Transcript early plants 1

Plants
Colonized Land
Land plants evolved from
green algae
 Green algae called charophyceans are
the closest relatives of land plants
Morphological and Biochemical
Evidence
 Land plants share key traits only with
charophyceans:
 Peroxisome enzymes
 Structure of flagellated sperm
 Chlorophyll A
Viridiplantae
Streptophyta
Plantae
Red algae
Chlorophytes
Ancestral alga
Charophyceans
Embryophytes
Derived Traits of Plants
 Five key traits appear in nearly all land
plants but are absent in the green algae:
 Apical meristems
 Alternation of generations
 Walled spores produced in sporangia-aexual
reproduction
 Multicellular gametangia-gamete producing
structures
 Multicellular dependent embryos
Apical Meristems
Apical
Meristem
of shoot
Developing
leaves
Apical meristem
Shoot
100 µm
Root
100 µm
Alternation of Generations
Haploid multicellular
organism (gametophyte)
Mitosis
Mitosis
Gametes
Spores
MEIOSIS
FERTILIZATION
Zygote
Mitosis
Diploid multicellular
organism (sporophyte)
The Origin and Diversification of
Plants
 Fossil evidence indicates that plants were on
land at least 475 million years ago
 Fossilized spores and tissues have been
extracted from 475-million-year-old rocks
Fossilized spores.
Unlike the spores of
most living plants,
which are single
grains, these spores
found in Oman are in
groups of four (left;
one hidden) and two
(right).
Fossilized
sporophyte tissue.
The spores were
embedded in tissue
that appears to be
from plants.
Land plants
Vascular plants
Seed plants
Angiosperms
Gymnosperms
Pterophytes
Seedless vascular plants
Lycophytes
Mosses
Hornworts
Liverworts
Charophyceans
Bryophytes
Origin of seed plants
(about 360 mya)
Origin of vascular plants
(about 420 mya)
Origin of land plants
(about 475 mya)
Ancestral
green alga
The life cycles of mosses and
other bryophytes are dominated
by the gametophyte stage
 Bryophytes are represented today by three
phyla of small herbaceous (nonwoody)
plants:
 Liverworts, phylum Hepatophyta
 Hornworts, phylum Anthocerophyta
 Mosses, phylum Bryophyta
Bryophyte Gametophytes
 In all three bryophyte phyla,
gametophytes are larger and longerliving than sporophytes
 Sporophytes are typically present only
part of the time
Animation: Moss Life Cycle
 Bryophyte gametophytes
 Produce flagellated sperm in antheridia
 Produce ova in archegonia
 Generally form ground-hugging carpets and are
at most only a few cells thick
 Some mosses have conducting tissues in the
center of their “stems” and may grow
vertically
Bryophyte Sporophytes
 Bryophyte sporophytes
 Grow out of archegonia
 Are the smallest and simplest of all extant
plant groups
 Consist of a foot, a seta, and a sporangium
 Hornwort and moss sporophytes have
stomata
MOSS SPOROPHYTE
MOSS GAMETOPHYTE
LE 29-9d
Polytrichum
commune,
hairy cap
moss
Sporophyte
Gametophyte
Walled Spores
Produced in Sporangia
Longitudinal section of
Sphagnum sporangium (LM)
Multicellular
Gametangia
Multicellular,
Dependent Embryos
Archegonium
with egg
Female gametophyte
Spores
Embryo
Maternal
tissue
Sporangium
2 µm
Sporophyte
Gametophyte
Male gametophyte
10 µm
Antheridium
with sperm
Wall
ingrowths
Sporophyte and sporangium
of Sphagnum (a moss)
Archegonia and antheridia
of Marchantia (a liverwort)
Placental
transfer
cell
Raindrop
Key
Male
gametophyte
Haploid (n)
Diploid (2n)
Sperm
“Bud”
Spores develop into
threadlike protonemata.
A sperm swims
through a film of
moisture to an
archegonium and
fertilizes the egg.
Antheridia
Protonemata
The haploid
protonemata
produce “buds”
that grow into
gametophytes.
Most mosses have separate
male and female gametophytes,
with antheridia and archegonia,
respectively.
“Bud”
Egg
Gametophore
Spores
Female
Archegonia
gametophyte
Meiosis occurs and haploid
spores develop in the sporangium
of the sporophyte. When the
sporangium lid pops off, the
peristome “teeth” regulate gradual
release of the spores.
Peristome
The sporophyte grows a
long stalk, or seta, that emerges
from the archegonium.
Sporangium
MEIOSIS
Mature
sporophytes
Rhizoid
Seta
Calyptra
Capsule
(sporangium)
Foot
FERTILIZATION
(within archegonium)
Zygote
Embryo
Archegonium
Young
sporophyte
Capsule with
peristome (SEM)
Female
gametophytes
Attached by its foot, the
sporophyte remains
nutritionally dependent on the
gametophyte.
The diploid zygote
develops into a
sporophyte embryo within
the archegonium.
LIVERWORT STRUCTURE
GEMMA CUPS
LE 29-9a
Gametophore of
female gametophyte
500 µm
Foot
Seta
Sporangium
Marchantia polymorpha,
a “thalloid” liverwort
Marchantia sporophyte (LM)
Ecological and Economic
Importance of Mosses
 Sphagnum, or “peat moss,” forms
extensive deposits of partially decayed
organic material known as peat
 Sphagnum plays an important role in
the Earth’s carbon cycle
LE 29-10
A peat bog.
Gametophyte
Sporangium at
tip of sporophyte
Living
photosynthetic Dead waterstoring cells
cells
100 µm
Closeup of
Sphagnum.
Note the “leafy”
Gametophytes and
their offspring, the
sporophytes.
Sphagnum “leaf” (LM). The
combination of living photosynthetic
cells and dead water-storing cells
gives the moss its spongy quality.
“Tolland Man,” a bog mummy dating from 405–100 B.C. The
acidic, oxygen-poor conditions produced by Sphagnum can
preserve human or animal bodies for thousands of years.
Ferns and other seedless
vascular plants formed the first
forests
 Bryophytes and bryophyte-like plants were the
prevalent vegetation during the first 100 million
years of plant evolution
 Vascular plants began to diversify during the
Carboniferous period
 Vascular plants dominate most landscapes today
Origins and Traits of Vascular
Plants
 Fossils of the forerunners of vascular
plants date back about 420 million
years
 , branching sporophytes
 They lacked other derived These early
tiny plants had independent traits of
vascular plants
Life Cycles with Dominant
Sporophytes
 In contrast with bryophytes,
sporophytes of seedless vascular plants
are the larger generation, as in the
familiar leafy fern
 The gametophytes are tiny plants that
grow on or below the soil surface
Animation: Fern Life Cycle
LE 29-12
Key
Haploid (n)
Diploid (2n)
Spore
Antheridium
Young
gametophyte
MEIOSIS
Sporangium
Sperm
Archegonium
Egg
Sporangium
Mature
sporophyte
New
sporophyte
Zygote
Sorus
Gametophyte
Fiddlehead
FERTILIZATION
Transport in Xylem and Phloem
 Vascular plants have two types of
vascular tissue: xylem and phloem
 Xylem conducts most of the water and
minerals and includes dead cells called
tracheids
 Phloem consists of living cells and
distributes sugars, amino acids, and
other organic products
Evolution of Roots
 Roots are organs that anchor vascular
plants
 They enable vascular plants to absorb
water and nutrients from the soil
 Roots may have evolved from
subterranean stems
Evolution of Leaves
 Leaves are organs that increase the surface
area of vascular plants, thereby capturing
more solar energy that is used for
photosynthesis
 Leaves are categorized by two types:
 Microphylls, leaves with a single vein
 Megaphylls, leaves with a highly branched
vascular system
 According to one model of evolution,
microphylls evolved first, as outgrowths of
stems
LE 29-13
Vascular tissue
Microphylls
Megaphylls
Sporophylls and Spore Variations
 Sporophylls are modified leaves with sporangia
 Most seedless vascular plants are homosporous,
producing one type of spore that develops into a
bisexual gametophyte
 All seed plants and some seedless vascular plants
are heterosporous, having two types of spores
that give rise to male and female gametophytes
Classification of Seedless
Vascular Plants
 There are two phyla of seedless
vascular plants:
 Lycophyta includes club mosses, spike
mosses, and quillworts
 Pterophyta includes ferns, horsetails, and
whisk ferns and their relatives
LE 29-14a
Selaginella apoda,
a spike moss
LE 29-14b
Isoetes
gunnii,
a quillwort
LE 29-14c
Strobili
(clusters of
sporophyllis)
Diphasiastrum tristachyum, a club moss
LE 29-14d
Psilotum
nudum,
a whisk
fern
LE 29-14e
Equisetum
arvense,
field
horsetail
Vegetative stem
Strobilus on
fertile stem
LE 29-14f
Athyrium filix-femina, lady fern
Phylum Pterophyta: Ferns,
Horsetails, and Whisk Ferns
and Relatives
 Ferns are the most diverse seedless
vascular plants, with more than 12,000
species
 They are most diverse in the tropics but
also thrive in temperate forests
 Some species are even adapted to arid
climates
The Significance of Seedless
Vascular Plants
 The ancestors of modern lycophytes, horsetails,
and ferns grew to great heights during the
Carboniferous, forming the first forests
 These forests may have helped produce the
global cooling at the end of the Carboniferous
period
 The decaying plants of these Carboniferous
forests eventually became coal
FERNS VS GYMNOSPERMS
 Ferns vs Gymnosperms
 1. Two types of spores

