Download From prokaryotes to eukaryotes

生物學
Lecture 5:
From
prokaryotes
y
to
eukaryotes
生物醫學系
羅時成老師
[email protected]
ext: 3295
Prokaryotes and Eukayrotes
• 學習目標:
• To know differences between cells with
and without nucleus and understand the
endosymbiosis hypothesis
Prokaryotes
y
and Eukaryotes
y
• 1. Three domains of classification---Bacteria,,
Archaea, and Eukaryotes,
• 2.
2 H
How bacteria
b t i cause diseases
di
(Koch’s
(K h’
postulation).
• 3. The beneficial of microorganisms and genetic
engineering.
• 4. How prokaryotes and eukaryotes were coevolved (endosymbiosis
(
i i hypothesis).
i)
Eukarya
Land plants
Green algae
Cellular slime molds
Dinoflagellates
Forams
Ciliates
Red algae
Diatoms
Amoebas
Euglena
Trypanosomes
yp
Leishmania
Animals
Fungi
Green
nonsulfur bacteria
Sulfolobus
Thermophiles
(Mitochondrion)
Spirochetes
Halophiles
COMMON
ANCESTOR
OF ALL
LIFE
Methanobacterium
Archaea
Chlamydia
Green
sulfur
lf bacteria
b t i
Bacteria
Cyanobacteria
(Plastids, including
chloroplasts)
Euryarchaeotes
C
Crenarchaeotes
h
t
UNIVERSAL
ANCESTOR
Nanoarchaeotes
Do
omain Arrchaea
Korarchaeotes
Doma
ain
Eukarrya
Eukaryotes
Proteobacteria
Spirochetes
Cyanobacteria
Gram-positive
Gram
positi e
bacteria
Domain Bacteria
Chlamydias
Figure 21.UN01
Bacteria
Genome
size
Number of
genes
Gene
density
Introns
Other
noncoding
DNA
Archaea
Most are 16 Mb
1,5007,500
Higher than in eukaryotes
None in
protein-coding
t i
di
genes
Present in
some genes
Very little
Eukarya
Most are 104,000 Mb, but a
few are much larger
5,00040,000
Lower than in prokaryotes
(Within eukaryotes, lower
density is correlated with larger
genomes.))
Unicellular eukaryotes:
t but
b t prevalent
l t only
l in
i
present,
some species
Multicellular eukaryotes:
present in most genes
Can be large amounts;
generally more repetitive
noncoding
di DNA iin
multicellular eukaryotes
Table 27.2
(A) Mimivirus (arrows) in cytocentrifuged
y
g A. ppolyphaga
yp g cells, seen as Gram-positive
p
particles about mycoplasma size and appearance
(B) Electron microscopy of
stained mimivirus and U.
urealyticum (a cell)
(C) Phylogenetic tree from
alignment of
ribonucleotide reductase
small subunit sequences
Genome Size
Comparison
Science 341, 226
Acanthamoeba polyphaga, the host
eukaryote
k
cell
ll
●
●
●
Most common protist in soil
Bacterivores
Cause amoebic keratitis and encephalitis
N. Philippe et al. (19 July 2013)
Pandoraviruses: amoeba viruses
with genomes up to 2.5 Mb.
Science 341 (6143 cover), 281
Transmission electron
microscopy of a Pandoravirus
particle (length: 1.2 μm)
Explaination: Despite obeying
all criteria to discriminate
viruses from cells (no ribosomes,
no ATP
A production,
i
no cell
division), these Acanthamoeba
vviruses,
uses, u
unrelated
e ated to p
previously
ev ous y
recognized virus families, have
genomes of up to 2.5 megabases,
and
d more genes (CDS
(CDSs)) th
than
some microsporidia eukaryotic
cells.
