Fungi
Learning Objectives
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Define the terms: saprophytic & parasitic
State the structure & life cycle of Rhizopus
Explain nutrition in fungi.
Outline the structure & reproduction of Yeast
Name 2 Beneficial & 2 Harmful fungi
Mention that there are Edible and Poisonous
fungi
Identify and state functions for the following
structures: rhizoid, sporangium, gametangium,
zygospore.
Features of Fungi
• They do not make their
own food
• They are mostly multicellular
• They are made up of
threads called hyphae
• Hyphae combine in
masses to form a
mycelium
• Their walls are made of a
carbohydrate called
chitin
Nutrition
• All fungi are heterotrophs i.e. they take in food
made by other organisms
Fungi are either:
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Parasitic
•
Saprophytic
Saprophytic fungi
• Most fungi are
saprophytic
• obtain nutrients from
dead material
• As they digest it
minerals are released
and recycled
• Play a vital role in the
environment as they
are responsible for
decay
• E.g. mushrooms and
moulds
Parasitic Fungi
• Absorb their food
from live hosts
• They get their food
mostly from plants
although some fungal
parasites live on
animals e.g. athlete’s
foot
http://upload.wikimedia.org/wikipedia/com
mons/thumb/4/4a/Athletes.jpg/220pxAthletes.jpg
Parasitic Fungi
• Obligate parasites
– live on live hosts
but do not
normally kill them
• Facultative
parasites
– kill the host and
feed on the
remains
http://upload.wikimedia.org/wikipedia/com
mons/thumb/4/4a/Athletes.jpg/220pxAthletes.jpg
Symbiosis
• Some fungi e.g. form
symbiotic
relationships with
other organisms
• A lichen is an
organism which is a
combination of a
fungus and an alga
Edible and poisonous fungi
• Some fungi are
edible, but many are
poisonous if eaten
• It is often difficult to
distinguish between
the edible and
poisonous varieties
growing in the wild
Learning Check
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What is a saprophytic fungi?
Give an example of a saprophytic fungi
What is a parasitic fungi?
What is an obligate parasite?
What is facultative parasite?
Give an example of a parasitic fungi
Rhizopus
Rhizopus growing on agar
Structure of Rhizopus
Consists of threadlike structures called Hyphae
Hypha
They are tubular with no cross walls and are
multinucleate. Each nucleus is haploid.
Nucleus
Large numbers of hyphae are called a mycelium
•The hyphae digest the substrate on which they grows
•Rhizoids provide extra surface area for absorption of
the digested material
•Stolons are arial hyphae which allow Rhizopus to
spread sideways
Structure of Rhizopus
Sporangium
Spores
Columella
Apophysis
Sporangiophore
Learning Check
• Can you draw and label the structure of
Rhizopus?
• What is a hypha?
• What is a mycelium?
• What is the function of a rhizoid?
• What is a stolon?
Life cycle of Rhizopus
Asexual reproduction
• Sporangiophores
grow up from the
substrate after a
number of days
• Cells within the
sporangium divide
by mitosis to
produce spores
(haploid)
Asexual reproduction
• Cells within the
sporangium divide
by mitosis to
produce spores
(haploid)
Asexual reproduction
• The sporangium dries
out in the right
conditions and opens
releasing many
spores.
• Each spore will grow
into a new hypha and
mycelium if it lands on
a suitable substrate
Sexual reproduction
• Sexual reproduction
in Rhizopus can only
occur between a plus
and a minus strain.
+ Strain
- Strain
Sexual reproduction
• When hyphae from
opposite strains grow
close together
swellings grow on
both strains and touch
each other.
+ Strain
- Strain
Sexual reproduction
• Nuclei from both
hyphae move into
these swellings which
are now called
progametangia.
+ Strain
- Strain
Sexual reproduction
• Cross-walls form to
produce gametangia.
+ Strain
- Strain
Sexual reproduction
• The walls of the
gametangia dissolve
and a number of
fertilisations take
place producing
diploid zygote nuclei.
+ Strain
- Strain
Sexual reproduction
• A zygospore forms
around these nuclei.
• When conditions are
suitable the
zygospore germinates
by meiosis.
+ Strain
- Strain
Sexual reproduction
• A zygospore forms
around these nuclei.
• When conditions are
suitable the
zygospore germinates
by meiosis.
+ Strain
- Strain
Sexual reproduction
• A hypha grows out of
the zygospore and
produces a
sporangium at the tip.
• The sporangium
opens releasing many
haploid spores which
grow into new
individuals.
Review of sexual reproduction
• Sexual reproduction in Rhizopus can only
occur between a plus and a minus strain
• When hyphae from opposite strains grow
close together swellings grow on both
strains and touch each other
• Nuclei from both hyphae move into these
swellings which are now called
progametangia
• Cross-walls form to produce gametangia
Review of sexual reproduction
• The walls of the gametangia dissolve and a
number of fertilisations take place producing
diploid zygote nuclei
• A zygospore forms around these nuclei
• When conditions are suitable the zygospore
germinates by meiosis
• A hypha grows out of the zygospore and
produces a sporangium at the tip
• The sporangium opens releasing many haploid
spores which grow into new individuals
Learning Check
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How does Rhizopus reproduce?
What is a prometangia?
How is a gametangia formed?
How is a zygospore formed?
What is produced at the tip of a hypha?
Yeast
Structure of yeast
Reproduction in Yeast
Asexual reproduction in yeast
• Asexual reproduction
in yeast occurs by
budding.
• The nucleus of the
parent cell divides by
mitosis. One of the
daughter nuclei
enters a small
developing bud on the
outside of the yeast
cell.
Asexual reproduction in yeast
• This bud can
separate from the
parent to become a
new individual
Asexual reproduction in yeast
• This bud can
separate from the
parent to become a
new individual
• In some cases the
bud does not
separate, but can
itself bud. In this way
long colonies of yeast
cells can develop
Budding
Budding
Economic importance of fungi
Beneficial fungi
• Yeasts can be used
to make bread and
alcohols such as wine
and beer
• Fungi can be used as
a source of food e.g.
mushroom
Economic importance of fungi
Harmful fungi
• Fungi can attack crops
e.g. corn and wheat
and cause major
financial losses as a
result
• Fungi such as athletes
foot and ringworm can
infect animals
• Fungi can spoil food
e.g. rhizopus grows on
bread
Learning Check
• Can you draw the structure of yeast?
• Describe how yeast reproduces
• Give an example of how yeast is important
economically
Syllabus: Depth of treatment
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Saprophytic and parasitic forms
Rhizopus (Structure and life cycle)
Nutrition
Yeast: structure and reproduction
(budding).
Contemporary issues and
Technology
• Mention of edible and poisonous fungi.
• Economic importance of fungi: examples of
any two beneficial and any two harmful
fungi.
Practical Activities
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Investigate the growth of leaf yeasts using
agar plates and controls