Hypotheses about the origin of life. which is your favorite hypothesis and why

– Evidence of the presence of early prokaryote life. Non-fossil and fossil records.

– Origin of the first eukaryotic cell. Evidence and fossil records. How do the three domains of life appeared and how are they related to each other. Endosymbiosis.

-Diversification of eukaryotic cells. Mention all the supergroups, examples, and wich of the supergroups will evolve in animals, fungi,and plants.

-Appearance and evolution of plants. Conquest of the land by plants.

-Mention of geological change, level of oxygen and CO2, fossil records, and other biological events as reported in the track the History of Life website. Demonstrate integration of these events in the narrative, for example, evolutive interrelations among different groups.

*Formal coherence, and originality.

*Bibliography

*Use the Earth viewer(cite it when you use it), power points, compendium, E-textbook.

*any data must be cited correctly.

Plants & The Conquest Of Land I

Kingdom Plantae evolved within the Archeaplastida Supergroup
Common Eukaryote ancestor

Supergroup Archaeplastida
Land plants and their relatives

Cell walls: rose-shaped complexes are used for cellulose synthesis
Plasmodesmata (channel for communications between cells) are present
Formation of a phragmoplast (forms during plant cytokinesis to allow the formation of the new cell wall separating the two daughter cells)
Sexual reproduction and structure of flagellated sperm
Peroxisome enzymes (that minimize loss of carbohydrates due to photorespiration)
4

Complex charophytes share several derived traits with land plants

New in true plants:

Alternation of generations
Multicellular, dependent Embryo
Walled spores produced in sporangia
Apical meristems

Although present in other green algae (chlorophytes), it was no present in charophycens, the closest relatives to plants.

It seems that alternation of generations appeared during the evolution from ancestor charophyceans to plants, beginning with a delay of meiosis
Alternation of generations

Key traits that appear in nearly all land plants but are absent in the charophytes (charophycean) include

Alternation of generations
Multicellular, dependent embryos
Walled spores produced in sporangia
Apical meristems

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Alternation of generations
Gametophyte
(n)
Mitosis
n
n
n
Spore
Gamete
Gamete from
another plant
Mitosis
n
MEIOSIS
FERTILIZATION
Zygote
2n
Sporophyte
(2n)
Mitosis
Haploid (n)
Diploid (2n)

Figure 26.6-1 Exploring alternation of generations (part 1: cycle)

© 2016 Pearson Education, Inc.
Multicellular, dependent embryos: give name embryophytes
Embryo
Maternal
tissue
Wall ingrowths
10 µm
2 µm
Placental transfer
cell (blue outline)
Embryo (LM) and placental transfer cell (TEM)
of Marchantia (a liverwort)
10 mm
2 mm

Figure 26.6-2 Exploring alternation of generations (part 2: multicellular, dependent embryos)

10
Embryo: a critical innovation
Absent from charophyceans
First distinctive trait acquired by land plants
Embryophytes a synonym for plants
3 features:
Multicellular and diploid
Zygotes and embryos retained
Depends on organic and mineral materials supplied by mother plant – placental transfer tissues

Spores are also present in some protists and in fungi, but plants spores are produced in a specific structure, the plant sporangia, and are covered by sporopollenin, a durable organic material that forms a wall and provides resistance to harsh conditions.
Walled spores produced in sporangia

Meristems are sites of repeated cell division of unspecialized cells. These cells differentiate, and become specialized in relation to the function they will perform.

