Fungi
31.1 Fungal Lifestyles and Physiology
 Kingdom of Fungi
 Fungi are heterotrophs, like animals, meaning that they cannot
produce their own food.
o Fungi do not directly eat or ingest their food.
o Exoenzymes
 This absorptive mode of nutrition is related to the diverse life
styles exhibited by fungi
o Decomposers (Saprobes)
 Break down and absorb nutrients from non-living
organic material
 This picture shows some black fungus decomposing
the cellulose of the cells of this tree
o Parasites
 Absorb nutrients from the cells of living hosts.
 This picture shows the parasitic fungi Cordyceps, which
infects its host’s mind, and grows out of their bodies.
o Mutualistic Fungi
 Also absorb nutrients from a host organism, but in turn
reciprocate by performing functions beneficial to the
host.
 E.g. aiding a plant in the uptake of minerals from soil
 This picture shows Lacarria Bicolour, which provides
the tree roots it affects with essential nutrients in
return for sugar
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Body Structure
The bodies of fungi typically form a network of tiny filaments
called hyphae
o Hyphae are composed of tubular cell walls surrounding the
plasma membrane and cytoplasm of the cells.
o Unlike the cellulose walls of plants, fungal cell walls contain
chitin.
o This picture shows a fungal hyphus growing out of a rotting
log
Fungal Hyphae form an interwoven mass called a Mycelium.
o The mycelium surrounds and infiltrates the material on
which the fungus feeds.
o The structure of the mycelium maximizes the ratio of
surface area to its volume.
o Fungal mycelia grow rapidly.
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In most fungi, hyphae are divided into cells by cross-walls, or
septa.
o Septa generally have pores large enough to allow ribosomes,
mitochondria, and even nuclei to flow from cell to cell.
Some fungi lack septa, and they are known as Coenocytic fungi.
o They consist of a continuous cytoplasmic mass containing
hundreds or thousands of nuclei.
Some fungi have specialized hyphae that allow them to feed on
living animals.
Other species have specialized hyphae called Haustoria that
enable them to penetrate the tissue of their hosts.
o Mutually beneficial relationships between such fungi and
plant roots are called Mycorrhizae.
 Ectomycorrhizal fungi form sheaths of hyphae over the
surface of a root and also grow into the extracellular
spaces of the root cortex
 Endomycorrhizal fungi extend their hyphae through
the root cell wall and into tubes formed by pushing the
root cell membrane inward. (Invagination)
31.4 Fungal Phylogeny
Chytrids
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Fungi ubiquitous in lakes and soil
Phylum chytridiomycota
Possess Zoospores, which are spores that have flagella.
Some form colonies with hyphae, while others exist as single
spherical cells.
Zygomycetes
 Includes fast-growing molds responsible for produce rotting, as
well as parasites and commensal symbionts of animals.
 During sexual reproduction, zygosporangium are formed.
 Zygosporangium contain many haploid nuclei from each parent
 Inside the zygosporangium, karyogamy and meiosis occur.
 Karyogamy is the fusion of the haploid nuclei to form diploid
nuclei
 The zygosporangium’s hard case eventually germinates into a
sporangium, and produces the fungus’ spores, and releases them
when ready
 Zygosporangia are resistant to freezing and drying, and are
metabolically inactive
Microsporidia
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Unicellular parasites of animals and protists
Often used in control of insect pests
Lack a conventional mitochondria
The lack of mitochondria makes them a mystery to researchers in
terms of taxonomy, being unsure of when and where exactly they
branched from the evolutionary tree
 Instead of mitochondria, they very tiny organelles which were
derived from mitochondria
 Some researches actually believe that they should be classified as
zygomycetes
 Infect the vacuoles of an animal cell to obtain nutrients and to
reproduce
Glomeromycetes
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Formerly thought to be zygomycetes
Only 160 species in this phylum
Form a unique arbuscular mycorrhizae
Their hyphae push into plant root cells and branch out within
Form symbiotic relationships with many plants
That picture shows the species called Dead Man’s fingers
Ascomycetes
 Most defining feature is the production of a saclike asci, in which
spores are formed
 Commonly called sac fungi
 Bear their sexual stages in fruiting bodies, called ascocarps.
 They vary in size and complexity, from yeasts to elaborate cup
fungi
 Many ascomycetes live in symbiotic relationships with algae or
cyanobacteria, known as lichens
 Reproduce asexually by producing enormous numbers of asexual
spores called conidia
 Unlike other fungi, the asexual spores of ascomycetes are formed
externally at the tips of specialized hyphae called conidiophores
from which they are dispersed by the wind
 If the conidia land near the mycelia of a mating type, it will fuse to
it, and enter sexual reproduction
 The asci formed in the place where the two meet acts as a safe
production centre for the ascospores, which have DNA from both
parent fungi
 The ascospores are discharged in a similar fashion to the conidia
Basidiomycetes
 Name is derived from the basidium – a cell which undergoes a
transient diploid stage during the fungal life cycle, which
basidiomycetes possess
 Known for their distinct “club-like” shape
 Important decomposers of wood and other plant material
 Reproduce sexually by producing elaborate fruiting bodies called
basidiocarps, in which sexual reproduction begins
 Each basidiocarp has many basidia within it, which look like gills.
