Download Figure 26.1

Chapter 26
The Tree of Life
An Introduction to
Biological Diversity
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: Changing Life on a Changing Earth
• Life is a continuum
– Extending from the earliest organisms to the
great variety of species that exist today
– Life had dramatic effect on the Earth, and
these changes subsequently affected the
evolution of species
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• Geological events that alter environments
– Change the course of biological evolution
• Conversely, life changes the planet that it
inhabits
Figure 26.1
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• Geologic history and biological history have
been episodic
– Marked by what were in essence revolutions
that opened many new ways of life
– Changing oxygen levels, evolution of plants,
evolution of animals
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• Concept 26.1: Conditions on early Earth made
the origin of life possible
• Most biologists now think that it is at least a
credible hypothesis
– That chemical and physical processes on early Earth
produced very simple cells through a sequence of
stages
• According to one hypothetical scenario
– There were four main stages in this process
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1. Synthesis of small precursor molecules
2. Formation of larger polymer molecules
3. Packaging of polymers into protobionts
4. Origin of self-replicating molecules (RNA and
DNA) that hold instructions for an organism
NOTE: much of this is speculative and cannot be
absolutely validated, but can be scientifically
tested in the laboratory and field
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Synthesis of Organic Compounds on Early Earth
• Earth formed about 4.6 billion years ago
– Along with the rest of the solar system
• Earth’s early atmosphere
– Contained water vapor and many chemicals
released by volcanic eruptions
– Nitrogen, nitrogen oxides, carbon dioxide,
methane, ammonia, hydrogen, hydrogen
sulfide
– NOTE: very little oxygen in early atmosphere!
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• Oparin and Haldane (1920’s)
– early organic compounds formed with energy
from lightning and UV radiation from the sun
(little ozone)
– Earth had a “reducing” environment
• Miller and Urey (1953) – experiment showed
that small molecules could be produced
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• Laboratory experiments simulating an early
Earth atmosphere
– Have produced organic molecules from inorganic
precursors, but the existence of such an atmosphere
on early Earth is unlikely
EXPERIMENT
Miller and Urey set up a closed system in their
laboratory to simulate conditions thought to have existed on early
Earth. A warmed flask of water simulated the primeval sea. The
strongly reducing “atmosphere” in the system consisted of H2,
methane (CH4), ammonia (NH3), and water vapor. Sparks were
discharged in the synthetic atmosphere to mimic lightning. A
condenser cooled the atmosphere, raining water and any dissolved
compounds into the miniature sea.
Water vapor
Cold
water
As material circulated through the apparatus,
Miller and Urey periodically collected samples for analysis. They
identified a variety of organic molecules, including amino acids such
as alanine and glutamic acid that are common in the proteins of
organisms. They also found many other amino acids and complex,
oily hydrocarbons.
Organic molecules, a first step in the origin of
life, can form in a strongly reducing atmosphere.
Figure 26.2
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Electrode
Condenser
RESULTS
CONCLUSION
CH4
H2O
Cooled water
containing
organic
molecules
Sample for
chemical analysis
• Instead of forming in the atmosphere
– The first organic compounds on Earth may have been
synthesized near submerged volcanoes and deepsea vents
Figure 26.3
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Extraterrestrial Sources of Organic Compounds
• Some of the organic compounds from which
the first life on Earth arose
– May have come from space
• Carbon compounds
– Have been found in some of the meteorites
that have landed on Earth
• Amino acids
– Have been found on a 4.5 billion year old
chodrites contain l and d forms of amino acids
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Looking Outside Earth for Clues About the Origin of Life
• The possibility that life is not restricted to Earth
– Is becoming more accessible to scientific
testing
• Mars shows signs of water in the past
– Which would be conducive to life formation
• Europa (a Jupiter moon)
– Also shows signs of ocean water underneath
the surface, where life may also exist
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Abiotic Synthesis of Polymers
• Small organic molecules
– Polymerize when they are concentrated on hot
sand, clay, or rock
– No enzymes or ribozymes are required
– May have served as catalysts for other
reactions to occur
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Protobionts
• Protobionts
– Are aggregates of abiotically produced molecules
surrounded by a membrane or membrane-like
structure
– Show simple reproduction and metabolism
– Maintain an internal chemical environment
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• Laboratory experiments demonstrate that
protobionts
– Could have formed spontaneously from abiotically
produced organic compounds
• For example, small membrane-bounded
droplets called liposomes
– Can form when lipids or other organic molecules are
added to water
– Can form membrane voltage
– Can selectively take up compounds from environment
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Glucose-phosphate
20 m
Glucose-phosphate
Phosphorylase
Starch
Amylase
Phosphate
Maltose
Maltose
(a) Simple reproduction. This liposome is “giving birth” to smaller
liposomes (LM).
