The Kingdom Fungi

1
The Kingdom Fungi

• These morels are a type of fungus prized by many
  people for their distinctive flavor
• Unlike the violets, fungi are not plants and do
  not produce their own food

2
The Kingdom Fungi
3
The Kingdom Fungi

• In spring, if you know where to look, you can
  find one of the most prized of all foodsthe
  common morelgrowing wild in woodlands throughout
  the United States
• Its ridged cap is often camouflaged by dead
  leaves that collect in abandoned orchards or
  underneath old oaks or tulip poplars
• Some morels grow alone, but others grow in groups
• They appear suddenly, often overnight, and live
  for only a few days
• What are these mysterious organisms?
• How do they grow so quickly?

4
KINGDOM FUNGI

• Diverse group of over 65,000 species
• Most fungi are saprophytic or parasitic, and a
  few are predatory
• Saprophyte
• Is an organism that feeds on dead organic matter
• Recycling the nutrients
• Referred to as decomposers
• Without decomposers, nutrients would not be
  reused and life could not continue on earth
• Parasite
• Derives its nutrients from a living host organism
  at the hosts expense
• Cause many plant and animal diseases
• Predatory
• Captures prey for food
• Example Pleurotus ostreatus capture roundworms

5
What Are Fungi?

• Like mushrooms and molds, morels are fungi
• The way in which many fungi grow from the ground
  once led scientists to classify them as
  nonphotosynthetic plants
• But they aren't plants at all
• In fact, fungi are very different from plants

6
What Are Fungi?

• Fungi are eukaryotic heterotrophs that have cell
  walls
• The cell walls of fungi are made up of chitin, a
  complex carbohydrate that is also found in the
  external skeletons of insects
• Recall that heterotrophs depend on other
  organisms for food
• Unlike animals, fungi do not ingest their food
• Instead, they digest food outside of their bodies
  and then absorb it
• Many fungi feed by absorbing nutrients from
  decaying matter in the soil
• Others live as parasites, absorbing nutrients
  from the bodies of their hosts

7
FUNGAL EVOLUTION

• Precambrian fossils about 900 million years old
• Late Carboniferous period, fossils indicate that
  all modern divisions of fungi had evolved
• Most are terrestrial
• Indicates adaptive radiation shortly after plants
  and animals colonized the land
• Like all eukaryotes, arose from prokaryotes
• Arose from other heterotrophs
• Present theory is that they evolved from red algae

8
Structure and Function of Fungi

• Except for yeasts, all fungi are multicellular
• Multicellular fungi are composed of thin
  filaments called hyphae (singular hypha)
• Each hypha is only one cell thick
• In some fungi, cross walls divide the hyphae into
  cells containing one or two nuclei
• In the cross walls, there are tiny openings
  through which the cytoplasm and nuclei can move
• Other hyphae lack cross walls and contain many
  nuclei

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CHARACTERISTICS

• Hypha vegetative filament of the fungus
• Types
• Septate
• Filaments with internal cross walls (septum)
• Individual cells have nuclei
• Coenocytic
• Filaments without internal cross walls (septum)
• Filament contains many nuclei that move through
  the cytoplasm
• Grows at the tip where new membrane material is
  added by the action of Golgi bodies
• A mat of interwoven hyphae is called mycelium
• Cell wall composed of chitin (not cellulose)
• Complex polysaccharide also found in the
  exoskeleton of insects and other invertebrates
• Store food as glycogen (like animals)
• Reproduce asexually (spores)(fragmentation) and
  sexually (gametes)
• Heterokaryotic hypha genetically different
  nuclei coexist within a hypha
• Homokaryotic hypha genetically similar nuclei
  coexist within a hypha

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STRUCTURE OF FUNGI
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Structure of Two Types of Hyphae  

• Fungi are eukaryotes that have cell walls made of
  chitin
• Most fungi are made up of filaments called hyphae
• In some fungi, the hyphae are divided by cross
  walls
• These cells may contain one or two nuclei
• In other fungi, the hyphae lack cross walls and
  contain many nuclei

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Structure of Two Types of Hyphae  
13
HYPHAE TYPES
14
STRUCTURE OF FUNGI
15
Fungus Structure 

• The bodies of multicellular fungi are composed of
  many hyphae tangled together into a thick mass
  called a mycelium
• The mycelium (plural mycelia) is well suited to
  absorb food because it permits a large surface
  area to come in contact with the food source
  through which it grows

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Structure of a Multicellular Fungus  

• 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

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Structure of a Multicellular Fungus  
18
Fungus Structure