Inside each of these, the spores are produced, which can number
up to one billion when released.
 Asexual reproduction is less common in basidiomycetes than in
ascomycetes
31.5 Fungal Impact on Humans and Ecosystems
Decomposers
 Fungi are well-adapted to consume and break down many organic
materials
 For any carbon-containing substrate, there are atleast some fungi
that can consume it, including jet fuel and paint
 Necessary for returning nutrients to the soil that have been
previously absorbed by other living organisms
Symbionts
 Some fungi form symbiotic relationships with animals
o I.e. Ants bringing leaves to fungi, which decompose them
into an edible form.
Lichens
 Lichens are a symbiotic association of millions of photosynthetic
microorganisms held in a mass of fungal hyphae.
 Look like a carpet found growing on rock
 The photosynthetic partners are typically unicellular or
filamentous green algae, or cyanobacteria.
 The fungal component is most often an ascomycete
 The algae provide carbon compounds and organic nitrogen, while
the fungi provide a suitable environment for growth, and assist
the algae in the uptake of minerals through the secretion of acids.
 The fungal components of many lichens reproduce sexually by
forming asocarps or basidiocarps.
 Asexual reproduction occurs commonly through fragmentation, or
by formation of soredia, which are small clusters of hyphae with
embedded algae.
Pathogens
 About 30% of fungi live their lives as parasites.
 Fungi such as Ophiostoma Ulmi, can have severe effects on plants
or animals.
 Between 10 and 50% of the worlds fruit harvest is lost each year
to fungal attack
 Some fungi that attack food crops are toxic to humans.
 Animals are much less susceptible to parasitic fungi than plants. A
fungal infection in an animal is called mycosis
 Skin mycoses include ringworm, which may appear as red circular
areas on the skin, and is caused by ascomycetes.
 Systemic mycoses spread throughout the body, and generally
cause serious illnesses. These are usually caused by the inhalation
of spores.
Practical Uses of Fungi
 Certain cheeses, such as Roquefort and blue cheese, gain their
distinctive flavours from the fungi used to ripen them
 Humans use yeast to produce alcoholic beverages, and to make
bread rise.
 A compound extracted from ergots is used to reduce high blood
pressure, and to stop maternal bleeding after childbirth.
 Penicillin, the first antibiotic ever discovered, was made by the
ascomycete mold Penecilium.
32: An Introduction to Animal Diversity
32.1 Structure and Development of Animals
Nutritional Mode
 Animals are heterotrophs, meaning that they cannot grow their
own food, and must eat other living or non-living organisms for
nutrition.
o Most animals use enzymes to digest their food only after
they have ingested it.
Cell Structure and Specialization
 Animals are multicellular eukaryotic organisms.
 Animal cells lack the structural support of cell walls.
o They are instead held together by structural proteins.
 The most abundant of these is collagen.
 In addition to collagen, animals have three distinct types of
intercellular junctions.
o Tight Junctions, Desmosomes, and Gap junctions.
o Each consist of different structural proteins
 Animal cells have two types of specialized cells that are not seen
in any other multicellular organisms.
o Muscle Cells and Nerve Cells.
 These cells are responsible for movement and impulse
conduction respectively.
Reproduction and Development
 Most animals reproduce sexually, with life cycles dominated by
the diploid stage
 A small, flagellated sperm from the male fertilizes the large, nonmotile egg from the female, forming the zygote.
 The zygote then undergoes cleavage, which is a succession of
mitotic cell divisions without cell growth between cycles.
o Cleavage leads to the formation of a multicellular stage
called a blastula
 Following the blastula stage, the process of gastrulation takes
place.
o During gastrulation, layers of embryonic tissues, which will
develop into adult body parts, are produced.
o The stage that results from gastrulation is called a gastrula.
 The life cycle of many animals include at least one larval stage
o A larva is a sexually immature form of an animal that is
morphologically distinct from the adult.
o Animal larvae eventually undergo metamorphosis, which
transforms them into a mature adult.
 Despite the diversity of morphology exhibited by adult animals,
the underlying genetic network that controls animal development
has been relatively conserved.
o All eukaryotes have genes that regulate the expression of
other genes, known as Hox Genes.
 Hox genes play an important role in the development
of animal embryos, and the expression of hundreds of
other genes.
 Since they can control cell division and differentiation,
Hox Genes can produce different morphological
features of animals
32.2 The History of The Animal Kingdom
 Some studies say that animal diversification occurred between 1.5
and 1.2 billion years ago
 Studies on the common ancestor of living animals suggest that it
lived between 1.2 billion to 800 million years ago, and may have
resembled modern choanoflagellates.