Phylogeny of the DNA polymerases hinting at
the existence of 4th domain in the Tree of Life
Endosymbiosis in Eukaryotic
Evolution
• There is now considerable evidence that much protist
diversity has its origins in endosymbiosis
• Endosymbiosis is the process in which a unicellular
organism engulfs another cell, which becomes an
endosymbiont and then organelle in the host cell
• Mitochondria evolved by endosymbiosis of an aerobic
prokaryote
k
t
• Plastids evolved by endosymbiosis of a photosynthetic
cyanobacterium
© 2011 Pearson Education, Inc.
Figure 28.2
Plastid
Dinoflagellates
Membranes
are represented
d k li
lines in
i
as dark
the cell.
Secondary
endosymbiosis
Apicomplexans
Red alga
Cyanobacterium
1 2
3
Primary
endosymbiosis
Heterotrophic
eukaryote
Stramenopiles
Secondary
endosymbiosis
One of these
membranes was
lost in red and
green algal
d
descendants.
d t
Plastid
Euglenids
Secondary
endosymbiosis
Green alga
Chlorarachniophytes
Figure 28.2a
Membranes
are represented
as dark lines in
the cell.
Red alga
C
Cyanobacterium
b t i
1 2
3
Primary
endosymbiosis
Heterotrophic
eukaryote
One off these
O
th
membranes was
lost in red and
green algal
l l
descendants.
Green alga
Figure 28.2b
Plastid
Dinoflagellates
Secondary
endosymbiosis
A i
Apicomplexans
l
Red alga
Stramenopiles
Figure 28.2c
Secondary
endosymbiosis
Plastid
Euglenids
Secondary
endosymbiosis
d
bi i
Green alga
Chlorarachniophytes
• The plastid-bearing
plastid bearing lineage of protists evolved into red
and green algae
• The DNA of plastid genes in red algae and green algae
closely resemble the DNA of cyanobacteria
• On
O severall occasions
i
during
d i eukaryotic
k
ti evolution,
l ti redd
and green algae underwent secondary endosymbiosis,
i which
in
hi h they
th were ingested
i
t d by
b a heterotrophic
h t t hi
eukaryote
© 2011 Pearson Education, Inc.
Five Supergroups of Eukaryotes
• It is no longer thought that amitochondriates (lacking
mitochondria) are the oldest lineage of eukaryotes
• Many have been shown to have mitochondria and have
been reclassified
• Our
O understanding
d t di off the
th relationships
l ti hi among protist
ti t
groups continues to change rapidly
• One hypothesis divides all eukaryotes (including
protists) into five supergroups
© 2011 Pearson Education, Inc.
Diplomonads
Parabasalids
Euglenozoans
Excavata
Figure 28.3a
Apicomplexans
Ciliates
Diatoms
Stramenopilles
Golden algae
Brown algae
Chromalveolata
Alveolates
s
Dinoflagellates
Oomycetes
Forams
Radiolarians
Gre
een
alg
gae
Chlorophytes
Charophytes
Land plants
Archaeplastida
Red algae
Rhizariia
Cercozoans
Gymnamoebas
Entamoebas
Opis
sthokonts
Nucleariids
Fungi
Choanoflagellates
Animals
Unikonta
a
Amo
oebozoans
Slime molds
Craig Venter creates ssynthetic
nthetic life form
• Craig Venter and his team have
b il the
built
h genome off a bacterium
b
i
from scratch and incorporated it
into a cell to make what they call
the world's first synthetic life
form
• O
On May
ay 21,, 2010
0 0
Synthetic Biology
• Mycoplasma laboratorium is a planned partially
synthetic species of bacterium derived from the
genome of Mycoplasma genitalium. This effort in
synthetic biology is being undertaken at the J.
C i Venter
Craig
V
Institute
I i
b a team off approximately
by
i
l
20 scientists headed by Nobel laureate Hamilton
Smith and including DNA researcher Craig
Smith,
Venter and microbiologist Clyde A. Hutchison III.