Apical Meristems are the site of primary growth in a plant, and can be found at the root and shoot tips. Here you can find unspecialized cells, which undergo the following sequence to become a functional part of the plant
Apical meristems

Additional derived traits include:

Cuticle, a waxy covering of the epidermis that functions in preventing water loss and microbial attack
Stomata, specialized pores that allow the exchange of CO2 and O2 between the outside air and the plant
Other innovations appear later in plant evolution and are not present in all plants: Vascular tissue, seeds, pollen, flowers and fruits

Ancestral species gave rise to a vast diversity of modern plants

Figure 26.18-2 Highlights of plant evolution (part 2: art)

Bryophytes, first plants to appear

Bryophytes are anchored to the substrate by rhizoids
The flagellated sperm produced by bryophytes must swim through a film of water to reach and fertilize the egg
In bryophytes, the gametophytes are larger and longer-living than sporophytes. We say that gametophyte is the dominant generation
The height of gametophytes is constrained by lack of vascular tissues

© 2016 Pearson Education, Inc.
Capsule
Seta
Sporophyte
(a sturdy
plant that
takes months
to grow)
Gametophyte
(b) Polytrichum
commune, a moss
(a) Plagiochila deltoidea,
a liverwort
Sporophyte
Gametophyte
(c) Anthoceros sp., a hornwort

The dominant generation, is haploid

Figure 26.19 Bryophytes (nonvascular plants)

LE 29-8
Male
gametophyte
“Bud”
Spores develop into
threadlike protonemata.
Protonemata
“Bud”

The haploid protonemata produce “buds” that grow into gametophytes.
Raindrop
Sperm
Antheridia
Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively.

Egg
Haploid (n)
Diploid (2n)
Key
A sperm swims through a film of moisture to an archegonium and fertilizes the egg.

Archegonia
Rhizoid
Female
gametophyte

Gametophore
Spores
Sporangium
Peristome
MEIOSIS
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.
The sporophyte grows a long stalk, or seta, that emerges from the archegonium.

FERTILIZATION
(within archegonium)
Archegonium
Zygote
Embryo

Calyptra

Young
sporophyte

Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte.
The diploid zygote develops into a sporophyte embryo within the archegonium.

Capsule
(sporangium)
Seta
Foot

Mature
sporophytes
Capsule with
peristome (SEM)
Female
gametophytes
Moss Life Cycle

Vascular Plants or Tracheophytes.
The presence of vascular tissue gives name to this group.
Vascular tissue: complex conducting tissue found in vascular plants. Compound by xylem and phloem
Xylem: Dead cells conducting water and minerals
Phloem: Living cells conducting nutrients derived from photosynthesis (sugar, sap: sugar-rich water solution).

Vascular plants generally possess stems, roots, and leaves having vascular tissues.

Stems: Contain vascular tissue (phloem and xylem) and lignin and produce leaves and reproductive structures
Roots: Specialized for uptake of water and minerals from the soil
Leaves: Photosynthetic function, and conservation of water.

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Microphyll leaves
Microphylls
Unbranched
vascular tissue
Selaginella kraussiana
(Krauss’s spikemoss)
Megaphyll leaves
Megaphylls
Branched
vascular
tissue
Hymenophyllum
tunbrigense
(Tunbridge filmy fern)

Figure 26.22 Microphyll and megaphyll leaves

© 2016 Pearson Education, Inc.
Liverworts
Origin of plants
ANCESTRAL
GREEN ALGA
Mosses
Hornworts
Lycophytes (club mosses,
spikemosses, quillworts)
Monilophytes (ferns,
horsetails, whisk ferns)
Gymnosperms
Origin of seed plants
Angiosperms
500
(bryophytes)
plants
Nonvascular
Vascular plants
plants
Seed
plants
vascular
Seedless
Plants
Origin of vascular plants
450
400
350
300
Millions of years ago (mya)
50
0

Ancestral species gave rise to a vast diversity of modern plants

Figure 26.18 Highlights of plant evolution

Seedless Vascular Plants
Bryophytes were the prevalent vegetation during the first 100 million years of plant evolution
The earliest vascular plants date to 425 million years ago
© 2016 Pearson Education, Inc.

