungi
Sexual reproduction has two mating types: + and -
Because gametes of both mating types are about the same size, they are not called male and female.
Hyphae of opposite mating types meet and fuse, bringing “+” and “–” nuclei together in one cell.
After growth and development, the nuclei form a diploid zygote nucleus.
The zygote enters meiosis and produces haploid spores.
Spores are capable of growing into new organisms.
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How Fungi Spread
How Fungi Spread
Many fungi produce dry spores that scatter easily in the wind.
If these spores are to germinate, they must land in an environment with the proper combination of temperature, moisture, and food so they can grow.
Under the best circumstances, the probability that a spore will produce a mature organism is one in a billion.
Other fungi are specialized to lure animals, which disperse spores over long distances.
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