• What you recognize as a mushroom is actually the
  fruiting body of a fungus
• A fruiting body is a reproductive structure
  growing from the mycelium in the soil beneath it
• Clusters of mushrooms are often part of the same
  mycelium, which means that they are part of the
  same organism

19
Fairy Rings 

• Some mycelia can live for many years
• As time goes by, soil nutrients near the center
  of the mycelium become depleted
• As a result, new mushrooms sprout only at the
  edges of the mycelium, producing a ring
• People once thought fairies dancing in circles
  during warm nights produced these rings, so they
  were called fairy rings
• Over many years, fairy rings can become
  enormousfrom 10 to 30 meters in diameter

20
Reproduction in Fungi

• Most fungi reproduce both asexually and sexually
• Asexual reproduction takes place when cells or
  hyphae break off from a fungus and begin to grow
  on their own
• Some fungi also produce spores, which can scatter
  and grow into new organisms
• Recall that a spore is a reproductive cell that
  is capable of growing into a new organism by
  mitosis alone
• In some fungi, spores are produced in structures
  called sporangia (singular sporangium)
• Sporangia are found at the tips of specialized
  hyphae called sporangiophores

21
Reproduction in Fungi

• Sexual reproduction in fungi usually involves two
  different mating types
• Because gametes of both mating types are about
  the same size, they are not called male and
  female
• Rather, one mating type is called (plus) and
  the other - (minus)

22
Reproduction in Fungi

• When hyphae of opposite mating types meet, they
  start the process of sexual reproduction by
  fusing, bringing plus and minus nuclei together
  in the same cell
• After a period of growth and development, these
  nuclei form a diploid zygote nucleus
• In most fungi, the diploid zygote then enters
  meiosis, completing the sexual phase of its life
  cycle by producing haploid spores
• Like the spores produced asexually, these spores
  are also capable of growing, by repeated rounds
  of mitosis, into new organisms

23
How Fungi Spread

• Fungal spores are found in almost every
  environment
• This is why molds seem to spring up in any
  location that has the right combination of
  moisture and food
• Many fungi produce dry, almost weightless spores
• These spores scatter easily in the wind
• On a clear day, a few liters of fresh air may
  contain hundreds of spores from many species of
  fungi

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How Fungi Spread

• If these spores are to germinate, they must land
  in a favorable environment
• There must be the proper combination of
  temperature, moisture, and food so that the
  spores can grow
• Even under the best of circumstances, the
  probability that a spore will produce a mature
  organism can be less than one in a billion

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How Fungi Spread

• Other fungi are specialized to lure animals,
  which disperse fungal spores over long distances
• Stinkhorns smell like rotting meat, which
  attracts flies
• When they land on the stinkhorn, the flies ingest
  the sticky, smelly fluid on the surface of the
  fungus
• The spore-containing fluid will pass unharmed out
  of the flies' digestive systems, depositing
  spores over many kilometers

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FUNGI CLASSIFICATION

• Four Divisions
• Based primarily on the structure of hyphae or on
  the type of reproduction

27
Classification of Fungi

• The kingdom Fungi has over 100,000 species
• Fungi are classified according to their structure
  and method of reproduction
• The methods by which fungi reproduce are unlike
  those of any other kingdom
• The four main groups of fungi are
• Common molds (Zygomycota)
• Sac fungi (Ascomycota)
• Club fungi (Basidiomycota)
• Imperfect fungi (Deuteromycota)

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CLASSIFICATION OF FUNGI
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The Common Molds

• The familiar molds that grow on meat, cheese, and
  bread are members of the phylum Zygomycota, also
  called zygomycetes
• Zygomycetes have life cycles that include a
  zygospore
• A zygospore is a resting spore that contains
  zygotes formed during the sexual phase of the
  mold's life cycle
• The hyphae of zygomycetes generally lack cross
  walls, although the cells of their reproductive
  structures do have cross walls

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DIVISION ZYGOMYCOTA

• Approximately 600 species
• Mostly terrestrial organisms
• Commonly found in soil and dung
• Coenocytic hyphae
• Example Rhizopus Stolonifer
• Bread mold
• Three different types of hyphae
• Rhizoids
• Anchoring hyphae that penetrate the bread
• Produce digestive enzymes, and absorb nutrients
• Stolons
• Hyphae that grow across the surface of the bread
• Sporangiophores
• Upright hyphae that produce sporangia at their
  tips which produce spores

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Structure and Function of Bread Mold 