(b) Simple metabolism. If enzymes—in this case,
phosphorylase and amylase—are included in the
solution from which the droplets self-assemble,
some liposomes can carry out simple metabolic
reactions and export the products.
Figure 26.4a, b
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The “RNA World” and the Dawn of Natural Selection
• The first genetic material
– Was probably RNA, not DNA
– It can store genetic information and act as an
enzyme when in three-dimensional form
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• RNA molecules called ribozymes have been
found to catalyze many different reactions,
including
– Self-splicing
– Making complementary copies of short stretches of
their own sequence or other short pieces of RNA
– Act on other RNA’s to make them functional
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Ribozyme capable of replicating RNA
Ribozyme
(RNA molecule)
3
Template
Nucleotides
Figure 26.5
Complementary RNA copy
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5
5
• RNA molecules could have “evolved” in the
classic sense of Natural Selection
– Show both a genotype and phenotype
– New variants arise through mutation
– Could have been early genetic material for the
first “protobionts”
– Could have been the template upon which
more stable DNA molecules were built
– Transition from RNA world to DNA world
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• Early protobionts with self-replicating, catalytic
RNA
– Would have been more effective at using
resources and would have increased in
number through natural selection
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• Concept 26.2: The fossil record chronicles life
on Earth
• Careful study of fossils
– Opens a window into the lives of organisms
that existed long ago and provides information
about the evolution of life over billions of years
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How Rocks and Fossils Are Dated
• Sedimentary strata
– Reveal the relative ages of fossils
– Strata in different areas can be compared
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• Index fossils
– Are similar fossils found in the same strata in different
locations
– Allow strata at one location to be correlated with strata
at another location
Figure 26.6
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• The absolute ages of fossils
– Can be determined by radiometric dating
Ratio of parent isotope
to daughter isotope
– Half-life of an isotope such as C-14 (5,730 years)
Accumulating
“daughter”
isotope
12
Remaining
“parent”
isotope
1
Figure 26.7
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14
18
2
Time (half-lives)
3
1 16
4
• The magnetism of rocks
– Can also provide dating information
• Magnetic reversals of the north and south
magnetic poles
– Have occurred repeatedly in the past
– Leave their record on rocks throughout the world
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The Geologic Record
• By studying rocks and fossils at many different
sites
– Geologists have established a geologic record of
Earth’s history
1. eons (Archean, Proterozoic, Phanerozoic)
2. eras (Paleozoic, Mesozoic, Cenozoic)
3. periods (Cambrian….Permian…..Jurassic)
4. epochs (Paleocene….Pliocene)
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• Many of these time periods
– Mark major changes in the composition of
fossil species
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Mass Extinctions
• The fossil record chronicles a number of
occasions
– When global environmental changes were so rapid
and disruptive that a majority of species were swept
away
Millions of years ago
600
400
500
300
200
100
0
2,500
100
Number of
taxonomic
Permian mass families
extinction
80
2,000
Extinction rate (
60
1,500
40
1,000
Cretaceous
mass extinction
Number of families (
)
Extinction rate
)
500
20
Paleozoic
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Mesozoic
Paleogene
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Ordovician