The First Plants to Grow Tall

Seedless vascular plants can be divided into two clades
Lycophytes
(club mosses and their relatives)

Monilophytes
(ferns and their relatives)

Figure 26.20 Lycophytes and monilophytes (seedless vascular plants)

1 m

Key
Haploid (n)
Diploid (2n)
MEIOSIS
Spore
dispersal
Spore
(n)
Young
gametophyte
Rhizoid
Underside
of mature
gametophyte
(n)
Antheridium
Sperm
Archegonium
Egg
FERTILIZATION
Zygote
(2n)
Gametophyte
New
sporophyte
Mature
sporophyte
(2n)
Fiddlehead (young leaf)
Sporangium
Sorus
Sporangium

The life cycle of a fern

24
Figure 29.13 The life cycle of a fern.

© 2016 Pearson Education, Inc.
PLANT GROUP
Mosses and other
nonvascular plants
Gametophyte
Reduced, dependent
on gametophyte for
nutrition
Ferns and other
seedless
vascular plants
Reduced, independent
(photosynthetic and
free-living)
Dominant
Seed plants (gymnosperms and angiosperms)
Reduced (usually microscopic), dependent on
surrounding sporophyte tissue for nutrition
Sporophyte
Dominant
Gymnosperm
Microscopic female
gametophytes (n) inside
ovulate cone
Angiosperm
Microscopic female
gametophytes
(n) inside these parts
of flowers
Microscopic
male
gametophytes
(n) inside
these parts
of flowers
Sporophyte
(2n)
Sporophyte
(2n)
Gametophyte
(n)
Example
Gametophyte
(n)
Microscopic
male
gametophytes (n)
inside pollen
cone
Sporophyte
(2n)
Sporophyte
(2n)
Dominant

pollen

Figure 26.21 Gametophyte-sporophyte relationships in different plant groups

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Plants & The Conquest Of Land II

Ancestral species gave rise to a vast diversity of modern plants

Figure 26.18-2 Highlights of plant evolution (part 2: art)

Extensive forests dominated by tree-sized lycophytes, pteridophytes, and early lignophytes occurred in widespread swampy regions during the warm, moist Carboniferous period (354–290 million years ago)

Ecological effects of vascular plants
First appear 420-429 mya – Coal Age
Carboniferous plants converted huge amounts of atmospheric CO2 into decay-resistant organic material
Removal of large amounts of the greenhouse gas CO2 from the atmosphere by plants had a cooling effect on the climate. Also became drier because cold air holds less moisture than warm air.

Carboniferous proliferation of vascular plants was correlated with a dramatic decrease in CO2 in the atmosphere. It reached the lowest known levels about 290 mya. During this period of very low CO2, atmospheric oxygen levels rose to the highest known levels.

Plants Evolution

Bryophytes produce decay-resistant body tissues. Could have begun process to reduce amount of greenhouse gas CO2 in the atmosphere. Helped to enrich the soils.
Extensive forests dominated by tree-sized lycophytes, pteridophytes, and early lignophytes in widespread swampy regions during the warm, moist Carboniferous period (354–290 mya). They had the effect of cooling and dry the climate. These gave an advantage to seed plants.
65 mya, the K/T event marking end of Cretaceous and beginning of Tertiary. Huge amounts of ash, smoke and haze
dimmed sunlight long enough to kill many of the world’s plants
Dinosaurs were also doomed. Surviving flowering plants diversified. Today Angiosperms Angiosperms represent approximately 80 % of all the known green plants now living.

Transition from seedless vascular plants to seed vascular plants:
Lignin
Wood
Heterospory
Seed
from the Upper Devonian to Lower Carboniferous (383 to 323 million years ago)

Reproductive innovations in seed plants

Reduced Gametophytes

Seed Plants Cell Cycle

. Most seed plants, adult sporophytes develop two different kinds of sporangia: microsporangia & megasporangia (instead of only one type of sporangia)
Megasporangia (2n) produce megaspores(n) by meiosis.
Megaspores (n) undergo mitosis & produce female gametophytes (n) (mega-gametophytes)

The mega-gametophytes (n) remain within the tissues of the ovule and produce one or more egg cells (n) in the archegonium