Mycoplasma genitalium was chosen as it was the
species
i with
i h the
h smallest
ll number
b off genes known
k
at that time.
Dictyostelium
y
discoideum
黏菌
http://www.youtube.com/watch?V=bkVhLJLG7ug
Overview: Masters of Adaptation
• Utah’s
Utah s Great Salt Lake can reach a salt concentration
of 32%
• Its pink color comes from living prokaryotes
© 2011 Pearson Education, Inc.
• Prokaryotes thrive almost everywhere, including
places too acidic, salty, cold, or hot for most other
organisms
• Most prokaryotes are microscopic, but what they lack
in size they make up for in numbers
• There are more in a handful of fertile soil than the
number
b off people
l who
h have
h
ever lived
li d
• Prokaryotes are divided into two domains: bacteria
and archaea
© 2011 Pearson Education, Inc.
Concept: Structural and functional
adaptations contribute to prokaryotic
success
• E
Earth’s
th’ fi
firstt organisms
i
were likely
lik l prokaryotes
k
t
• Most prokaryotes are unicellular, although some
species
i form
f
colonies
l i
• Most prokaryotic cells are 0.5–5 µm, much smaller
th the
than
th 10–100
10 100 µm off many eukaryotic
k
ti cells
ll
• Prokaryotic cells have a variety of shapes
• The three most common shapes are spheres (cocci),
rods (bacilli), and spirals
© 2011 Pearson Education, Inc.
1 m
1 m
3 m
Figure 27.2
((a)) Spherical
p
((b)) Rod-shaped
p
((c)) Spiral
p
Cell-Surface Structures
• An important feature of nearly all prokaryotic cells is
their cell wall, which maintains cell shape, protects
the cell
cell, and prevents it from bursting in a hypotonic
environment
• Eukaryote cell walls are made of cellulose or chitin
• Bacterial cell walls contain peptidoglycan, a network
off sugar polymers
l
cross-linked
li k d bby polypeptides
l
id
© 2011 Pearson Education, Inc.
• Archaea contain polysaccharides and proteins but lack
peptidoglycan
• Scientists use the Gram stain to classify bacteria by
cell wall composition
• Gram-positive
G
iti bacteria
b t i have
h
simpler
i l walls
ll with
ith a
large amount of peptidoglycan
• Gram-negative bacteria have less peptidoglycan and
an outer membrane that can be toxic
© 2011 Pearson Education, Inc.
Figure 27.3
(a) Gram-positive bacteria: peptidoglycan traps crystal violet.
Gram-positive
bacteria
(b) Gram-negative bacteria: crystal violet is easily rinsed
away, revealing red dye.
Gram-negative
bacteria
Carbohydrate portion
of lipopolysaccharide
Cell
wall
Peptidoglycan
layer
Cell
wall
Plasma
membrane
10 m
Outer
membrane
Peptidoglycan
layer
Plasma membrane
• Many antibiotics target peptidoglycan and damage
bacterial cell walls
• Gram-negative
Gram negative bacteria are more likely to be
antibiotic resistant
• A polysaccharide
l
h id or protein
t i layer
l
called
ll d a capsule
l
covers many prokaryotes
© 2011 Pearson Education, Inc.
Figure 27.4
Bacterial
cell wall
Bacterial
capsule
Tonsil
cell
200 nm
• Some prokaryotes have fimbriae,
fimbriae which allow them
to stick to their substrate or other individuals in a
colony
• Pili (or sex pili) are longer than fimbriae and allow
prokaryotes to exchange DNA
© 2011 Pearson Education, Inc.
Figure 27.5
Fimbriae
1 m
Motility
• In a heterogeneous environment,
environment many bacteria
exhibit taxis, the ability to move toward or away from
a stimulus
• Chemotaxis is the movement toward or away from a
chemical stimulus
© 2011 Pearson Education, Inc.