• Black bread mold, Rhizopus stolonifer, is a
  familiar zygomycete
• Expose preservative-free bread to dust, and you
  can grow the mold
• Keep the bread warm and moist in a covered jar,
  and in a few days dark fuzz will appear
• With a hand lens, you can see delicate hyphae on
  moldy bread
• There are two different kinds of hyphae
• The rootlike hyphae that penetrate the bread's
  surface are rhizoids
• Rhizoids anchor the fungus to the bread, release
  digestive enzymes, and absorb digested organic
  material
• The stemlike hyphae that run along the surface of
  the bread are stolons
• The hyphae that push up into the air are the
  sporangiophores, which form sporangia at their
  tips
• A single sporangium may contain up to 40,000
  spores

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Life Cycle of Molds 

• The life cycle of black bread mold is shown in
  the figure
• Its sexual phase begins when hyphae from
  different mating types fuse to produce
  gamete-forming structures known as gametangia (
  singular gametangium)
• Haploid (N) gametes produced in the gametangia
  fuse with gametes of the opposite mating type to
  form diploid (2N) zygotes
• These zygotes develop into thick-walled
  zygospores, which may remain dormant for months
• When conditions become favorable, the zygospore
  germinates, then undergoes meiosis, and new
  haploid spores are released
• The significance of this sexual processzygote
  formation followed by meiosisis that it produces
  new combinations of genetic information that may
  help the organism meet changing environmental
  conditions

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ZYGOMYCOTARHIZOPUS STOLONIFER
34
Life Cycle of a Black Bread Mold

• Zygomycetes have life cycles that include a
  zygospore
• During sexual reproduction in the bread mold
  Rhizopus stolonifer, hyphae from two different
  mating types form gametangia
• The gametangia fuse, and zygotes form within
  zygospore
• The zygospore develops a thick wall and can
  remain dormant for long periods
• The zygospore eventually germinates, and a
  sporangium emerges
• The sporangium reproduces asexually by releasing
  haploid spores produced by meiosis

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Life Cycle of a Black Bread Mold
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DIVISION ZYGOMYCOTAASEXUAL REPRODUCTION

• Hormonal action causes upright sporangiophores to
  form
• Sporangia form at the tips of sporangiophores
  producing spores (sporangiospores) that are
  dispersed by the wind

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SEXUAL AND ASEXUALREPRODUCTIONOF ZYGOMYCOTA
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ZYGOMYCOTALIFE CYCLE
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DIVISION ZYGOMYCOTASEXUAL REPRODUCTION

• Called Conjugation
• Two filaments line up next to each other
• Hyphae of two mating strains come close together
• Each hyphae encloses haploid (1N) nuclei
• Hormones cause short branches to form on each
  hypha and grow outward until they touch
• Septa form near the tip of each branch
• Resulting cell is a gametangium (1N) that
  contains several nuclei
• Gametangia fuse then nuclei fuse in pairs (2N)
• Each pair contains one nucleus from each mating
  strain (2N)
• Zygote contains many diploid (2N) nuclei
• Wall surrounding the zygote (2N) thickens forming
  a protective, temporary structure called a
  zygospore (2N)
• Meiosis occurs when the zygospore germinates
  forming new hyphae (1N)

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SEXUAL AND ASEXUALREPRODUCTIONOF ZYGOMYCOTA
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ZYGOMYCOTALIFE CYCLE
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ZYGOMYCOTASEXUAL REPRODUCTIONCONJUGATION
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ZYGOTE
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DIVISION ZYGOMYCOTAASEXUAL/SEXUAL REPRODUCTION

• Provide adaptive advantages
• Asexual Reproduction
• During periods when the environment is favorable
• Rapid formation of spores ensures the quick
  spread of the species
• Sexual Reproduction
• In periods of environmental stress
• Ensures genetic recombination before the hyphae
  die

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The Sac Fungi

• Sac fungi, also known as ascomycetes, belong to
  the phylum Ascomycota
• The phylum Ascomycota is named for the ascus, a
  reproductive structure that contains spores
• There are more than 30,000 species of
  ascomycetes, making it the largest phylum of the
  kingdom Fungi
• Some ascomycetes, such as the cup fungi, are
  large enough to be visible when they grow above
  the ground
• Others, such as yeasts, are microscopic

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DIVISION ASCOMYCOTA

• Sac fungi
• Approximately 30,000 species
• Largest Division of Fungi
• Live in a variety of habitats, including
  freshwater and saltwater
• Morels, powdery mildews, yeast, and cup fungi

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ASCOMYCETEEDIBLE MOREL
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Life Cycle of Sac Fungi 

• The life cycle of an ascomycete usually includes
  both asexual and sexual reproduction
• The life cycle of a cup fungus is shown in the
  figure at right