An ovule consists of a megasporangium surrounded by one or two layers of tissue called integuments.
Microsporangia (2n) produce microspores (n) by meiosis
Microspores (n) undergo mitosis & develop into pollen grains (n), which are the young male gametophytes

Seed plants produce heterospores

Male gametophytes develop from small microspores
Microspores develop into pollen grains, which consist of a male gametophyte enclosed within the protective pollen wall
Pollination is the transfer of pollen to reproductive organs of the plant.
Pollen eliminates the need for a film of water and can be dispersed great distances by air or animals
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Winged pollen from pine
Pollen: the male gametophyte in seed plants

© 2016 Pearson Education, Inc.
Immature
ovulate cone
Integument (2n)
Megaspore (n)
Spore wall
Female
gametophyte (n)
Egg nucleus (n)
Discharged
sperm nucleus (n)
Pollen tube(n)
Seed coat
Spore wall
Food
Supply (n)
Embryo (2n)
Megasporangium(2n)
Micropyle
Pollen grain (n)
Male
gametophyte
(a) Unfertilized ovule
(b) Fertilized ovule
(c) Gymnosperm seed

After fertilization, ovules develop into seeds. Mature seeds are ready for dispersal of the diploid generation and contain:
embryonic sporophyte (2n)
stored food
protective coat

Figure 26.23-s3 From ovule to seed in a gymnosperm (step 3)

The Evolutionary Advantage of Seeds
A seed develops from the whole ovule
A seed is a sporophyte embryo, along with its food supply, packaged in a protective coat
Seeds provide some evolutionary advantages over spores:
Seeds are multicellular; spores are usually single-celled
They may remain dormant from days to years, until conditions are favorable for germination
Seeds have a supply of stored food

Extant seed plants are divided into two clades:

Gymnosperms have “naked” seeds that are not enclosed in chambers
Angiosperms have seeds that develop inside chambers (vessels) called ovaries
Angiosperms also have flowers and fruits
Double fertilization and endosperm
Ovaries that develops in fruits
© 2016 Pearson Education, Inc.
Sperms: Greek for seeds
Gymno: Greek for unclothed, naked
Angio: Greek for vessel

flowers
ovaries- fruits
seed with endosperm

Wood, ovules, seeds, pollen, euphylls

14
14

Ovule

Microsporangium
Megaspore
Egg (n)
Archegonium (n)
Pollen grain (n)
Megasporangium (2n)
Female gametophyte (n)
Integument
Male gametophyte (n)
Embryo (2n)
Sperm
Seed
Seedling
Seed
coat
Ovule
Microspores
Haploid
Diploid
KE
Y
Scale

Fertilization
Ovule
cone
Mature
sporophyte
(2n)
Pollen
cone
Section
of cone
Mitosis
Scale
Cone
scale

Meiosis
Mitosis
Megasporangium
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Pine life cycle
Gymnosperms

Flowers
The flower is an angiosperm structure specialized for sexual reproduction
Many species are pollinated by insects or other animals, while some species are wind-pollinated
A flower is a specialized shoot with up to four types of modified leaves called floral organs
Sepals, which enclose the flower
Petals, which are brightly colored and attract pollinators
Stamens, which produce pollen
Carpels, which produce ovules

Angiosperms

Carpel anatomy
(The term pistil can be used to refer to a single carpel or two or more fused carpels)
Stigma – receives and recognizes pollen
Only appropriate pollen will be allowed to germinate
Style – connects stigma with ovary
Ovary – pollen tube delivers sperm to ovule
Ovaries develop into fruits
Stamen anatomy
Anther – sac called an anther where the pollen is produced
Filament- sustain (stalk)

Diploid cell produces 4 megaspores by meiosis (3 die) and one is left.
Surviving megaspore generate female gametophyte by mitosis.
Female gametophyte consists of 7 cells, one of which is the egg cell

