Eukaryotic cells arose around 1.5 billion years ago
Figures 15.18
Internal membranes in eukaryotes
may have resulted from infolding of
the cell membrane.
Section 15.3
© McGraw Hill, LLC
Figures 15.1
1
Endosymbiosis explains the origin of mitochondria and
chloroplasts
Evidence shows that aerobic bacteria, and later
photosynthetic cyanobacteria, took up residence inside
ancient host cells.
Section 15.3
© McGraw Hill, LLC
Figure 15.19
2
Endosymbiosis is a potent force in
evolution
Some eukaryotes have
chloroplasts with three
or four membranes,
resulting from
multiple endosymbiosis
events.
(b): Michael Abbey/Science Source
Section 15.3
© McGraw Hill, LLC
Figure 15.20
3
Multicellularity evolved from
unicellular organisms
Multicellularity was a critical step leading to the evolution of
plants, animals, and fungi. Each kingdom arose from
different lineages of multicellular protists.
Individual cells joining
and taking on
specialized roles
(slime molds)
or
single-cells dividing
and sticking together
then expressing
different subsets in
DNA?
This single-celled green alga called
Chlamydomonas shares many similarities with
its close relative, the many-celled Volvox.
Figure 15.21
15.3 Mastering Concepts
List a logical sequence of
evolutionary events that starts
with a prokaryote and ends
with a multicellular eukaryote.
Answer: Prokaryote develops an
inner membrane network resulting in
the formation of the nucleus. The
eukaryote acquires organelles via
endosymbiosis. The eukaryotes
group with others, dividing the
functions among them. Alternatively
the eukaryote divides but does not
separate from its sister cell.
© McGraw Hill, LLC
Ilya Sviridenko/Shutterstock
5
Protists are the simplest eukaryotes
Classifying protists is
difficult, since they are
not a single clade. It is
not clear if they are a true
kingdom.
Originally, protists were
defined as eukaryotes
that are not plants, fungi,
or animals.
As new DNA data
becomes available,
protists are being
reclassified into dozens
of new groups.
Section 15.4
Figure 15.22
Photo: ©Melba/age fotostock RF
Protists are organized into three groups
Biologists traditionally
classify protists in terms
of the kingdom they most
closely resemble:
• Algae - resemble plant
cells
• Slime molds/water
molds - resemble
fungal cells
• Protozoa - resemble
animal cells
Photo: MELBA PHOTO AGENCY/Alamy Stock Photo
Section 15.4
© McGraw Hill, LLC
Figure 15.22
7
Algae are photosynthetic protists
Algae live in water and carry out photosynthesis.
They produce much of the O2 in Earth’s atmosphere and
support food webs in oceans, lakes, rivers, and ponds as
plankton.
Cells contain
chloroplast with
yellow, gold,
brown, red and
green pigments.
Live among
threads of fungi
(lichens).
(algal bloom): ©Michael Marten/Science Source
Dinoflagellates are protists with flagella & cellulose plates
• Dinoflagellates are
characterized by two
flagella. They use them to
whirl around in the ocean.
• Some are photosynthetic;
some live inside animals
such as jellyfish; some
are bioluminescent.
• They can overgrow and
produce toxins, causing
red tides. (if eat shellfish
David M. Phillips/Science Source
Section 15.4
© McGraw Hill, LLC
during red tide can be
poisoned).
Figure 15.23
9
Diatoms are algae with unique silica cell walls
(diatoms): Jan Hinsch/Science Source; (inset): Steve Gschmeissner/Science Source
Most diatoms live in oceans, where they are a crucial source of
photosynthesis and food for zooplankton. Their cell walls are very
intricate and give them unique shapes.
Section 15.4
© McGraw Hill, LLC
Figure 15.24
10
Diatoms are algae with unique silica cell walls
• Excess diatoms die and sink to the sea floor and become a
biological carbon pump
• In addition diatoms, which sank to the bottom of oceans along
with other microscopic photoautotrophs millions of years ago,
are thought to be the primary source of the crude oil and gas
we pump from the earth today
• Deposits of diatoms, called diatomaceous earth, are used in
many different ways including filtering water, as a polish due to
its mild abrasive properties and as a mechanical insecticide to
name a few.
Brown algae are the most complex and largest protists
• These multicellular
algae live in marine
habitats all over the
world.
• The kelps shown here
produce enormous
underwater forests
that provide food and
habitat for many
animals.