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Life Cycle of an Ascomycete

• The life cycle of ascomycetes includes both
  asexual and sexual reproduction
• During asexual reproduction, spores called
  conidia are formed at the tips of specialized
  hyphae called conidiophores
• During sexual reproduction, hyphae of two mating
  types fuse to form hyphae with two haploid
  (monoploid) nuclei (N N)
• The N N hyphae then form a fruiting body, which
  eventually releases ascospores
• Ascomycetes are named for the ascus, the
  reproductive structure that contains ascospores

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Life Cycle of an Ascomycete
51
Life Cycle of Sac Fungi 

• In asexual reproduction, tiny spores called
  conidia (singular conidium) are formed at the
  tips of specialized hyphae called conidiophores
• These spores get their name from the Greek word
  konis, which means dust
• If a conidium lands in a suitable environment, it
  grows into a haploid mycelium

52
Life Cycle of Sac Fungi 

• Sexual reproduction occurs when the haploid
  hyphae of two different mating types ( and -)
  grow close together
• The N N hyphae then produce a fruiting body in
  which sexual reproduction continues
• Gametangia from the two mating types fuse, but
  the haploid (N) nuclei do not fuse
• Instead, this fusion produces hyphae that contain
  haploid nuclei from each of the mating types (N
  N)

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Life Cycle of Sac Fungi 

• The ascus (plural asci) forms within the
  fruiting body
• Within the ascus, two nuclei of different mating
  types fuse to form a diploid zygote (2N)
• The zygote soon divides by meiosis, producing
  four haploid cells
• In most ascomycetes, meiosis is followed by a
  cycle of mitosis, so that eight cells known as
  ascospores are produced
• In a favorable environment, an ascospore can
  germinate and grow into a haploid mycelium

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DIVISION ASCOMYCOTA

• Sexual Reproduction
• Hyphae of the Ascogonium (female gametangium)
  fuses with the Antheridium (male gametangium)
• Gametangia fuse, and male nuclei move into the
  ascogonium
• Male and female nuclei pair but do not fuse
• Cell divide forming heterokaryotic hyphae that
  intertwine forming an ascocarp
• Reproductive body of an ascomycete
• Sacs called asci form on the surface
• Each ascus encloses two nuclei
• Nuclei fuse
• Diploid nucleus undergoes meiosis producing four
  haploid nuclei followed by a mitotic division
  resulting in 8 haploid ascospores
• Ascus ruptures releasing ascospores into the air
• Ascospores germinate into new hyphae on the ground

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ASCOMYCOTA

• Asexual Reproduction
• Produces spores called conidium
• Conidia form on the ends of specialized branches
  called conidiophores

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ASCOMYCETE REPRODUCTION
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ASCOMYCOTA LIFE CYCLE
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Yeasts

• Yeasts are unicellular fungi
• The yeasts used by humans for baking and brewing
  are classified as ascomycetes because they form
  asci with ascospores during the sexual phase of
  their life cycle

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Yeasts

• You might think of yeast as a lifeless, dry
  powder that is used to make bread
• Actually, the dry granules contain ascospores,
  which become active in a moist environment
• To see this for yourself, add a spoonful of dry
  yeast to half a cup of warm water that contains
  some sugar
• In about 20 minutes, when you examine a drop of
  this mixture under a microscope, you will be able
  to see cell division in the rapidly growing yeast
  cells
• The process of asexual reproduction you are
  observing is called budding

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Yeasts

• The common yeasts used for baking and brewing are
  members of the genus Saccharomyces, which means
  sugar fungi
• These yeasts are grown in a rich nutrient mixture
  containing very little oxygen
• Prior to baking, the nutrient mixture is a mound
  of thick dough
• Lacking oxygen, the yeasts within the mixture use
  the process of alcoholic fermentation to obtain
  energy
• The byproducts of alcoholic fermentation are
  carbon dioxide and alcohol
• The carbon dioxide gas makes beverages bubble and
  bread rise (by producing bubbles within the
  dough)
• The alcohol in bread dough evaporates during
  baking
• In brewing, alcohol remains in the resulting
  alcoholic beverages

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DIVISION ASCOMYCOTA

• Yeast unicellular
• Asexual Reproduction budding
• Sexual Reproduction formation of a zygote by the
  fusion of two ascospores
• 600 species
• Saccharomyces cerevisiae used in brewing
  processes
• Ability to breakdown carbohydrates forming ethyl
  alcohol and carbon dioxide gas makes yeast useful
  in industry
• Baking and brewing

