Fungi
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Interesting facts about fungi
There are more than 60 species of fungi that
exhibit the phenomenon of emitting light from
their bodies known as bioluminescence.
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People eat mushrooms of all shapes, sizes and
colors. Yeasts are used in making bread, wine, beer
and solvents.
Drugs made from fungi cure diseases and stop the
rejection of transplanted hearts and other organs.
Fungi are also grown in large vats to produce
flavourings for cooking, vitamins and enzymes for
removing stains.
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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.
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Features of Fungi
• Heterotrophic (Do not make their
own food)
• No chlorophyll
• Mostly multi-cellular
• Made up of threads called
hyphae
• Hyphae combine in masses to
form a mycelium
• Their walls are made of a
carbohydrate called chitin
(found in insect bodies)
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Features
• They reproduce by means of spores.
• They do not ingest food but instead they
secrete enzymes onto their food and then
absorb the nutrients through their rhizoids.
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Nutrition
All fungi are heterotrophs i.e. they take in food made
by other organisms.
Edible fungi e.g. field mushrooms, truffles
Poisonous fungi e.g. death cap
Fungi are either:
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Parasitic
•
Saprophytic
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Nutrition
1. Parasites
Live off a live host and cause harm.
e.g. athletes foot or ringworm.
Obligate parasites can
only live off a host and not on
their own. e.g. smuts and rusts.
2. Saphrophytes
Most fungi are saphrophytes and these live off dead
material. e.g. ear fungus on dead wood. They are essential
for recycling nutrients.
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Parasitic Fungi
• Obligate parasites
– live on live hosts but
do not normally kill
them
• Facultative parasites
– kill the host and feed
on the remains
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• 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
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Rhizopus
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Bread Mould (Rhizopus)
This fungus grows on the starch in bread,
vegetable peelings and stored fruits.
Digestion takes place outside of the fungus
and the nutrients are absorbed.
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Rhizopus
Structure
• The mould is often called pin mould as it's
reproductive
• structures look like pins.
• Tubes called hyphae form a big mass called a
mycelium.
• The hyphae digest and absorb the starch in the
bread.
• A stolon is an aerial hyphae (stands up) which
allows the mould to spread more quickly.
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Rhizopus growing on agar
Structure of Rhizopus
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Rhizopus to Label
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Functions of parts of Rhizopus
Part
Function
Hyphae
Mycelium
Spread the fungus &
absorb nutrients
Spread the fungus
Sporangium
Produces the spores
Sporangiophore
Holds up the sporangium
Stolon
Allows fungi to spread
Columella
Spore release
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Structure of Rhizopus
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Facts about bread mould:
1. Bread mould consists of threadlike structures
called Hyphae
2. Hyphae are tubular with no cross walls and are
multinucleate. Each nucleus is haploid.
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3. Large numbers of hyphae are called a mycelium
4. The hyphae digest the substrate on which they
grows
5. Rhizoids provide extra surface area for absorption
of the digested material
6. Stolons are arial hyphae which allow Rhizopus to
spread sideways
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Sporangium
Spores
Columella
Apophysis
Sporangiophore
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Rhizopus: Sporangia
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Life cycle of Rhizopus
Two types of reproduction:
1. Asexual Reproduction
2. Sexual Reproduction
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Asexual reproduction in Rhizopus
• Only involves one parent.
• Does not involve fertilisation
• Offspring are identical to parent
1. Hyphae called sporangiospores grow
up into the air. Their tips swell to form
sporangium.
2. Cells inside the sporangium produce
haploid spores by mitosis.
(Sporulation is the process of
making spores).
3. In dry conditions the sporangium
opens and spores are released.
4. Spores are carried by the wind and if
they land on a suitable substrate
they
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germinate.
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Spores being released from
Sporangium
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Sexual Reproduction
• Involves two parents
• Involves fertilisations and offspring are not
identical to parents.
Rhizopus doesn't have a male or female but
we call them + or - .
Both look identical but sexual reproduction
needs a plus and a minus strain to
happen.
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Steps in Sexual Reproduction
1.Hyphae from opposite strains grow close together.
2. Swellings form opposite each other.
3. The swellings touch.
4. Nuclei (gametes) move into each swelling.
5. Cross walls form and form gametangia.
6. The walls dissolve.
7. Many fertilisations happen to make diploid
zygote nuclei.
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Sexual Reproduction
8. A tough walled black zygospore forms
around the nuclei.
9. Zygospore germinates by meiosis when
conditions are right.
10. A haploid hyphae grows out and makes
a sporangiophore with a sporangium This
produce new haploid spores which can
grow.
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Sexual reproduction
• Sexual reproduction
in Rhizopus can only
occur between a plus
and a minus strain.
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+ Strain
- Strain
Sexual reproduction
• When hyphae from
opposite strains grow
close together
swellings grow on
both strains and touch
each other.
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+ Strain
- Strain
Sexual reproduction
• Nuclei from both
hyphae move into
these swellings which
are now called
progametangia.
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+ Strain
- Strain
Sexual reproduction
• Cross-walls form to
produce gametangia.
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+ Strain
- Strain
Sexual reproduction
• The walls of the
gametangia dissolve
and a number of
fertilisations take
place producing
diploid zygote nuclei.
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+ Strain
- Strain
Sexual reproduction
+ Strain
• A zygospore forms
around these nuclei.
• When conditions are
suitable the
zygospore germinates
by meiosis.
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- Strain
Sexual reproduction
+ Strain
• A zygospore forms
around these nuclei.
• When conditions are
suitable the
zygospore germinates
by meiosis.
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- 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.
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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
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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
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Yeast
The yeast fungus consists of single
cells rather than hyphae
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Structure of yeast
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Yeast
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Another name for yeast is Saccharomyces.
They can be round or oval in shape.
They can usually only be seen with an
electron microscope.
Yeast have thin walls made of chitin.
They have a thick cytoplasm with many food
storage vacuoles.
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Respiration in Yeast
Respiration
• Yeasts respire anaerobically (without
Oxygen) and break down glucose to
produce ethanol (alcohol) and Carbon
Dioxide.
• Glucose 2 Ethanol + 2 Carbon dioxide.
• This process is called fermentation.
• Fermentation is a type of anaerobic
respiration
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Reproduction in Yeast
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Reproduction in Yeast
Asexual Reproduction
This is done by budding.
The parent cell divides by Mitosis and the
new nucleus and cytoplasm enter the new
cell.
If the buds don't separate they form a colony
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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.
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Asexual reproduction in yeast
• This bud can
separate from the
parent to become a
new individual
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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
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Budding
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Budding
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Economic importance of fungi
Beneficial fungi
• Making bread and
alcohol e.g. wine and
beer.
• Fungi can be used as
a source of food e.g.
mushroom
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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
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Decomposition
Certain species of fungi and bacteria are decomposers.
Over time, without decomposition, so much nitrogen
would be locked up in leaves and other tissues that there
would not be enough nitrogen available for the plant to
make new leaves, stems and wood.
The surface of the ground would also be buried by dead
leaves and wood lying forever where they fell.
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Experiment to grow leaf yeast
Sterile means that all microorganisms
are destroyed. i.e. there is nothing living.
For this experiment we Ash or Ivy leaves. We cut them into
circles and stick them face up to the inside of the dish lid.
The yeast spores drop off the leaves onto the agar. They
start to grow and form pink colonies.
Important to keep the bench sterile we wash our
hands, the desk and all equipment with disinfectant.
We also put the tweezers etc. through a bunsen flame.
This is Saccharomyces roseus.
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What have you learned?
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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
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