Bio 20: Diversity of Life
Fungi - Teacher Notes
Kingdom Fungi
Fungi belong to the
Domain Eukarya and
Kingdom Fungi.
Characteristics
 Unicellular or
multicellular
 Eukaryotic
 Heterotrophic
 Decomposers
Major Features
Cell Walls
Unlike plant cells which have cell walls composed of cellulose, fungal cells have
cell walls composed of chitin (pronounced KI tun). Chitin is a strong flexible
carbohydrate.
Hyphae (pronounced HI fee)
The body of a multicellular fungus is composed of thread-like filaments called
hyphae. Hyphae grow at their tips and branch to form a netlike mass called
mycelium.
The large surface area of hyphae helps the fungus to obtain nutrients.
In mushrooms, it is difficult to see individual hyphae yet they compose the above
ground reproductive structure (called the fruiting body) and the underground
mycelium.
Bio 20: Diversity of Life
Fungi - Teacher Notes
Cross-walls
In many fungi, hyphae are divided into cells by cross-walls called septa. The septa
have large pores that allow nutrients, cytoplasm, organelles, and even nuclei to
flow between cells.
Some fungi are aseptate, meaning they have no septa. In this case, the
cytoplasm, nuclei, nutrients and other materials flow freely and very quickly.
Bio 20: Diversity of Life
Fungi - Teacher Notes
Nutrition in Fungi
All fungi are heterotrophs, but unlike humans who ingest their food and then
digest it, fungi digest their food before they ingest it.
Many fungi produce enzymes that break down organic material, allowing the
nutrients to be absorbed through their cell walls.
Fungi can get nutrients by being:
1. Saprophytic – A saprobe is an organism that feeds on dead organisms. These
fungi are important decomposers and recycler of nutrients in food webs. (e.g.
Bracket fungus live on decaying trees.)
2. Parasitic – These fungi absorb nutrients from the living cells of a host organism
and cause harm to the host. (e.g. Athlete’s foot is caused by a group of parasitic
fungi called dermatophytes.)
3. Mutualistic – Some fungi live in beneficial relationships with other organisms,
such as plants or algae. (e.g. The mycelia of a particular fungus cover the root of a
soybean plant. The fungus receives sugar from the host while the mycelia
increase water and nutrient uptake for the host plant.)
Reproduction in Fungi
Many fungi can reproduce both asexually and sexually although asexual methods
are more common.
Asexual reproduction can occur through mitosis, budding, fragmentation, and
spores. Asexual methods result in the production of genetically identical offspring.
Sexual reproduction in fungi occurs when nutrients or water are scarce. It
produces genetically different organisms. Sexual reproduction occurs via the
production of spores by meiosis.
Bio 20: Diversity of Life
Fungi - Teacher Notes
Asexual Reproduction
1. Budding – Unicellular yeast cells reproduce asexually by budding. The daughter
cell develops while still attached to the parent cell. The cell membrane pinches
off to partially separate the daughter cell from the parent cell.
2. Fragmentation – When the mycelium is physically broken apart (say from an
animal digging in the soil), the fragmented hyphae will grow into new mycelia.
E.g. dermatophytes that can cause athlete’s foot
3. Spore production
A spore is a reproductive haploid cell with
a hard outer coat that develops into a
new organism. It does not require the
fusion of gametes (sex cells) to produce
new individuals.
Hyphae produce sporangia (plural –
sporangium, single) (specialized
reproductive structures), which in turn
produce haploid spores.
These spores are released and carried by
air, animals, water, and insects.
When spores land on moist nutrient-rich
surfaces, new hyphae form.
Bio 20: Diversity of Life
Fungi - Teacher Notes
Sexual Reproduction
Haploid hyphae from two different fungi act as gametes.
There are no male and female fungi, just plus (+) and minus (-) strains.
When the plus and minus hyphae fuse, a zygote is formed (now diploid).
The zygote matures and undergoes meiosis to produce new haploid hyphae,
which can then germinate to produce new fungus.
Bio 20: Diversity of Life
Fungi - Teacher Notes
Adaptations for Survival
Most fungi produce trillions of spores. This ensures
that at least a few spores will land in suitable locations
and begin to grow.
Spores are lightweight and small so that wind and even
the tiniest organisms can transport them.
Spores have a have a strong, waterproof outer wall
which allows them to survive in extreme temperature
and moisture conditions.
Vocabulary
Diploid – cell with a full number of chromosomes (2n)
Haploid – cell with half the number (n) of chromosomes as a diploid (2n) cell
Gamete – a haploid sex cell that can combine with another haploid sex cell and produce a
diploid cell
Meiosis – process in which one diploid (2n) cell produces four haploid (n) cells that are not
genetically identical
Mitosis – process in which a cell’s replicated DNA divides and two genetically identical diploid
(2n) daughter cells are produced
Zygote – fertilized egg
Read in the text pages 438-440.