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The Club Fungi

• The phylum Basidiomycota, or club fungi, gets its
  name from a specialized reproductive structure
  that resembles a club
• The spore-bearing structure is called the
  basidium (plural basidia)
• Basidia are found on the gills that grow on the
  underside of mushroom caps

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DIVISION BASIDIOMYCOTA

• Approximately 25,000 species
• Called club fungi
• Examples mushrooms, toadstools, puffballs,
  rusts, and smuts

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DIVISION BASIDIOMYCOTA

• Basidiocarp mushroom
• Reproductive body of a basidiomycete
• Formed when underground hyphae grow upward and
  intertwine
• Cap (fruiting body) is attached to a stalk (stem)
• Underside are radiating rows of gills which
  contain specialized club-shaped reproductive
  cells called basidia
• In each basidium two nuclei become isolated by a
  complete septum
• Nuclei fuse and form a diploid zygote
• Meiosis then results in four nuclei that are
  pushed into cytoplasmic extensions to form
  basidiospores
• At maturity, the basidiospores are released and
  germinate into new homokaryotic hyphae
• As the homokaryotic hyphae grow, septa form so
  that each cell contains one nucleus
• These homokaryotic, septate hyphae are called the
  primary mycelium
• Primary hyphae grow and fuse with hyphae from
  another mating strain resulting in the formation
  of secondary hyphae
• Hyphae of these mycelium are heterokaryotic,
  containing one nucleus from each mating strain in
  each cell
• Secondary mycelium intertwines and forms a
  basiocarp

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Life Cycle of Club Fungi 

• Basidiomycetes undergo what is probably the most
  elaborate life cycle of all the fungi
• As shown in the figure at right, a basidiospore
  germinates to produce a haploid primary mycelium,
  which begins to grow
• Before long, the mycelia of different mating
  types fuse to produce a secondary mycelium
• The cells of the secondary mycelium contain
  haploid nuclei of each mating type
• Secondary mycelia may grow in the soil for years,
  reaching an enormous size
• A few mycelia have been found to be hundreds of
  meters across, making them perhaps the largest
  organisms in the world

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Life Cycle of a Basidiomycete

• The club fungi are named after the club shape of
  their reproductive structure, the basidium
• The cap of a basidiomycete such as a mushroom is
  composed of tightly packed hyphae
• The lower side of the cap is composed of
  gillsthin blades of tissue lined with basidia
  that produces basidiospores

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Life Cycle of a Basidiomycete
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BASIDIOMYCETE REPRODUCTION
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BASIDIOMYCETE REPRODUCTION
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BASIDIOMYCOTALIFE CYCLE
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FRUITING BODYBASIDIOCARP
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FRUITING BODY BASIDIOCARP
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FRUITING BODY BASIDIOCARP
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FRUITING BODY BASIDIOCARP
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FRUITING BODY BASIDIOCARP
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PUFFBALL OFBASIDIOMYCETES
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Life Cycle of Club Fungi 

• When the right combination of moisture and
  nutrients occurs, spore-producing fruiting bodies
  push above the ground
• You would recognize these fruiting bodies as
  mushrooms
• Each mushroom begins as a mass of growing hyphae
  that forms a button, or thick bulge, at the
  soil's surface

78
Life Cycle of Club Fungi 

• Fruiting bodies expand with astonishing speed,
  sometimes producing fully developed mushrooms
  overnight
• This remarkable growth rate is caused by cell
  enlargement, not cell division
• The cells of the hyphae enlarge by rapidly taking
  in water

79
Life Cycle of Club Fungi 

• When the mushroom cap opens, it exposes hundreds
  of tiny gills on its underside
• Each gill is lined with basidia
• The two nuclei in each basidium fuse to form a
  diploid (2N) zygote cell, which then undergoes
  meiosis, forming clusters of haploid
  basidiospores
• The basidiospores form at the edge of each
  basidium and, within a few hours, are ready to be
  scattered
• Mushrooms are truly amazing reproductive
  structuresa single mushroom can produce billions
  of spores, and giant puffballs can produce
  trillions

80
Diversity of Club Fungi 

• In addition to mushrooms, basidiomycetes include
  shelf fungi, which grow near the surfaces of dead
  or decaying trees
• The visible bracketlike structure that forms is a
  reproductive structure, and it, too, is a
  prolific producer of spores
• Puffballs, earthstars, jelly fungi, and plant
  parasites known as rusts are other examples of
  basidiomycetes