• Most motile bacteria propel themselves by flagella
scattered about the surface or concentrated at one or
both ends
• Flagella of bacteria, archaea, and eukaryotes are
composed of different proteins and likely evolved
independently
© 2011 Pearson Education, Inc.
Figure 27.6
Flagellum
Filament
Hook
Motor
Cell wall
Plasma
as a
membrane
Rod
Peptidoglycan
p
gy
layer
20 nm
Figure 27.6a
20 nm
Hook
Motor
Evolutionary Origins of Bacteria
Flagella
• Bacterial flagella are composed of a motor,
motor hook,
hook
and filament
flagella s proteins are modified versions
• Many of the flagella’s
of proteins that perform other tasks in bacteria
• Flagella likely evolved as existing proteins were
added to an ancestral secretory system
exaptation where existing
• This is an example of exaptation,
structures take on new functions through descent
with modification
© 2011 Pearson Education, Inc.
Internal Organization and DNA
• Prokaryotic cells usually lack complex
compartmentalization
• Some prokaryotes do have specialized membranes
that perform metabolic functions
ese aree usually
usu y infoldings
o d gs of
o thee plasma
p s membrane
e b e
• These
© 2011 Pearson Education, Inc.
Figure 27.7
1 m
0.2 m
Respiratory
membrane
b
Thylakoid
membranes
(a) Aerobic prokaryote
(b) Photosynthetic prokaryote
• The prokaryotic genome has less DNA than the
eukaryotic genome
• Most of the genome consists of a circular
chromosome
• The
Th chromosome
h
is
i nott surrounded
d d by
b a membrane;
b
it
is located in the nucleoid region
• Some species of bacteria also have smaller rings of
DNA called plasmids
© 2011 Pearson Education, Inc.
Figure 27.8
Chromosome
Plasmids
1 m
• There are some differences between prokaryotes and
eukaryotes in DNA replication, transcription, and
translation
• These allow people to use some antibiotics to inhibit
bacterial growth without harming themselves
© 2011 Pearson Education, Inc.
Reproduction and Adaptation
• Prokaryotes reproduce quickly by binary fission and
can divide every 1–3 hours
• Key features of prokaryotic reproduction:
– They are small
– They
h reproduce
d
bby bi
binary fission
fi i
– They have short generation times
© 2011 Pearson Education, Inc.
• Many prokaryotes form metabolically inactive
endospores, which can remain viable in harsh
conditions for centuries
© 2011 Pearson Education, Inc.
Figure 27.9
Endospore
Coat
0.3 m
• Their short generation time allows prokaryotes to
evolve quickly
– For example
example, adaptive evolution in a bacterial
colony was documented in a lab over 8 years
• Prokaryotes are not “primitive”
primitive but are highly
evolved
© 2011 Pearson Education, Inc.
Concept:
p Rapid
p reproduction,
p
,
mutation, and genetic recombination
promote genetic diversity in
prokaryotes
k
t
• Prokaryotes
k
have
h
considerable
id bl genetic
i variation
i i
• Three factors contribute to this genetic diversity:
– Rapid reproduction
– Mutation
utat o
– Genetic recombination
© 2011 Pearson Education, Inc.
Rapid Reproduction and Mutation
• Prokaryotes reproduce by binary fission, and
offspring cells are generally identical
• Mutation rates during binary fission are low,
low but
because of rapid reproduction, mutations can
accumulate rapidly in a population
• High diversity from mutations allows for rapid
evolution
l ti
© 2011 Pearson Education, Inc.
Genetic Recombination
• Genetic recombination,
recombination the combining of DNA from
two sources, contributes to diversity
• Prokaryotic DNA from different individuals can be
brought together by transformation, transduction, and
conjugation
• Movement of genes among individuals from different
species
i is
i called
ll d horizontal
h i t l gene transfer
t
f
© 2011 Pearson Education, Inc.