Bio 20: Diversity of Life
Fungi - Teacher Notes
Classification of Fungi
The fruiting body of a spore-forming fungus is called a sporophore. Fungi are
classified based on the type of sporophore they exhibit.
The four major phyla within Kingdom Fungi are Chytridiomycota, Zygomycota,
Ascomycota, and Basiodiomycota.
1. Phylum Chytridiomycota (Chytrids)
Chytrids are unique among fungi because they are aquatic and produce
flagellated spores. As such, they used to be classified with protists. However, the
presence of chitin in cell walls and recent biochemical evidence have shown that
chytrids are more closely related to fungi.
It is likely they are the evolutionary link between fungus-like protists and fungi.
Bio 20: Diversity of Life
Fungi - Teacher Notes
2. Phylum Zygomycota (Common Moulds)
Zygomycetes are multicellular and terrestrial. For example - Rhizopus stolonifer,
black bread mould that grows on bread and other foods.
Moulds form a type of hyphae called stolons that spread horizontally across the
surface of food. Rhizoids, another type of hyphae, penetrate the food and absorb
nutrients. Sporangiophores, yet another type of hyphae, push up into the air and
form sporangia at their tips.
Zygomycetes reproduce asexually via the release of thousands of haploid spores
from sporangia.
In poor environmental conditions
zygomycetes can reproduce sexually.
A plus (+) hyphae and (-) hyphae
come together, forming a
gametangium. The haploid gametes
from the mating types then fuse
together to form a diploid zygote.
The zygote develops a thick wall and
becomes a dormant zygospore.
When conditions improve the
zygospore will germinate and
sporangiophores and sporangia will
develop.
Bio 20: Diversity of Life
Fungi - Teacher Notes
3. Phylum Ascomycota (Sac Fungi)
There are more than 60,000 species of fungi found in this phylum! Although the
most well known ascomycete – yeast – is unicellular, most members of this
phylum are multicellular. For example – edible morels and truffles.
During asexual reproduction, spores are formed at the tips of hyphae called
conidiophores. The spores they generate are called conidia.
During sexual reproduction, the fusion of two mating types occurs within a
specialized reproductive structure called an ascocarp. Once the haploid gametes
form a diploid zygote, cell division occurs and the new cells develop into spores in
the ascus, a saclike structure which gives the phylum its name. Spores produced
by an ascus are called ascospores.
Bio 20: Diversity of Life
Fungi - Teacher Notes
4. Phylum Basidiomycota (Club Fungi)
Basidiomycetes are multicellular and terrestrial. For example -mushrooms,
bracket fungi and puffballs.
Basidiomycetes reproduce sexually by forming a basidiocarp, made up of a stalk
and flattened cap. Gills are found on the underside of the cap and are lined with
basidia, club shaped hyphae that produce spores. Spores produced by a basidium
are called basidiospores.
Deuteromycota (Imperfect Fungi)
This is a diverse group that share only one trait – no sexual reproduction has ever
been observed. Because of this, these fungi are referred to as imperfect. Further
classification of these species is pending.
Interestingly, the antibiotic Penicillin is produced by a deuteromycote.
Bio 20: Diversity of Life
Fungi - Teacher Notes
Ecology of Fungi
Symbiosis is a relationship where 2 different organisms live in close association.
This includes commensalism, mutualism, and parasitism.
Mutualism is where both organisms benefit from the association.
 E.g. lichens and mycorrihizae
Lichens
 Symbiotic relationship between a fungus
and a photosynthetic green algae
 Both organisms benefit
o algae makes food through
photosynthesis
o fungus supplies moisture, shelter,
and anchorage
 Grow on rocks, trees, and buildings.
 Considered to be pioneer species
because the fungus component breaks
down rock into soil over a long period of
time.
Mycorrhizae
 Symbiotic relationship between a fungus and plant roots
 Plants with mycorrhiza are healthier than plants without them.
 Both organisms benefit
o Fungus absorbs sugars made by plant
o Plants absorb more water and minerals with aid of the fungus
 Most plants have mycorrhizae on their roots
Bio 20: Diversity of Life
Fungi - Teacher Notes
Importance of Fungi
Like bacteria, fungi can be both help helpful and harmful.
Helpful
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Yeasts are used to make beer & bread
Antibiotic penicillin
Decomposers & recyclers of nutrients
Mushrooms eaten as food
Help form many soft cheeses
Aspergillus is used to make soy sauce
Harmful
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Fungal spores cause allergies
Molds, mildew, rusts, & smuts damage
crops
Cause diseases (athlete’s foot, ringworm)
Poisonous mushrooms
Can cause yeast infections
Read in the text pages 440-443.