81
Edible and Inedible Mushrooms 

• Many types of fungi have long been considered
  delicacies, and several different species of
  mushrooms are cultivated for food
• You may have already tasted sliced mushrooms on
  pizza, feasted on delicious sautéed portobello
  mushrooms, or eaten shiitake mushrooms
• When properly cooked and prepared, domestic
  mushrooms are tasty and nutritious

82
FUNGI IN INDUSTRY
83
Edible and Inedible Mushrooms 

• Wild mushrooms are a different story Although
  some are edible, many are poisonous
• Because many species of poisonous mushrooms look
  almost identical to edible mushrooms, you should
  never pick or eat any mushrooms found in the wild
• Instead, mushroom gathering should be left to
  experts who can positively identify each mushroom
  they collect
• The result of eating a poisonous mushroom can be
  severe illness, or even death

84
The Imperfect Fungi

• Fungi are usually classified by the sexual phase
  of their life cycle
• So, what do biologists do when they discover a
  fungus that does not seem to have a sexual phase?
• Until a sexual phase is discovered, scientists
  place it in the phylum called Deuteromycota, or
  the imperfect fungi
• The term imperfect, by the way, doesnt mean that
  theres anything wrong with these organisms
• It simply means that our understanding of their
  life cycles may not be perfect
• The Deuteromycota are fungi that cannot be placed
  in other phyla because researchers have never
  been able to observe a sexual phase in their life
  cycles
• A majority of the imperfect fungi closely
  resemble ascomycetes
• Others are similar to basidiomycetes, and a few
  resemble the zygomycetes

85
The Imperfect Fungi

• One of the best-known genera of the imperfect
  fungi is Penicillium
• The species Penicillium notatum is a mold that
  frequently grows on fruit and is the source of
  the antibiotic penicillin
• Like the ascomycetes, Penicillium reproduces
  asexually by means of conidia, leading many
  biologists to conclude that Penicillium evolved
  from an ascomycete that lost the sexual phase of
  its life cycle

86
DIVISION DEUTEROMYCOTA

• Sometimes called the imperfect fungi or, Fungi
  Imperfecti
• 10,000 species
• Classification based on type of asexual
  reproduction
• No sexual reproductive phase discovered
• Placed in this Division until a sexual phase, if
  it exist, is identified
• Some forms cause ringworm and athletes foot
• Aspergillus used to ferment soy beans in the
  production of soy sauce

87
 Ecology of Fungi

• Fungi have been around since life first moved
  onto land
• In fact, the oldest known fossils of fungi were
  formed about 460 million years ago
• At that time, the largest land plants were small
  organisms similar to mosses
• Paleontologists think that fungi helped early
  plants to obtain nutrients from the ground
• Their early appearance suggests that fungi may
  have been essential to plants' successful
  colonization of the land, one of the key events
  in the history of life

88
 Ecology of Fungi

• Over time, fungi have become an important part of
  virtually all ecosystems, adapting to conditions
  in every corner of Earth
• Because most fungi live their lives out of our
  sight, people often overlook them
• But without fungi, the world would be a very
  different place

89
All Fungi Are Heterotrophs

• As heterotrophs, fungi cannot manufacture their
  own food
• Instead, they must rely on other organisms for
  their energy
• Unlike animals, fungi cannot move to capture
  food, but their mycelia can grow very rapidly
  into the tissues and cells of plants and other
  organisms
• Many fungi are saprobes, organisms that obtain
  food from decaying organic matter
• Others are parasites, which harm other organisms
  while living directly on or within them
• Still other fungi are symbionts that live in
  close and mutually beneficial association with
  other species

90
All Fungi Are Heterotrophs

• Although most fungi feed on decaying matter, a
  few feed by capturing live animals
• Pleurotus ostreatus is a carnivorous fungus that
  lives on the sides of trees
• As roundworms crawl into the fungus to feed, they
  are exposed to a fungal chemical that makes them
  become sluggish
• As the worms slow to a stop, fungal hyphae
  penetrate their bodies, trapping them in place
  and then digesting them

91
Fungi as Decomposers

• Fungi play an essential role in maintaining
  equilibrium in nearly every ecosystem, where they
  recycle nutrients by breaking down the bodies and
  wastes of other organisms
• Many fungi feed by releasing digestive enzymes
  that break down leaves, fruit, and other organic
  material into simple molecules
• These molecules then diffuse into the fungus
• The mycelia of fungi produce digestive enzymes
  that speed the breakdown of wastes and dead
  organisms
• In so doing, they promote the recycling of
  nutrients and essential chemicals, helping to
  maintain ecosystem equilibrium