Doble fertilization

Pollen grains (immature male gametophytes) from the stamen are dispersed by the wind or transported by pollinators to the stigma of a flower.
Pollen germinates and delivers two sperms to the female gametophytes by means of a long pollen tube, that is enclosed, fed and guided by the style. Once the sperms reach an ovule in the ovary double fertilization occurs. Double fertilization involves two events:
True fertilization: one sperm nucleus fuses with the egg to produce a diploid zygote that develops later into a young sporophyte
Triple fusion: the other sperm nucleus fuses with the two nucleus of the central cell, generating the first cell of the nutritive endosperm tissue
Double fertilization and therefore endosperm are present in angiosperms, but not in gymnosperms.
Both are derived traits of angiosperms and the presence of endosperm is considered a critical innovation in angiosperms because provide a more efficient food storage to the seed.

20
Fruits
Develop from ovary walls
Aid the dispersal of enclosed seeds
Dispersal prevents competition and aids in colonization
Fruits may be adapted to
Attract animals to eat them, wind dispersal, attach to animal fur or float in water

21
Coevolution
Process by which two or more species of organisms influence each other’s evolutionary pathway
Explains the diverse forms of most flowers and many fruits, and how plants accomplish effective pollen and seed dispersal

In plants:
Pollination coevolution
Seed dispersal coevolution

22
Pollination coevolution
Pollinators foster genetic variability and plant potential for evolutionary change
Constancy or fidelity – pollinators learn the flower characteristics and visit them preferentially
Precision pollen transfer
Attract appropriate pollinator using attractive colors, odors, shapes, sizes
Some flowers specialized for particular pollinators
Birds – odorless red flowers
Bees – blue, purple, yellow or white flowers with a sweet odor
If pollinator becomes extinct, plant may also face extinction (pollination syndrome)

23
Seed-dispersal coevolution
Influenced both plant and animal seed-dispersal agent
Plant may have juicy, sweet fruit with small seed to readily pass through gut
Plants may signal fruit ripeness with color change

Domestication – artificial selection for traits desirable to humans
Agriculture originated 10,000 – 5,000 years ago independently in at least 10 different locations
African bottle gourd, bread wheat, corn, rice
Shattering – wild fruit breaks apart and disperses seeds
Loss of this trait makes it easier for human harvest
24
Human Influences on Angiosperm Diversification

© 2016 Pearson Education, Inc.
PLANT GROUP
Mosses and other
nonvascular plants
Gametophyte
Reduced, dependent on gametophyte for nutrition
Ferns and other
Seedless vascular plants
Reduced, independent
(photosynthetic and free- living)
Dominant
Seed plants (gymnosperms and angiosperms)
Reduced (usually microscopic), dependent on
surrounding sporophyte tissue for nutrition
Sporophyte
Dominant
Gymnosperm
Microscopic female
gametophytes (n) inside
ovulate cone
Angiosperm
Microscopic female
gametophytes
(n) inside these parts
of flowers
Microscopic
male
gametophytes
(n) inside
these parts
of flowers
Sporophyte
(2n)
Sporophyte
(2n)
Gametophyte
(n)
Example
Gametophyte
(n)
Microscopic male
gametophytes (n)
inside pollen cone
Sporophyte
(2n)
Sporophyte
(2n)
Dominant

pollen

Figure 26.21 Gametophyte-sporophyte relationships in different plant groups

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Charophytes or charophycean is the group of green algae that is closest related
To the kingdom

Plantae

Overview of Plants

Origin

Green algae are named for their grass-green chloroplasts. These
are similar to plants’ chloroplasts in ultrastructure, pigment
composition and ability to store starch.

Within the groups of green algae, the members of the Phylum
Charophyta (charophyceans) are the closest relatives to land
plants. Land plants evolved from ancestors that were probably
similar to modern complex charophycean algae (see also figure
29.1- the term streptophytes include charophyceans and true
plants).