Ralph A. Clevenger/Getty Images
Section 15.4
© McGraw Hill, LLC
Figure 15.25
12
Red algae
• Red algae range in size from microscopic, unicellular
protists to large, multicellular forms, “seaweed”
• Play an important role in many coral reefs
• Commercially valuable:
• Carageenan (stabilizer for ice cream,
pudding, etc.)
• Used to wrap sushi
• Source of agar & agarose
Figures 15.26, 15.27
Red and green algae share many
features with plants
Green algae use the same photosynthetic pigments as plants.
Their habitats and body forms are diverse; they may be
unicellular, filamentous, colonial, or multicellular.
Volvox
Chlamydomonas
Figures 15.26, 15.27
Some heterotrophic protists were once classified as fungi
• Slime molds and
water molds have
filamentous feeding
structures that are
outwardly similar to
fungi.
• However, they are
only distantly related
to fungi in terms of
DNA sequence.
Section 15.4
© McGraw Hill, LLC
©W.E. Fry, Plant Pathology, Cornell University
Water mold
(white
threads)
decomposing a
goldfish
Figure 15.28
15
Slime molds are protists that can switch between two
lifestyles
• Slime molds live in
damp habitats and
feed by
decomposing
microbes.
• They are unusual
because they can
exist as single cells
or as large masses
that behave like a
multicellular
organism (slug).
Section 15.4
© McGraw Hill, LLC
Photos: (slug): Carolina Biological Supply Company/Phototake;
(fruiting body): David Scharf/Science Source
Figure 15.29
16
Protozoa are diverse heterotrophic protists
Protozoa are grouped together based on morphology and
locomotion but are only distantly related to each other in terms of
DNA sequence.
Figure 15.31a
Figure 15.32
Eye of Science/Science Source
Nancy Nehring/Getty Images
Peter Parks/OceansImage/Photoshot/Newscom
Section 15.4
© McGraw Hill, LLC
Figure 15.30b
17
Flagellated protozoa are motile
Flagellated protozoa have one or more flagella, which they
use to move around.
They live in soil, oceans, and fresh water.
Some are parasites that live in our bodies.
(a): Eric V. Grave/Science Source; (b, c): Eye of Science/Science Source
Section 15.4
© McGraw Hill, LLC
Figure 15.30
18
Flagellated protists
• Examples include:
• heterotrophic termite endosymbionts,
• autotrophic species,
• mixotrophs such as Euglena,
• the common waterborne parasite Giardia intestinalis,
• the parasite Trichomonas vaginalis, which causes 5
million new infections each year of human reproductive
tracts, and
• the parasite Trypanosoma, which causes sleeping
sickness in humans.
• Trypanosoma brucei, the causative agent of sleeping sickness, spends part of its life cycle in
the tsetse fly and part in humans. (credit: modification of work by CDC)
Amoeboid protozoa produce pseudopodia
Figure 15.31a
Amoeboid protozoa produce
extensions known as pseudopodia,
which are important in locomotion
and capturing food.
Peter Parks/Oceans-Image/Photoshot/Newscom
MELBA PHOTO AGENCY/Alamy Stock Photo
Section 15.4
© McGraw Hill, LLC
Figure 15.22
21
Foraminiferans
• Includes many of the amoebas, most of which have threadlike or
needle-like pseudopodia
• Foraminiferans are unicellular heterotrophic protists occasionally
resembling tiny snails
• Foraminiferans have porous shells, called tests that are built from
various organic materials and typically hardened with calcium
carbonate
• Tests may house photosynthetic algae which can be harvested
for nutrition
• Pseudopodia extend through the test pores and allow
foraminiferans to move, feed, and gather additional
building materials
© McGraw Hill, LLC
Radiolarians
• Radiolarians exhibit intricate exteriors of glassy silica
• Needle-like pseudopods supported by microtubules
radiate outward from the cell bodies of these protists
• The shells of dead radiolarians sink to the ocean floor,
where they may accumulate in 100 meter-thick depths
© McGraw Hill, LLC
Ciliates are complex protozoa
Ciliates are unicellular protozoa
characterized by abundant
hairlike cilia, which propel the
organism and sweep food into
the cell.
• Paramecium includes protists
that have organized their cilia
into a plate-like primitive
mouth, called an oral groove,
which is used to capture and
digest bacteria
• Paramecium also uses
contractile vacuoles, which
are osmoregulatory vesicles
that fill with water as it enters
the cell by osmosis and then
contract to squeeze water
from the cell.