Transformation and Transduction
• A prokaryotic cell can take up and incorporate foreign
DNA from the surrounding environment in a process
called transformation
• Transduction is the movement of genes between
bacteria by bacteriophages (viruses that infect bacteria)
© 2011 Pearson Education, Inc.
Figure 27.11-4
Phage
A B
Donor cell
A B
A
Recombination
A
A B
A B
Recipient
R
i i t
cell
Recombinant cell
Conjugation and Plasmids
• Conjugation is the process where genetic material is
transferred between prokaryotic cells
• In bacteria
bacteria, the DNA transfer is one way
• A donor cell attaches to a recipient by a pilus, pulls it
closer,
l
andd transfers
t
f DNA
• A piece of DNA called the F factor is required for
the production of pili
© 2011 Pearson Education, Inc.
Figure 27.12
1 m
Sex pilus
The F Factor as a Plasmid
• Cells containing the F plasmid function as DNA
d
donors
dduring
i conjugation
j ti
• Cells without the F factor function as DNA recipients
during conjugation
g conjugation
j g
• The F factor is transferable during
© 2011 Pearson Education, Inc.
Figure 27.13
Bacterial chromosome
F plasmid
F cell
(donor)
F cell
Mating
bridge
F cell
(recipient)
F cell
Bacterial
chromosome
(a) Conjugation and transfer of an F plasmid
Hfr cell
(donor)
A
A
A
F factor
F cell
(recipient)
A
A
A
A
(b) Conjugation and transfer of part of an Hfr bacterial chromosome
A
A
A
Recombinant
F bacterium
The F Factor in the Chromosome
• A cell with the F factor built into its chromosomes
f ti
functions
as a ddonor dduring
i conjugation
j ti
• The recipient becomes a recombinant bacterium, with
DNA from two different cells
© 2011 Pearson Education, Inc.
R Plasmids and Antibiotic Resistance
• R plasmids carry genes for antibiotic resistance
• Antibiotics kill sensitive bacteria, but not bacteria
with specific R plasmids
• Through natural selection, the fraction of bacteria
with genes for resistance increases in a population
exposed to antibiotics
• Antibiotic-resistant strains of bacteria are becomingg
more common
© 2011 Pearson Education, Inc.
Concept : Diverse nutritional and
metabolic adaptations have evolved
in prokaryotes
• Prokaryotes can be categorized by how they obtain
energy and carbon
–
–
–
–
Phototrophs obtain energy from light
Chemotrophs obtain energy from chemicals
Autotrophs require CO2 as a carbon source
Heterotrophs require an organic nutrient to make
organic compounds
© 2011 Pearson Education, Inc.
• Energy and carbon sources are combined to give four
major modes of nutrition:
–
–
–
–
Photoautotrophy
Chemoautotrophy
Ph t h t t h
Photoheterotrophy
Chemoheterotrophy
© 2011 Pearson Education, Inc.
Table 27.1
The Role of Oxygen in Metabolism
• Prokaryotic metabolism varies with respect to O2
– Obligate aerobes require O2 for cellular respiration
– Obligate anaerobes are poisoned by O2 and use
fermentation or anaerobic respiration
– Facultative
F
lt ti anaerobes
b can survive
i with
ith or without
ith t
O2
© 2011 Pearson Education, Inc.
Nitrogen Metabolism
• Nitrogen is essential for the production of amino
acids and nucleic acids
• Prokaryotes can metabolize nitrogen in a variety of
ways
• In
I nitrogen
it
fixation,
fi ti
some prokaryotes
k
t convertt
atmospheric nitrogen (N2) to ammonia (NH3)
© 2011 Pearson Education, Inc.
Metabolic Cooperation
• Cooperation between prokaryotes allows them to use
environmental resources they could not use as
individual cells
• In the cyanobacterium Anabaena, photosynthetic
cells and nitrogen-fixing
nitrogen fixing cells called heterocysts (or
heterocytes) exchange metabolic products
© 2011 Pearson Education, Inc.
