Transcript Plant Diversity How Plants Colonized Land

Plant Diversity I
How Plants Colonized Land
(The Seedless Plants)
Packet #33
Chapter #29
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Introduction


There are more than
290,000 species of
plants that inhabit the
earth.
How, and why, based
on the theory of
evolution, did plants
venture out of the sea
and onto dry land?
◦ Charophyceans
 Green algae
 Provides some of those
answers
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Information About Plants
Multicellular
 Eukaryotic
 Photoautotrophs
 Cell walls made of cellulose
 Chlorophylls a & b are present in land
plants

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Diversion of Algae and Land Plants

Embryophytes (plants
with embryos) is the
traditional scheme
and equates with
Kingdom Plante
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Similarities Between Charophyceans & Land Plants
EVIDENCE THAT
PLANTS MOVED TO
LAND
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Morphological & Biochemical
Evidence
It is thought that land plants evolved from green algae
 Four Key Traits that “suggest” an evolutionary relationship
between Charophyceans and Land Plants

◦ Homologous peroxisomes
 Both groups contain enzymes that minimize the loss of organic products
due to photorespiration
◦ Formation of phragomoplast
 Synthesis of cell plates during cell division involves the formation of
phragomoplast
◦ Homologous Sperm
 Many plants (gymnosperms) have flagellated sperm that match
charophycean sperm
◦ Homologous cellulose cell walls
 Cell walls of both land plants and charophyceans contain 20-26%
cellulose
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Genetic Evidence

Key nuclear genes
◦ Ribosomal RNA
◦ Cytoskeleton proteins
 In agreement with the biochemical and morphological data

Homologous chloroplasts
◦ Algal plastids, of green algae and algal groups such as
euglenoids, are similar to those found in land plants

Chloroplast DNA found in charophyceans, green
algae, is most closely related to that found in land
plants.
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Adaptations Enabling the Move to
Land

Charophyceans have a
layer of a durable
polymer called
sporopollenin.
◦ Prevents exposed
zygotes from drying out.
◦ May be the precursor to
the tough sporopollenin
walls that encase plant
spores.
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“EVOLUTIONARY”
ADAPTATIONS TO
TERRESTRIAL
LIVING/DERIVED TRAITS
FOR TERRESTRIAL LIVING
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Evolutionary Adaptations to
Terrestrial Living

There are four main
groups of land plants
◦
◦
◦
◦
Bryophytes
Pteridophytes
Gymnosperms
Angiosperms
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Adaptations II

The colonization of land by plants
required the evolution of many
anatomical, physiological and reproductive
adaptations
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Adaptations III

Waxy Cuticle
◦ Used to protect against water loss

Stomata
◦ Gas exchange needed for photosynthesis
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Adaptations IV

Plant Life Cycles
◦ Alternation of Generation
 Part of the life cycle is in a
haploid gametophyte
generation and part in a
diploid sporophyte generation.
 The gametophyte plant
produces gametes via
mitosis
 During fertilization the
gametes fuse together to
form the zygote
 The zygote is the first
stage of the sporophyte
generation.
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Adaptations IV
 Zygote develops into a
multicellular embryo that
the gametophyte protects
and nourishes
 Mature sporophyte plant
develops from the embryo
 Sporogenous cells (spore
mother cells) are produced
 Cells undergo meiosis to
form spores
 The spore is the first
stage of the gametophyte
generation.
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Adaptations V

Most plants produce
multicellular gametangia
◦ Protective jacket of sterile
cells surrounding gametes.
 Gametophyte generation
(More to come later) all
produce their gametes within
multicellular structures
 Gametangia
 Male Gametangium
 Antheridium
 Many sperm
released into the
environment when
mature
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Adaptations V
 Female
Gametangium
 Archegonium
 Produces a
single egg cell
and retains
the egg within
the organism
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Adaptations VI

Production of Secondary Compounds
◦ Plants produce many unique compounds as
byproducts of primary metabolic pathways.
◦ Byproducts help plant defend itself against
herbivores
◦ Compounds have bitter tastes, strong odors
or toxic effects.
◦ Compounds include terpenes, alkaloids and
tannins.
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Adaptations VII
Mosses and ferns, although adapted to life
on land, have motile sperm cells that
require water as a transport medium for
fertilization.
 Ferns, and vascular plants, that “evolved”
at a later time, have xylem, to conduct
water, and phloem, to conduct dissolved
sugar.

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Features That Distinguish Bryophytes From Green Algae and
Other Plants
THE BRYOPHYTES
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Bryophytes

Have several adaptations that green algae
lack
◦ Cuticle
◦ Stomata
◦ Multi cellular gametangia
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Bryophytes II
Non-vascular plants
 Lack xylem
 Lack pholem
 Only plants with a dominant gametophyte
generation.

