Kingdoms
Protista & Fungi
Ch. 17
The Origin of Eukaryotic Cells
• Eukaryotic cells appeared first around 1.7 billion
years ago
– eukaryotic cells possess an internal structure called a
nucleus
The Origin of Eukaryotic Cells
• The endosymbiotic theory is a widely
accepted explanation for the origin of
mitochondria and chloroplasts in
eukaryotes from bacteria
– present-day mitochondria and chloroplasts
still contain their own DNA
• this DNA is remarkably similar in size and
character to the DNA of bacteria
The theory of Endosymbiosis
The Evolution of Sex
•
A profound difference between prokaryotes and eukaryotes is that eukaryotes have the
capacity for sexual reproduction
– sexual reproduction involves two parents contributing gametes to form the offspring
– gametes are usually formed by meiosis and are haploid
– the resulting offspring are diploid
•
But sexual reproduction is not the only way that eukaryotes can reproduce
– many eukaryotes reproduce by asexual reproduction, which is reproduction without
forming gametes
– the offspring of asexual reproduction are genetically identical to the parents
– many eukaryotes reproduce mainly by asexual reproduction, switching to sexual
reproduction only during environmental stress
The Evolution of Sex
• A different asexual strategy in eukaryotes is
parthenogenesis, the development of an adult
from an unfertilized egg
• Many plants and marine fishes undergo a form
of sexual reproduction that does not involve
partners
– this is called self-fertilization and involves one
individual providing both male and female gametes
The Evolution of Sex
• Sexual reproduction is one of the most
important evolutionary innovations of
eukaryotes
– it provides a means of shuffling genes,
creating genetic diversity
• genetic diversity is the raw material of evolution
• the greater the genetic diversity, the more rapid the
evolutionary pace
General Biology of Protists, the Most
Ancient Eukaryotes
• Protists are eukaryotes united on the
basis of a single negative characteristic
– they are not fungi, plants, or animals
– in all other respects, they are highly variable
with no uniting features
Figure 20.5
A unicellular
protist
Figure 20.8 The major protist clades
A Diverse Kingdom
• Euglenozoa: Euglenoids
• Euglena is a representative euglenoid
– two flagella
– contractile vacuole to help
regulate the osmotic
pressure within the organism
– a light-sensitive stigma
which helps this
photosynthetic form find light
– asexual reproduction
Figure 20.9 Euglena
A Diverse Kingdom
• Stramenopila:
Brown algae (phylum Phaeophyta)
– are the longest, fastest-growing, and most
photosynthetically productive living things
– all are multicellular and most are marine
– their life cycle has alternating generations
Figure 20.11(a)
Brown algae
A Diverse Kingdom
• Stramenopila:
Diatoms
(phylum Chrysophyta)
Figure 20.11b Diatoms
– photosynthetic
– encased by unique double
wall of silica
– abundant in both oceans
and freshwater habitats
Fossilized deposits of diatom shells
are mined as “diatomaceous earth.”
A Diverse Kingdom
• Alveolata: Ciliates (phylum Ciliophora)
•
Complex and unicellular
•
possess large numbers of cilia
•
have a defined cell shape and two
nuclei per cell
•
the pellicle is a proteinaceous
scaffold, found inside the plasma
membrane, that confers flexible
support
•
asexual reproduction is by fission
while sexual reproduction is by
conjugation
Figure 20.12 A ciliate
A Diverse Kingdom
• Alveolata: Dinoflagellates (phylum Pyrrhophyta)
– photosynthetic unicellular protists
– usually bear two flagella of unequal length
– a stiff outer coating of cellulose and silica, giving them
unique shapes
Dinoflagellates
A Diverse Kingdom
• Alveolata: Dinoflagellates (continued…)
• some dinoflagellates
produce bioluminescence
or powerful toxins that
cause “red tides”
– “red tides” are population
explosions of these kinds
of dinoflagellates
Figure 20.14 Red tide
A Sporozoan Life cycle
Plasmodium : malaria
Chapter 21
Fungi Invade the Land
A Fungus is Not a Plant
•
The fungi are a distinct kingdom of organisms, comprising about 74,000
species
– mycologists are scientists who study fungi
•
There are many significant differences between fungi and plants, including
– fungi are heterotrophs
– fungi have filamentous bodies
– fungi have nonmotile sperm
– fungi have cell walls made of chitin
– fungi have nuclear mitosis
A Fungus Is Not a Plant
• fungi exist mainly in the form of slender filaments called
hyphae (singular, hypha)
– each hypha is basically a long string of cells
– different hypha can associate with each other to form much
larger structures
– a mass of hyphae is called a mycelium
• the main body of a fungus is not a mushroom but the extensive
network of fine hyphae that penetrate the soil, wood, or flesh in
which the fungus is growing
• the mycelium may contain many meters of hyphae
Masses of hyphae form mycelia
The dense interwoven mat you see here growing through leaves
on a forest floor is a mycelium made up of microscopic hyphae.