Silurian
Cambrian
Proterozoic eon
Figure 26.8
Cenozoic
Neogene
0
0
• Two major mass extinctions, the Permian and
the Cretaceous
– Have received the most attention
• The Permian extinction
– Claimed about 96% of marine animal species and 8
out of 27 orders of insects
– Is thought to have been caused by enormous volcanic
eruptions
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• The Cretaceous extinction
– Doomed many marine and terrestrial organisms, most
notably the dinosaurs
– Is thought to have been caused by the impact of a
large meteor in the area of current Yucatan
NORTH
AMERICA
Yucatán
Peninsula
Chicxulub
crater
Figure 26.9
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• Much remains to be learned about the causes
of mass extinctions
– But it is clear that they provided life with
unparalleled opportunities for adaptive
radiations into newly vacated ecological niches
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• The analogy of a clock
– Can be used to place major events in the Earth’s
history in the context of the geological record
Cenozoic
Humans
Land plants
Origin of solar
system and
Earth
Animals
4
1
Proterozoic Archaean
Eon
Eon
Billions of years ago
2
3
Multicellular
eukaryotes
Figure 26.10
Single-celled
eukaryotes
Prokaryotes
Atmospheric
oxygen
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• Concept 26.3: As prokaryotes evolved, they
exploited and changed young Earth
• The oldest known fossils are stromatolites
– Rocklike structures composed of many layers of
bacteria and sediment
– Which date back 3.5 billion years ago
– Currently found in warm, shallow, salty, bays
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(a) Lynn Margulis (top right), of the University of Massachussetts, and
Kenneth Nealson, of the University of Southern California, are
shown collecting bacterial mats in a Baja California lagoon. The
mats are produced by colonies of bacteria that live in environments
inhospitable to most other life. A section through a mat (inset)
shows layers of sediment that adhere to the sticky bacteria as
the bacteria migrate upward.
(b) Some bacterial mats form rocklike structures called stromatolites,
such as these in Shark Bay, Western Australia. The Shark Bay
stromatolites began forming about 3,000 years ago. The inset
shows a section through a fossilized stromatolite that is about
Figure 26.11a, b 3.5 billion years old.
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The First Prokaryotes
• Prokaryotes were Earth’s sole inhabitants
– From 3.5 to about 2 billion years ago
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Electron Transport Systems
• Electron transport systems of a variety of types
– Evolved more than 3 billion years ago
– Were essential to early life
– Have some aspects that possibly precede life
itself
– Common to photosynthesis and cellular
respiration pathways seen today (Bio 6)
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Photosynthesis and the Oxygen Revolution
• The earliest types of photosynthesis
– Did not produce oxygen by splitting water
– Cyanobacteria – only current bacteria that generate O
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• Oxygenic photosynthesis
– Probably evolved about 3.5 billion years ago in
cyanobacteria
– Can be osbserved in Iron-Oxide deposits (red below)
Figure 26.12
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• When oxygen began to accumulate in the
atmosphere about 2.7 billion years ago
– It posed a challenge for life; many species died
– Some species survived in anaerobic areas
– It provided an opportunity to gain abundant energy
from light
– It provided organisms an opportunity to exploit new
ecosystems
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• Concept 26.4: Eukaryotic cells arose from
symbioses and genetic exchanges between
prokaryotes
• Among the most fundamental questions in
biology is:
– How did complex eukaryotic cells evolve from
much simpler prokaryotic cells?????