◦ Sporophytes remain permanently attached
and nutritionally dependent on the
gametophyte.
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Phyla of Pryophytes
BRYOPHYTES
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Bryophyte Diversity
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Phylum Bryophyta
The Mosses

Have gametophytes
that are green plants
that grow from a
filamentous protonema.
◦ Green filamentous
growth that arises from
spore germination in
liverworts and mosses
and eventually gives rise
to a mature
gametophyte.
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Phylum Bryophyta
The Mosses

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Gametophyte bears archegonia
and/or antheridia at the top of
the plant.
During fertilization, sperm cell
fuses with an egg cell in the
archegonium
Zygote grows into an embryo
that develops into a moss
sporophyte which is attached to
the gametophyte.
Meiosis occurs within the capsule
if the sporophyte to produce
spores.
Spores are dispersed by wind.
Spore germinates. Grows into a
protonema that forms a bud.
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Gametophyte
Sporangium
Life Cycle of the Mosses
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Sporangium
Mature Sporangium
Life Cycle of the Mosses
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Germination
Gametophyte
Life Cycle of the Mosses
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Phylum Bryophyta
The Mosses
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
Bryophytes have been
distributed around the
world from the tropics
to the arctic.
They can exist in dry or
cold habitats
◦ They can practically
desiccate
◦ Rehydrates following rain
events.

One wetland moss,
Sphagnum, forms
extensive deposits of
peat.
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Phylum Hepaticophyta
The Liverworts

Have gametophytes
that are flattened,
lobelike thalli.
◦ Plant body, not
differentiated into
roots, stems and
leaves, of some algae,
fungi and similar
simple plantlike
organisms.

Others are leafy
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Phylum Anthocerotophyta
Hornworts

Have thalloid
gametophytes
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Features That Distinguish Ferns and Other Seedless Vascular
Plants From Algae and Bryophytes.
FERNS
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Ferns I

Comparison to
Bryophytes
◦ Ferns have vascular
tissue
◦ Ferns have a dominant
sporophyte generation.
◦ As in bryophytes,
reproduction in ferns
depends on water as a
transport medium for
their motile sperm cells.
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SEEDLESS VASCULAR
PLANTS
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Introduction I
Represent the modern groups that
formed the forest during the evolutionary
time period—The Carboniferous Period.
 Organisms left relics, fossils and coals
 Seed plants were present during this
evolutionary time period but were not
dominant.
 Became important as the swamps dried
up and the global climate cooled.

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Introduction II

There are four phyla of seedless vascular
plants.
◦ Phylum Polypodiophyta
 Ferns
◦ Phylum Psilotophyta
 Whisk ferns
◦ Phylum Equisetophyta
 Horsetail
◦ Phylum Lycophyta
 Club Mosses
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Phylum Pterophyta
Subphylum Polypoiophyta
The Ferns
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Largest and most
diverse group of
seedless vascular
plants.
More than 12,000
species have been
described.
Almost all species are
homosporous (details to
come)
All have megaphylls.
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Phylum Pterophyta
Subphylum Polypoiophyta
The Ferns
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Sprophytes have roots,
rhizomes and leaves that are
megaphylls.
Leaves, or fronds, bear
sporangia in clusters called
sori.
Meiosis of sporangia produces
haploid spores.
Fern gametophyte, called a
prothallus, develops from a
haploid spore and bears both
archegonia and antheridia.
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Keywords

Homospory
◦ The production of one
kind of spore
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



Bryophytes
Whisk ferns
Horsetails
Most club mosses
Most ferns
◦ Spore gives rise to
gametophyte plants
that produce both egg
and sperm cells.
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Keywords II

Heterospory
◦ Production of two kinds of
spores
 Microspores
 Give rise to male gametophytes
that produce sperm cells
 Megaspores
 Give rise to female
gametophytes that produce eggs.
◦ Occurs in
 Certain club mosses
 Certain ferns
 ALL SEED PLANTS.
◦ The “evolution” of
heterospory was an essential
step in the evolution of
seeds.
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Phylum Pterophyta
Subphylum Psilotophyta
The Whisk Ferns
Lack true roots and
leaves
 Consists of
dichotomously
branching rhizomes
 Have erect stems.
 Homosporous
sporophylls.

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Phylum Pterophyta
Subphylum Equisetophyta
The Horsetails
 Sporophytes have
roots
 Rhizomes
 Aerial stems
◦ Hollow and jointed

Leaves that are
reduced megaphylls
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Phylum Lycophyta
The Club Mosses
Consist of roots
 Rhizomes
 Erect branches
 Leaves that are
microphylls.

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