Similarities between complex charophyceans (e.g. Chara) and plants:
• Molecular Genetics: Comparisons of the sequences of both nuclear and chloroplast genes point to

charophyceans as the closest living relatives of land plants
• In addition, the following traits are only shared by charophyceans and land plants

ü Cell walls: rose-shaped complexes are used for cellulose synthesis; plasmodesmata (channel for
communications between cells) are present

ü Formation of a phragmoplast (forms during plant cytokinesis to allow the formation of the new cell
wall separating the two daughter cells)

ü Sexual reproduction and structure of flagellated sperm
ü Peroxisome enzymes (that minimize loss of carbohydrates due to photorespiration)

New traits in plants (different from Charophyceans)

1. The presence of embryo: Embryophytes is a synonym for plants. A structure protects and feed the
zygotes and embryos
ü Multicellular and diploid
ü Zygotes and embryos retained
ü Depends on organic and mineral materials supplied by mother plant – placental transfer tissue

2. Distinct reproductive features:
a. Alternation of generations (sporic life cycle). A multicellular

diploid sporophyte in addition to the multicellular haploid
gametophyte in charophyceans. (Sporic life was present in other
algae but not in charophyceans)

b. Dry air resistant reproductive cell (sporopollenin-walled
spores)

c. Specialized structures to generate, protect, and disperse
reproductive cells (gametangia and sporangia)

3. Tissues arise from apical meristems at growing tips.

Other important adaptations were appearing with the evolution of
plants in the land (but not present in all plants, see figure 29.1

LE 29-4
Viridiplantae

Streptophyta

Plantae

Red algae Chlorophytes Charophyceans Embryophytes

Ancestral alga

Overview Plants

Gametophytes: haploid (n) generation
Role – to produce haploid gametes
(by mitosis)
Gametangia protects developing gametes from
drying out and microbial attack. Two types of
gametangia:
Antheridia –gametangia producing sperm
Archegonia –gametangia enclosing an egg

Fertilization: Sperm and egg and fuse to form diploid
(2n) zygote. Zygotes and embryos are retained in the
gametophyte tissue, protected and fed (by placental

transfer tissue) and grow into multicellular diploid (2n) sporophytes.
Sporophytes develop protective structures named sporangia, where sporopollenin-walled spores
are produced. (Sporopollenin is a tough material that prevents cellular damage)

During evolution, plant sporophytes became larger and more complex
See table 29.1 in your book

Bryophytes: The monophyletic liverwort, moss, and hornwort phyla are together known informally as
the bryophytes. Bryophytes illustrate early-evolved features of land plants, such as a sporic life cycle
involving embryos that develop within protective, nourishing gametophyte tissues
Distinguishing bryophyte features:

ü Gametophytes are the dominant generation as opposed to dominant sporophyte generation in
other plants

ü Sporophytes are dependent on gametophyte – small and short lived. In other plants, sporophytes
are independent, large and long-lived

ü Nonvascular – lacking tissues for structural support and conduction found in other plants
(bryophytes are shorter that most of other plants)

See
the
life
cycle
of
the
moss
Sphagnum,

Figure
29.7
as
model
of
life
cycle
of

bryophytes

Overview Plants

Vascular Plants or Tracheophytes. The presence of vascular tissue gives name to the Vascular
Plants or Tracheophytes. Go to figure 29.1 and note that a new trait appears for vascular plants:
Lycophytes, pteridophytes, and other vascular plants generally possess stems, roots, and leaves having
vascular tissues composed of phloem and xylem, cuticle, and stomata
Vascular tissue: complex conducting tissue found in vascular plants. Compound by xylem and phloem

Xylem: Dead cells conducting water and minerals
Phloem: Living cells conducting nutrients derived from photosynthesis (sugar, sap: sugar-rich
water solution).