• Figure 15.32
Contractile
vacuoles
Nucleus
Figure 15.31
(a): ©Peter Parks/Oceans-Image/Photoshot/Newscom; (b): ©Eric V. Grave/Science Source
Apicomplexans are nonmotile
parasites
These protists live in animals and cause a number of diseases.
For example, an apicomplexan called Plasmodium causes
malaria. Toxoplasma (cat feces).
People with one copy of
the sickle cell allele are
much less likely to contract
malaria than are people
with two dominant alleles.
• Section 15.4
Figure 7.15
Protist habitats
• Nearly all protists exist in some type of aquatic
environment
• Freshwater
• Marine
• Damp soil
• Snow
• Several protist species are parasites that infect animals or
plants
• A few protist species live on dead organisms or their
wastes, and contribute to their decay.
Ecology of Protists
• As primary producers, protists feed a large proportion of the
world’s aquatic species
• One-quarter of the world’s photosynthesis is due to protists
• Protist parasites cause malaria, African sleeping sickness, and
waterborne gastroenteritis in humans
• Other protist pathogens prey on plants, effecting massive
destruction of food crops (downy and powdery mildews)
• An oomycete protist caused the well-known Irish potato famine
in the nineteenth century that claimed the lives of approximately
1 million people and led to the emigration of at least 1 million
more from Ireland
• Saprobic protists have the essential function of returning
inorganic nutrients to the soil and water.
15.4 Mastering Concepts
What features define the
protists?
Answer: Protists are eukaryotes that
are not plants, fungi, or animals.
Ilya Sviridenko/Shutterstock
© McGraw Hill, LLC
28
Fungi are essential decomposers
Fungi are more closely related to animals
than plants.
Although outwardly they may look like
plants, they share many chemical and
metabolic features with animals.
Fungi are the planet’s
garbage processors.
They break down dead
plants and animals,
releasing nutrients to
be recycled.
Section15.5
Figure 15.33
©Corbis RF
Fungi are a diverse group that share a
unique set of features
Fungi are heterotrophs
with external digestion.
Their cell walls are
composed primarily of
chitin.
Their storage
carbohydrate is glycogen,
the same as for animals.
Most are multicellular,
although some are
unicellular.
Figure 15.33
Fungi are made of hyphae and fruiting
bodies
The fruiting body above
ground produces spores,
which are microscopic
reproductive cells.
Figure 15.34
A network of underground filaments called
hyphae absorb nutrients. Collectively the
hyphae are called the mycelium.
Fungal classification is based on reproductive structures
Each fungus
phylum makes a
different type of
spore for sexual
reproduction.
Section 15.5
© McGraw Hill, LLC
Figure 15.33
32
Fungi have unique reproductive cycles
• Unlike plants and
animals, fungi spend
most of their lives in
the haploid stage.
• The diploid stage
may be very brief.
Section 15.5
© McGraw Hill, LLC
Figure 15.35
33
Asexual Reproduction
• Asexual reproduction is ideal for rapid spread
• No need to find a mate
• No fruiting body
• No meiosis
• Many fungi produce conidia
• Asexual spores grown at the tips of hyphae
• Unicellular yeasts reproduce by budding
Asexual Fungi
• Imperfect fungi use only asexual reproduction for spore production;
they include many species commonly called molds and yeasts.
• A mold is any rapidly growing fungus that reproduces asexually
by producing spores.
• Yeast refers to any single-celled fungus.
• Often responsible for food spoilage, allergies, and disease
• Medically important fungi that reproduce primarily by asexual means
include
• Athlete’s foot fungus (Epidermophyton floccosum)
• Infectious yeast (Candida albicans)
Sporangia grow at the end of stalks,
which appear as (a) white fuzz seen on
this bread mold, Rhizopus stolonifer.
The (b) tips of bread mold are the
spore-containing sporangia.
• Structure of fruiting bodies varies in ways that reflect
adaptations for spore dispersal
• Some fruiting bodies are edible (e.g., truffles, morels)
and may be cultivated for human consumption
Distinctive growth processes
• Mycelia can grow quickly when food is plentiful
• Hyphae extend tips through substrate
• Narrow dimensions/extensive branching provide high surface
area for absorption
• Importance of osmosis and cytoplasmic streaming
• Entry of water provides force for tip extension
• Enzymes and cell wall materials are carried to tip by vesicles
Fungi interact with other organisms
Many fungi secrete enzymes that break down dead plants
and animals, releasing inorganic nutrients for recycling.
This is crucial for many ecosystems.