Neoproterozoic Era (1 Billion – 542 Million Years Ago)
 The first generally accepted fossils of animal are 575 million years
old
o These are known as the Ediacaran Fauna
 Neoproterozoic rocks have also yielded microscopic signs of early
animals
Paleozoic Era (542-251 Million Years Ago)
 Animal diversification greatly accelerated during this time period,
known as the Cambrian Explosion
 Some studies suggest that this “explosion” was caused by a
predator-prey relationship being developed that caused diversity
through natural selection
 Vertebrates (Early fish) were dominating the marine food chain
during the early Paleozoic era
 By 460 million years ago, Arthropods began adapting to terrestrial
life
 Vertebrates made the transition to land about 360 million years
ago and diversified into numerous terrestrial lineages
Mesozoic Era (251-65.5 Million Years Ago)
 Period began with the Permian-Triassic mass extinction, in which
96% of marine species, and 70% of terrestrial vertebrates were
wiped out.
 There was very little in terms of morphological diversification
during this time period
 Animals that had evolved during the Paleozoic era began to
spread into new ecological niches
o The first coral reefs were forming in the oceans
o Some reptiles were returning to the water
o Large dinosaurs emerged
o The first mammals, tiny nocturnal insect-eaters appeared as
well
Cenozoic Era (65.5 Million Years Ago – Present)
 Began with the cretaceous-tertiary mass extinction
 End of the dinosaurs
 Insects and plants underwent a dramatic diversification during
this period
 This era began with the mass extinctions of both terrestrial and
marine animals.
 Mammals began to expand and explore different ecological
niches, thriving through the mass extinction
32.3 Animal “Body Plans”
 A group of animal species that share the same level of
organizational complexity is known as a Grade
o The set of morphological and developmental traits that
define a grade are generally integrated into a function
referred to as a body plan.
Symmetry
 Some animals exhibit radial symmetry, i.e. jellyfish and sea
anemones
 Others may exhibit bilateral symmetry
o Bilateral animals have a dorsal side and a ventral side, as
well as a left and right, an anterior, and a posterior side.
o I.e. Lobsters
o Many animals that display bilateral symmetry have sensory
equipment concentrated at the anterior end, i.e. a brain.
Tissues
 True tissues are collections of specialized cells isolated from other
tissues by membranous layers.
 In all animals except for sponges, when the embryo undergoes
gastrulation it becomes layered in tissues.
 These concentric layers that form are called germ layers
o The outer covering of an animal is created by the Ectoderm
germ layer
o Endoderm is the innermost germ layer, which lines the
developing digestive tract and related organs
 Animals that have only endoderm and ectoderm are known as
Diploblastic.
 Most other animals have a third layer called the mesoderm,
which lies between the other two.
o These animals are said to be triploblastic
o In triploblasts, the mesoderm forms the muscles and most
other organs.
Body Cavities
 Some triploblastic animals possess a body cavity, which is a fluidfilled space separating the digestive tract from the outer body
wall
o This body cavity is also known as a coelom
o A “true” coelom forms from tissue derived from the
mesoderm
o Animals that possess a true coelom are known as
coelomates
 Some triploblastic animals have a body cavity formed from the
blastocoel
o This cavity is called a pseudocoleom, and the animals are
pseudocoelomates
 Some triploblastic animals lack a coelom altogether, and are
known as acoelomates
 A body cavity cushions the suspended organs to prevent injuries
 In soft-bodied coleomates, the coelom contains noncompressible
fluid, which acts as a skeleton
Protosome and Deuterostome Development
 Many animals can be categorized as having one of two
developmental modes. They are protostome development, and
deuterostome development
 These modes are often distinguished by three features
Cleavage
 Many animals with protostomal development show a pattern of
spiral cleavage.
o Planes of cell division are diagonal to the vertical axis of the
embryo
o Determinate Cleavage is shown in these animals, which
casts the developmental fate of embryonic cells at a very
early stage.
 Deuterosomal development is predominantly characterized by
radial cleavage.
o The cleavage planes are either parallel or perpendicular to
the vertical axis of the egg.
o Indeterminate Cleavage, exhibited by these animals, allow
cells to retain the capacity to develop into a complete
embryo, instead of determining the final product early on
Coelom Formation
 In protostomal animals, the coelomic cavity is formed by solid
masses of mesoderm splitting as the archenteron forms. This is
known as schizocoelous development.
 In deuterostomal animals, the mesoderm buds from the wall of
the archenteron, and the cavity formed becomes the coelom. This
is known as enterocoelous development.
Fate of the Blastospore
 The blastospore is the indentation that, during gastrulation,
leads to the formation of the archenteron.
 The difference in the fate of the blastospore is determined by
which end of the digestive tract is formed at the blastospore
 In protostomes, the mouth is developed from the blastospore
 In deuterostomes, the anus is formed from the blastospore