92
Fungi as Decomposers

• Imagine a world without decomposers
• Without decay, the energy-rich compounds that
  organisms accumulate during their lifetimes would
  be lost forever
• Many organisms, especially plants, remove
  important trace elements and nutrients from the
  soil
• If these materials were not returned, the soil
  would quickly be depleted, and Earth would become
  lifeless and barren

93
Fungi as Parasites

• As useful as many fungi are, others can infect
  both animals and plants, disrupting their
  internal equilibrium and causing disease
• Parasitic fungi cause serious plant and animal
  diseases
• A few cause diseases in humans

94
Plant Diseases 

• Fungi cause diseases such as corn smut, which
  destroys corn kernels
• Mildews, which infect a wide variety of fruits,
  are also fungi
• Fungal diseases are responsible for the loss of
  approximately 15 percent of the crops grown in
  temperate regions of the world
• In tropical areas, where high humidity favors
  fungal growth, the loss of crops is sometimes as
  high as 50 percent
• Fungi are in direct competition with humans for
  food
• Unfortunately for us, sometimes fungi win that
  competition

95
Plant Diseases 

• One fungal diseasewheat rustaffects one of the
  most important crops grown in North America
• Rusts are caused by a type of basidiomycete that
  needs two different plants to complete its life
  cycle
• Spores produced by rust in barberry plants are
  carried by the wind into wheat fields
• There, the spores germinate and infect wheat
  plants
• The patches of rust produce a second type of
  spore that infects other wheat plants, allowing
  the disease to spread through the field like
  wildfire

96
Plant Diseases 

• Later in the growing season, a new variety of
  spore is produced by the rust
• These tough black spores easily survive through
  the winter
• In spring, they go through a sexual phase and
  produce spores that infect barberry plants
• Once on the barberry leaves, the rust produces
  the spores that infect wheat plants, and the
  cycle continues
• Fortunately, once agricultural scientists
  understood the life cycle of the rust, they were
  able to slow its spread by destroying barberry
  plants

97
Human Diseases 

• Fungal parasites can also infect humans
• One deuteromycete can infect the areas between
  the toes, causing the infection known as
  athlete's foot
• The fungus forms a mycelium directly within the
  outer layers of the skin
• This produces a red, inflamed sore from which the
  spores can easily spread from person to person
• When the same fungus infects other areas, such as
  the skin of the scalp, it produces a red scaling
  sore known as ringworm, which is not a worm at
  all

98
FUNGAL DISEASES
99
Human Diseases 

• The microorganism Candida albicans, a yeast, can
  disrupt the equilibrium within the human body,
  causing fungal disease
• Candida, which grows in moist regions of the
  body, is usually kept in check by competition
  from bacteria that grow in the body and by the
  body's immune system
• This normal balance can be upset by many factors,
  including the use of antibiotics, which kill
  bacteria, or by damage to the immune system
• When this happens, Candida may produce thrush, a
  painful mouth infection
• Yeast infections of the female reproductive tract
  usually are due to overgrowth of Candida

100
FUNGAL DISEASES
101
Other Animal Diseases 

• As problematic as human fungal diseases can be,
  few fungal diseases are as deadly as the
  infection by one fungus from the genus Cordyceps
• This fungus infects grasshoppers in rain forests
  in Costa Rica
• Microscopic spores become lodged in the
  grasshopper, where they germinate and produce
  enzymes that slowly penetrate the insect's tough
  external skeleton
• The spores multiply in the insect's body,
  digesting all its cells and tissues until the
  insect dies
• To complete the process of digestion, hyphae
  develop, cloaking the decaying exoskeleton in a
  web of fungal material
• Reproductive structures, which will produce more
  spores that will spread the infection, then
  emerge from the grasshopper's remains, as shown
  in the photograph

102
Grasshopper Infected by a Fungus 

• This grasshopper is the victim of Cordyceps, a
  fungus
• Once the fungus's tiny spore enters the insect's
  body, it multiplies rapidly and digests body
  tissues
• The structures growing out of the grasshopper's
  body are the fungus's fruiting bodies

103
Grasshopper Infected by a Fungus 
104
Symbiotic Relationships

• Fungi often grow in close association with
  members of other species in symbiotic
  relationships
• Although fungi are parasites in many of these
  relationships, that is not always the case
• Some fungi form symbiotic relationships in which
  both partners benefit
• Two such mutualistic associations, lichens and
  mycorrhizae, are essential to many ecosystems

105
Lichens

• Lichens are not single organisms
• Rather, they are symbiotic associations between a
  fungus and a photosynthetic organism
• The fungi in lichens are usually ascomycetes,
  although a few are basidiomycetes
• The photosynthetic organism is either a green
  alga or a cyanobacterium, or both
• The figure below shows the structure of a lichen