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The First Eukaryotes
• The oldest fossils of eukaryotic cells
– Date back 2.1 billion years
– Cholesterol only synthesized by eukaryotes
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Endosymbiotic Origin of Mitochondria and Plastids
• The theory of endosymbiosis
– Proposes that mitochondria and plastids were formerly
small prokaryotes living within larger host cells
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• The prokaryotic ancestors of mitochondria and
plastids
– Probably gained entry to the host cell as undigested
prey or internal parasites
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Cytoplasm
DNA
Plasma
membrane
Ancestral
prokaryote
Infolding of
plasma membrane
Nucleus
Endoplasmic
reticulum
Nuclear envelope
Engulfing
of aerobic
heterotrophic
prokaryote
Cell with nucleus
and endomembrane
system
Mitochondrion
Mitochondrion
Engulfing of
photosynthetic
prokaryote in
some cells
Ancestral
heterotrophic
eukaryote
Figure 26.13
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Plastid
Ancestral
Photosynthetic
eukaryote
• In the process of becoming more
interdependent
– The host and endosymbionts would have
become a single organism
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• The evidence supporting an endosymbiotic
origin of mitochondria and plastids includes
– Similarities in inner membrane structures and
functions
– Both have their own circular DNA
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Eukaryotic Cells as Genetic Chimeras
• Additional endosymbiotic events and horizontal
gene transfers
– May have contributed to the large genomes and
complex cellular structures of eukaryotic cells
– Genetic annealing – gene transfers between bacteria
and archean lineages
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• Some investigators have speculated that
eukaryotic flagella and cilia
– Evolved from symbiotic bacteria, based on symbiotic
relationships between some bacteria and protozoans
50 m
Figure 26.14
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• Concept 26.5: Multicellularity evolved several
times in eukaryotes
• After the first eukaryotes evolved
– A great range of unicellular forms evolved
– Multicellular forms evolved also
– Includes: algae, fungi, plants, animals
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The Earliest Multicellular Eukaryotes
• Molecular clocks
– Date the common ancestor of multicellular
eukaryotes to 1.5 billion years
• The oldest known fossils of eukaryotes
– Are of relatively small algae that lived about
1.2 billion years ago
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• Larger organisms do not appear in the fossil
record
– Until several hundred million years later
• Chinese paleontologists recently described
570-million-year-old fossils
– That are probably animal embryos
Figure 26.15a, b
(a) Two-cell stage
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150 m
(b) Later stage 200 m
• Snowball Earth Hypothesis
– 750-570 mya was a major ice age
– Land masses and seas covered in ice
– Life confined to deep sea vents and hot
springs
– Eventually, Earth began to thaw
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The Colonial Connection
• The first multicellular organisms were colonies
– Collections of autonomously replicating cells
Figure 26.16
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10 m
• Some cells in the colonies
– Became specialized for different functions
• The first cellular specializations
– Had already appeared in the prokaryotic world
• Nostoc differentiate into nitrogen-fixing and
photosynthetic cells
• Eukaryotes develop different cells from a single
egg or zygote
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The “Cambrian Explosion”
• Most of the major phyla of animals
– Appear suddenly in the fossil record that was laid
down during the first 20 million years of the Cambrian
period
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• Phyla of two animal phyla, Cnidaria
(anenomes) and Porifera (sponges)
Early
Paleozoic
era
(Cambrian
period)
Millions of years ago
542
Late
Proterozoic
eon
Figure 26.17
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Arthropods
Molluscs
Annelids
Brachiopods
Chordates
Echinoderms
Cnidarians
500
Sponges
– Are somewhat older, dating from the late Proterozoic
• Molecular evidence
– Suggests that many other animal phyla originated
and began to diverge much earlier, between 1 billion
and 700 million years ago