Ecological Interactions
• Symbiosis is an ecological relationship in which two
species live in close contact: a larger host and smaller
symbiont
• Prokaryotes often form symbiotic relationships with
larger organisms
© 2011 Pearson Education, Inc.
• In mutualism,
mutualism both symbiotic organisms benefit
• In commensalism, one organism benefits while
neither harmingg nor helping
p g the other in anyy
significant way
• In parasitism, an organism called a parasite harms
b ddoes not kill its
but
i host
h
• Parasites that cause disease are called pathogens
• The ecological communities of hydrothermal vents
depend on chemoautotropic bacteria for energy
© 2011 Pearson Education, Inc.
Concept: Prokaryotes have both beneficial and
harmful impacts on humans
• S
Some prokaryotes
k
are hhuman pathogens,
h
bbut others
h
have positive interactions with humans
© 2011 Pearson Education, Inc.
Mutualistic Bacteria
• Human intestines are home to about 500
500–11,000
000
species of bacteria
• Many of these are mutalists and break down food
that is undigested by our intestines
• Probiotics
i i are microorganisms
i
i
that
h provide
id
health benefits when consumed
• Prebiotics is a general term to refer to
chemicals that induce the growth and/or
activity of commensal microorganisms (e.g.,
b t i andd fungi)
bacteria
f
i) that
th t contribute
t ib t to
t
© 2011 Pearson Education, Inc.
microbiota
• Human beings have clusters of bacteria in
different parts of the body, such as in the
p layers
y of skin (skin
(
surface or deep
microbiota), the mouth (oral microbiota),
the vagina (vaginal microbiota)
microbiota), and so on.
on
GUT MICROBIOTA
• Gut microbiota (formerly called gut flora) is the
name given today to the microbe population living
in our intestine. It contains tens of trillions of
microorganisms, including at least 1000 different
species
i off known
k
bacteria
b
i with
i h more than
h 3
million genes (150 times more than human genes).
Microbiota can,
can in total,
total weigh up to 2 kg.
kg One
third of our gut microbiota is common to most
people, while two thirds are specific to each one of
us. In
I other
h words,
d the
h microbiota
i bi in
i your intestine
i
i
is like an individual identity card.
Pathogenic Bacteria
• Prokaryotes cause about half of all human
diseases
– For example
example, Lyme disease is caused by a
bacterium and carried by ticks (15,000 to
20,000 people infected)
– Two million people die in Mycobacterium
tuberculosis and another 2 million die from
diarrheal caused by various bacteria
© 2011 Pearson Education, Inc.
• Pathogenic prokaryotes typically cause disease by
releasing exotoxins or endotoxins
• Exotoxins are secreted and cause disease even if the
prokaryotes that produce them are not present
Cholera
o e toxin,
o , causes
c uses diarrheal
d
e disease
d se se too stimulate
s u e
• C
intestine cells to release chloride ions.
• Endotoxins are released onlyy when bacteria die and
their cell walls break down
• Horizontal ggene transfer: O157:H7 ((1387 ggenes not
found in the 5416 genes of K12 .
© 2011 Pearson Education, Inc.
• Horizontal gene transfer can spread genes associated
with virulence
• Some pathogenic bacteria are potential weapons of
bioterrorism
© 2011 Pearson Education, Inc.
Prokaryotes in Research and
Technology
• Experiments using prokaryotes have led to important
advances in DNA technology
– For example, E. coli is used in gene cloning
– For example, Agrobacterium tumefaciens is used to
produce transgenic
p
g
plants
p
• Bacteria can now be used to make natural plastics
© 2011 Pearson Education, Inc.
• Prokaryotes are the principal agents in
bioremediation, the use of organisms to remove
pollutants from the environment
• Bacteria can be engineered to produce vitamins,
antibiotics and hormones
antibiotics,
• Bacteria are also being engineered to produce ethanol
f
from
waste
t biomass
bi
© 2011 Pearson Education, Inc.