A Fungus Is Not a Plant
• Fungal cells can intercommunicate because
fungal cells are separated by incomplete septa
(singular, septum)
– cytoplasm can flow freely among the cells of the
hypha
– many nuclei may be connected together by the
shared cytoplasm
– proteins synthesized throughout the hyphae can be
carried to hyphal tips
– all parts of the fungal body are metabolically active
Figure 21.3 Septum and pore between
cells in a hypha
Reproduction and Nutrition of Fungi
• Fungi reproduce both asexually and
sexually
– all fungal nuclei, except for the zygote, are
haploid
– often in sexual reproduction of fungi, different
“mating types” must participate
• when two hyphae of different mating types come
into contact, the hyphae fuse
Reproduction and Nutrition of Fungi
• Spores are a common means of reproduction among the
fungi
• Spores are well suited to the needs of an organism
anchored to one place
• Spores are small and light and remain suspended in the
air for long periods of time and may be carried great
distances
• When a spore lands in a suitable environment, it
germinates and begins to divide, forming a new fungal
hypha
Many fungi produce spores
Reproduction and Nutrition of Fungi
• All fungi perform external digestion
– they secrete digestive enzymes into their
surroundings and then absorb back into their
bodies any organic molecules
– many fungi are able to break down the
cellulose in wood
– some fungi are carnivores
• for example, the oyster fungus attracts nematode
worms and then feeds upon them
Figure 21.5 The oyster mushroom
Table 21.1 Fungi
Ecological Roles of Fungi
• Fungi, together with bacteria,
are the principal decomposers
in the biosphere
• Fungi are virtually the only
organisms capable of breaking
down lignin in wood
• Fungi, by breaking down
substances, release critical
building blocks from the bodies
of dead organisms and make
them available to other
organisms
Fungi as Parasites
• Cause series plant and
animal diseases
– Examples:
•
•
•
•
Corn smut
Mildew
Wheat rust
Cordyceps
• Cause some human disease
– Athletes foot
– Ringworm
– Thrush
Ecological Roles of Fungi
• Fungi often act as disease-causing organisms
for both plants and animals
Ecological Roles of Fungi
• Fungi have many important commercial
uses
– the manufacture of bread, beer, wine, cheese
and soy sauce all depend on fungi
– many antibiotics are derived from fungi
– some fungi can be used to clean up toxic
substances from the environment
Ecological Roles of Fungi
• Some fungi are edible, others contain
poisonous toxins
Ecological Roles of Fungi
• Fungi are involved in a variety of intimate
symbiotic associations with algae and
plants
– the fungus contributes the ability to absorb
minerals and other nutrients from the
environment
– the photosynthesizer contributes the ability to
use sunlight to power the building of organic
molecules
Ecological Roles of Fungi
• Two kinds of mutualistic associations
between fungi and autotrophic organisms
are ecologically important
– mycorrhizae are symbiotic associations
between fungi and the roots of plants
– lichens are symbiotic associations between
fungi and either green algae or cyanobacteria
Ecological Roles of Fungi
• In most mycorrhizae, the
fungal hyphae actually
penetrate the outer cells of the
plant root and extend far out
into the soil
– these are called
endomycorrhizae
• In some mycorrhizae, the
fungal cells grow between but
do not penetrate the roots
– these are called
ectomycorrhizae
Figure 21.16 Endomycorrhizae and
ectomycorrhizae
Ecological Roles of Fungi
• A lichen is a symbiotic association
between a fungus and a photosynthetic
partner
– most of the visible body of the lichen consists
of its fungus, but interwoven between hyphal
layers are cyanobacteria, green algae, or both
– lichens can invade harsh habitats but are
sensitive to pollutants
Lichens growing on a rock