Photo: Fotosr52/Shutterstock
Section 15.5
© McGraw Hill, LLC
Julie Dermansky/Science Source
Figure 15.37a
40
We use fungi for food and medicine
Basidiomycetes and
ascomycetes give food
delicious flavors.
Yeasts are used to produce
wine and beer.
Ascomycetes are famous for
secreting the antibiotics
penicillin and cyclosporine.
Staphylococcus
aureus (bacteria)
Penicillium (mold)
Zone of
inhibited
growth
• Figure 15.37b&c
Some fungi are pathogenic
• Plants and animals can
die from fungal
diseases.
• Certain infectious fungi
cause illnesses in
humans, including
pneumonia, ringworm,
and athlete’s foot.
(a, leaf): Nigel Cattlin/Alamy Stock Photo; (a, inset): Scenics & Science/Alamy
Stock Photo; (b): Morley Read/Alamy Stock Photo; (c, bat): Greg
Turner/Pennsylvania Game Commission/USGS; (c, inset): ©Deborah J. Springer
Section 15.5
© McGraw Hill, LLC
Figure 15.38
42
Parasitic fungi harm plants and animals
• Of the 100,000 known species of fungi, about 30% are either
parasites or pathogens in or on plants.
• About 80% of plant diseases are caused by fungi.
• Between 10% and 50% of the world’s fruit harvest is lost
each year to fungal attack.
• A variety of fungi, including smuts and rusts, infect grain
crops.
Ergots
Corn smut
Ergot of rye
Parasitic fungi harm plants and animals
• Only about 50 species of fungi is parasitic on animals.
• Fungal diseases of the skin include
• ringworm, named because it appears as circular red areas on
the skin,
• athlete’s foot, also caused by the ringworm fungus,
• vaginal yeast infections, and
• deadly lung diseases that produce tuberculosis-like symptoms
in the lungs.
Endophytes live inside plant tissues
These fungi do not trigger disease symptoms or otherwise
harm plants.
Some produce substances that help defend plants against
herbivores. All plants harbor endophytes.
(a): Biophoto Associates/Science Source; (b, root tips): Wim van Egmond/Science Photo Library; (b, cross section): Biology Pics/Science Source
Section 15.5
© McGraw Hill, LLC
Figure 15.39
45
Fungi and plants form mycorrhizae
Mycorrhizae are structures that allow plants and fungi to share
materials with each other.
Fungi absorb water and minerals while the plant produces
carbohydrates in photosynthesis  Symbiotic relationship
(a): Biophoto Associates/Science Source; (b, root tips): Wim van Egmond/Science Photo Library; (b, cross section): Biology Pics/Science Source
Section 15.5
© McGraw Hill, LLC
Figure 15.39
46
Lichens are dual organisms
Lichens are fungi with green algae or cyanobacteria living among their
hyphae. Symbiotic Relationship
The fungi absorb minerals and water while the algal cells produce sugars
by photosynthesis.
Photos: (a): ©iStockphoto.com/seraficus; (b, inset): Eye of Science/Science Source
Section 15.5
© McGraw Hill, LLC
Figure 15.40
47
15.5 Mastering Concepts
How do scientists classify the
five phyla of fungi? What
characteristics do all fungi
share?
Answer: The five phyla
(chytridiomycetes, zygomycetes,
glomeromycetes, ascomycetes
basidiomycetes) are based on the
presence and types of sexual
structures. All fungi are eukaryotic,
extra cellular heterotrophs, have cell
walls made of chitin, and store
carbohydrates as glycogen.
© McGraw Hill, LLC
Ilya Sviridenko/Shutterstock
48
Investigating Life: Algae release light when they are
disturbed
If you ever visit a coastline
where bioluminescent algae
live, drop a pebble in the
water. You’ll see sparkles of
light from the protists you
disturbed.
Ilya Sviridenko/Shutterstock
© McGraw Hill, LLC
49
Investigating Life: Algae are disturbed by copepods
• The light is emitted
by dinoflagellates
when herbivores
called copepods are
trying to eat them.
• Luckily for the
dinoflagellates there
are fish called
sticklebacks that eat
copepods.
Figure 15.Aa
© McGraw Hill, LLC
50
Investigating Life: Algae call predator fish for help
Copepods that eat
bioluminescent
dinoflagellates face a
higher risk of being eaten
by sticklebacks than
copepods given only
nonbioluminescent
dinoflagellates to eat.
Figure 15.Ab
© McGraw Hill, LLC
51