Figure 27.21
(a)
(c)
(b)
Robert Koch (11 December 1843
– 27 May 1910)
Koch’s postulations
•
•
•
•
The microorganism must be found in abundance in all
organisms
g
sufferingg from the disease,, but should not be
found in healthy organisms.
The microorganism must be isolated from a diseased
organism and grown in pure culture.
culture
The cultured microorganism should cause disease when
introduced into a healthy organism.
The microorganism must be reisolated from the
inoculated, diseased experimental host and identified as
beingg identical to the original
g
specific
p
causative agent.
g
Koch’ss postulates for the 21st
Koch
century:
• A nucleic
l i acid
id sequence
belonging to a putative pathogen
should be present in most cases of
an infectious disease. Microbial
nucleic acids should be found
preferentially in those organs or
gross anatomic sites known to be
diseased, and not in those organs
that lack pathology.
p
gy
Koch’ss postulates for the 21st
Koch
century:
• Fewer, or no, copies of pathogen-associated
nucleic acid sequences should occur in
hosts or tissues without disease.
• With resolution of disease,
disease the copy number
of pathogen-associated nucleic acid
sequences should decrease or become
undetectable. With clinical relapse, the
opposite should occur.
Koch’ss postulates for the 21st
Koch
century:
• When sequence detection predates disease, or
sequence copy number correlates with severity of
disease or pathology, the sequence-disease
association is more likely to be a causal
relationship.
• The nature of the microorganism inferred from the
available sequence should be consistent with the
known biological
g
characteristics of that group
g p of
organisms.
Koch’ss postulates for the 21st
Koch
century:
• Tissue-sequence correlates should be sought at the
cellular level: efforts should be made to
demonstrate specific in situ hybridization of
microbial sequence to areas of tissue pathology
andd to visible
i ibl microorganisms
i
i
or to areas where
h
microorganisms are presumed to be located.
• These sequence
sequence-based
based forms of evidence for
microbial causation should be reproducible
Detection of bacteria- or virus-infection
Immunology method
S
Serum—serology
l
(
(sero-typing)
yp g)
Immuno-diffusion
RIA radio immunoassay
RIA—radio-immunoassay
EIA (ELISA)
Nucleic acid method
Hybridization
PCR or RT-PCR
S
Sequencing
i
Figure 28.6
9 m

Figure 31.1
Figure 31.22
Figure 31.27
Staphylococcus
Penicillium
Zone of
inhibited
growth
Figure 30.2
PLANT GROUP
Mosses and other
nonvascular plants
Gametophyte Dominant
Sporophyte
Ferns and other seedless
vascular plants
Seed plants (gymnosperms and angiosperms)
Reduced, independent
(photosynthetic and
free-living)
Reduced (usually microscopic), dependent on surrounding
sporophyte tissue for nutrition
Reduced, dependent on
Dominant
gametophyte for nutrition
Dominant
Gymnosperm
Sporophyte
(2n)
Sporophyte
(2n)
Microscopic female
gametophytes (n) inside
ovulate cone
Gametophyte
(n)
Angiosperm
Microscopic
female
gametophytes
(n) inside
these parts
of flowers
Example
Gametophyte
(n)
Microscopic male
gametophytes (n)
i id pollen
inside
ll
cone
Sporophyte (2n)
Microscopic
male
gametophytes
(n) inside
parts
these p
of flowers
Sporophyte (2n)
Figure 32.11
Ct
Ctenophora
h
Eumeta
azoa
Me
etazoa
ANCESTRAL
COLONIAL
FLAGELLATE
Porifera
Cnidaria
Acoela
Bilateria
Chordata
Platyhelminthes
L
Lophotro
ochozoa
a Ecdysozoa
Deute
erostomiia
Echinodermata
Rotifera
Ectoprocta
Brachiopoda
Mollusca
Annelida
Nematoda
Arthropoda