a. Megaspores-origin of female gametophyte

1. Zygote

2. Embryo-sporophyte

b. Microspores-origin of male gametophytes

1. Pollen tube/pollen

2. Separate gametophytes-Separate sexes

3. Gametophyte much more reduced

a. No chlorophyll/Not free living

4. No flagella on sperm

5. Young embryo house within seed

a. Protects embryo / Embryo self sufficient

b. Nutrients from seed to grow
GYMNOSPERMS-
conifers, cycads, ginkgoes
Name means "naked seed"









A. General characteristics
1. Lack separate gametophyte generation
2. Heterosporous
3. Develop seed-no spreading spores
a. Contains egg that comes from megaspore
b. Contains embryo after fertilization
4. Have pollen
a. Microspore turns into pollen
b. Develops pollen tube to remove the necessity of water
for fertilization-enters thru micropyle of seed
 5. Adaptive importance of pollen and seed











a. Aids in dispersal-wind-water-insects-etc
b. Protects embryonic plant from drying out
c. Protects embryo`s food store from predators or
parasites
d. Food storage analogous to yolk of egg
6. They have no flowers, they have cones
a. Staminate cones-male cones that release pollen
b. Ovulate cones-female cones that produce egg-ovules
B. Development of secondary growth
1. Cell division occurs in regions around periphery
2. Conducting tissues multiplied into cylindrical zone
3. Enables increase in diameter of plant/tree-like height