106
Structure of a Lichen  

• Lichens are a mutualistic relationship between a
  fungus and an alga or a cyanobacterium, or both
• The protective upper surface of a lichen is
  composed of fungal hyphae
• Below this is the layer of cyanobacteria or algae
  with loosely woven hyphae
• The third layer consists of loosely packed hyphae
• The bottom layer is a protective surface covered
  by small projections that attach the lichen to a
  rock or tree

107
Structure of a Lichen  
108
Lichens

• Lichens are extremely resistant to drought and
  cold
• Therefore, they can grow in places where few
  other organisms can surviveon dry, bare rock in
  deserts and on the tops of mountains
• Lichens are able to survive in these harsh
  environments because of the relationship between
  the two partner organisms
• The algae or cyanobacteria carry out
  photosynthesis, providing the fungus with a
  source of energy
• The fungus, in turn, provides the algae or
  bacteria with water and minerals that it collects
  and protects the delicate green cells from
  intense sunlight

109
Lichens

• Lichens are often the first organisms to enter
  barren environments, gradually breaking down the
  rocks on which they grow
• In this way, lichens help in the early stages of
  soil formation
• Lichens are also remarkably sensitive to air
  pollution, and they are among the first organisms
  to be affected when air quality deteriorates

110
SYMBIOTIC RELATIONSHIPTOP MYCORRHIZAEBOTTOM
FOLIOSE LICHEN
111
MUTUALISM

• Type of symbiosis in which both organisms benefit

112
MYCORRHIZAE

• Symbiotic association between fungi and plant
  roots
• Occurs in about 80 of plants
• Helps plants absorb water and nutrients, such as
  phosphorus and potassium, by forming extensive
  networks of fungal hyphae in the soil increasing
  the surface area in the soil for absorption
• Digestive action of the fungal enzymes provides
  nutrients that can be readily absorbed by the
  plant
• Fungi absorbs some of the sugars created by the
  plant during photosynthesis

113
Mycorrhizae

• Fungi also form mutualistic relationships with
  plants
• Almost half of the tissues of trees are hidden
  beneath the ground in masses of tangled roots
• These roots are woven into a partnership with an
  even larger web of fungal mycelia
• These associations of plant roots and fungi are
  mycorrhizae (singular mycorrhiza)

114
Mycorrhizae

• Scientists have known about this partnership for
  years, but recent research shows that it is more
  common and more important than was previously
  thought
• Researchers now estimate that 80 percent of all
  plant species form mycorrhizae with fungi

115
Mycorrhizae

• How do plants and fungi benefit from each other?
• The tiny hyphae of the fungi aid plants in
  absorbing water and minerals
• They do this by producing a network that covers
  the roots of the plants and increases the
  effective surface area of the root system
• This allows the roots to absorb more water and
  minerals from the soil
• In addition, the fungi release enzymes that free
  nutrients in the soil
• The plants, in turn, provide the fungi with the
  products of photosynthesis

116
Mycorrhizae

• The presence of mycorrhizae is essential for the
  growth of many plants
• The seeds of some plants, such as orchids, cannot
  germinate in the absence of mycorrhizal fungi
• Many trees are unable to survive without fungal
  symbionts
• Mycorrhizal associations have even been cited as
  an adaptation that was critical in the evolution
  of land plants from more-aquatic ancestors

117
Mycorrhizae

• Mycorrhizal relationships are often very
  specialized
• For example, the Douglas fir forests of the
  Pacific Northwest are dependent on the presence
  of a particular species of white truffle
• In Europe, black truffles are found growing with
  oak and beech trees
• The fly agaric grows mostly with birch and pine
  trees

118
Mycorrhizae

• Why is this networking relationship so important?
• The partnership between plant and fungus does not
  end with a single plant
• The roots of each plant are plugged into
  mycorrhizal networks that connect many plants
• What's more astounding is that these networks
  appear to connect plants of different species

119
Mycorrhizae

• A recent experiment showed that carbon atoms from
  one tree often end up in another nearby tree
• In an experiment using carbon isotopes to track
  the movement of carbon, ecologist Suzanne Simard
  found that mycorrhizal fungi transferred carbon
  from paper birch trees growing in the sun to
  Douglas fir trees growing in the shade
• As a result, the sun-starved fir trees thrived,
  basically by being fed carbon from the birches

120
Mycorrhizae

• Simard's findings suggest that plants are far
  from being isolated individuals, as was
  previously thought
• Instead, plantsand their associated fungimay be
  evolving as part of an ecological partnership