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Colonization of Land by Plants, Fungi, and Animals
• Cyanobacteria and some procaryotes emerged on
land over 1 billion years ago
• Plants, fungi, and animals
– Colonized land about 500 million years ago
– Had to adapt to less water; cuticles on plants
– Plants evolved form the green algae
– Plants and fungi may have emerged on land together
– Earliest animals were arthropods and vertebrates
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• Symbiotic relationships between plants and
fungi
– Are common today and date from this time
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Continental Drift
• Earth’s continents are not fixed
– They drift across our planet’s surface on great plates of
crust that float on the hot underlying mantle
– This change in land mass distribution had dramatic
effects on the evolution of species in different parts of
the world
– Changing landforms caused extinctions and new forms
of life to emerge
– Similar species found in Ghana and Brazil
– Marsupials became isolated in Australia
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• Often, these plates slide along the boundary of
other plates
– Pulling apart or pushing against each other
Eurasian Plate
North
American
Plate
Juan de Fuca
Plate
Caribbean
Plate
Philippine
Plate
Arabian
Plate
Indian
Plate
Cocos Plate
Pacific
Plate
Nazca
Plate
South
American
Plate
Scotia Plate
Figure 26.18
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African
Plate
Australian
Plate
Antarctic
Plate
• Many important geological processes
– Occur at plate boundaries or at weak points in
the plates themselves
Volcanoes and
volcanic islands
Oceanic ridge
Trench
Figure 26.19
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• The formation of the supercontinent Pangaea
during the late Paleozoic era
India collided with
Eurasia just 10 million
years ago, forming the
Himalayas, the tallest
and youngest of Earth’s
major mountain
ranges. The continents
continue to drift.
0
Cenozoic
– And its breakup during
the Mesozoic era explain
many biogeographic puzzles
Eurasia
65.5
Africa
South
America
Laurasia
135
Mesozoic
Millions of years ago
Antarctica
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Paleozoic
251
Figure 26.20
India
Madagascar
By the end of the
Mesozoic, Laurasia
and Gondwana
separated into the
present-day continents.
By the mid-Mesozoic,
Pangaea split into
northern (Laurasia)
and southern
(Gondwana)
landmasses.
At the end of the
Paleozoic, all of
Earth’s landmasses
were joined in the
supercontinent
Pangaea.
• Concept 26.6: New information has revised
our understanding of the tree of life
• Molecular Data
– Have provided new insights in recent decades
regarding the deepest branches of the tree of life
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Previous Taxonomic Systems
• Early classification systems had two kingdoms
– Plants and animals
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• Robert Whittaker proposed a system with five
kingdoms
– Monera, Protista, Plantae, Fungi, and Animalia
Plantae
Fungi
Protista
Figure 26.21
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Monera
Animalia
Reconstructing the Tree of Life: A Work in Progress
• A three domain system
– Has replaced the five kingdom system
– Includes the domains Archaea, Bacteria, and
Eukarya
– Each domain has been split by taxonomists
into many kingdoms
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Figure 26.22
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Domain Archaea
Domain Bacteria
Universal ancestor
Domain Eukarya
Charophyceans
Chlorophytes
Red algae
Cercozoans, radiolarians
Stramenopiles (water molds, diatoms, golden algae, brown algae)
Chapter 27
Alveolates (dinoflagellates, apicomplexans, ciliates)
Euglenozoans
Diplomonads, parabasalids
Euryarchaeotes, crenarchaeotes, nanoarchaeotes
Korarchaeotes
Gram-positive bacteria
Cyanobacteria
Spirochetes
Chlamydias
Proteobacteria
One current view of biological diversity
Chapter 28
Figure 26.21
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Plants
Fungi
Animals
Bilaterally symmetrical animals (annelids,
arthropods, molluscs, echinoderms, vertebrates)
Cnidarians (jellies, coral)
Chapter 32
Sponges
Chapter 31
Choanoflagellates
Club fungi
Sac fungi
Chapter 28
Arbuscular mycorrhizal fungi
Zygote fungi
Chytrids
Chapter 30
Amoebozoans (amoebas, slime molds)
Angiosperms
Gymnosperms
Seedless vascular plants (ferns)
Bryophytes (mosses, liverworts, hornworts)
Chapter 29
Chapters 33, 34