Lycophytes, pteridophytes are also known as seedless vascular plants, because they diverged form other
plants before the appearance of the seed, but as other vascular plants, have specialized organs:
Stems: Contain vascular tissue (phloem and xylem) and lignin and produce leaves and reproductive
structures
Roots: Specialized for uptake of water and minerals from the soil
Leaves: Photosynthetic function, and conservation of water:

ü Waxy cuticle present on most surfaces of vascular plant sporophytes –prevents dessication
ü Cutin found in cuticle – helps block pathogens
ü Stomata – pores that open and close to allow gas exchange while minimizing water loss

Leaves are more developed in most pteridophytes (euphylls or megaphylls, see figure 29.1 and 29.21)
Seedless vascular plants (lycophyte and pteridophyte) life cycle

ü Lycophyte and pteridophyte reproduction is limited by dry conditions, as is the case for bryophytes
(needs water for the flagellated sperm to swim )

ü However, if fertilization occurs, lycophytes and pteridophytes can produce many more spores due
to their larger sporophyte generation

o Vascular plant sporophytes are dependent upon maternal gametophytes for only a
short time during early embryo development

o Stems of vascular plant sporophytes are able to produce branches, forming relatively
large adult plants having many leaves

See the fern life cycle figure 29.12 and the video in Bb
The ferns are pteridophytes, note the specific structures in the fern: rhizome, fronds, sori
Compare seedless vascular plants vs. bryophytes. Make your own table.

Clades Primitive Features Advanced Features
Bryophytes -Nonvascular

-Only moist
environments
-Small
-Motile sperm
-Needs water to
reproduce

-Cuticle
-Stomata
-Rhizoid (…different than
rhizomes)
-Gametangia

Seedless Vasc. Plants -Motile sperm with
flagellum
-Needs water to
reproduce
-Only moist
environments
-Small
Gametophyte

-Cuticle
-Stomata
-Roots and Leaves
-Vascular system
-Structural support
-Dominant Sporophyte
-Independent
Gametophyte

Advantageous features for the adaptation to
the land.

Overview Plants

Seed plants or spermatophytes (meaning seed plants) are descendants from vascular plant ancestors
that developed the following critical innovations for life in land:
Reproductive innovations:

ü Seeds: allow plants to reproduce in diverse habitats
ü Pollen: allows seed plants to disperse male gametophytes
ü Ovules: provide protection and nutrition to female gametophytes and embryos
ü Wood: strengthens plants, allowing them to grow tall and produce many branches, leaves, and

seeds
To better understand the three first of these new innovations, let’s analyze what is new in the life cycle of
seed plants:

1) Seed plants produce heterospores. In
most seed plants, adult sporophytes develop
two different kinds of sporangia:
microsporangia & megasporangia (instead
of only one sporangia).
Microsporangia produce microspores by
meiosis and megasporangia produce
megaspores by meiosis.

2) Microspores undergo mitosis & develop
into pollen grains, which are the young
male gametopphytes

3) Macrospores undergo mitosis & produce
female gametophytes (mega-gametophytes)
containing eggs within archegonia. An ovule

consists of a megasporangium surrounded by one or two layers of tissue called integuments. The
megasporangium produces spores that develop into mega-gametophytes. These mega-gametophytes
remain within the tissues of the ovule and produce one or more egg cells

4) After fertilization, ovules develop into seeds. Mature seeds are ready for dispersal of the diploid
generation and contain:

embryonic sporophyte (2n)
stored food
protective coat

Use the following table to recognize the three
reproductive innovations: seeds, pollen and
ovules. Two other derived traits related to
reproduction are listed in the table (heterospory,
already discussed, and reduced gametophytes).
Remember that dominance of sporophyte
domination and reduction of gametophyte is a
trend in plant evolution (see figure )

Overview Plants

Read in your book: 1) which are the ecological advantages of the seeds? Page 593.
On your own: why do you think that pollen is a critical innovation in plants?

Seed plants include Gymnosperms (naked seeds) and Angiosperms (enclosed seeds, flowering plants).
Gymnosperms include several groups; we are going to pay more attention to Conifers. See the figure
30.7 for the life cycle of the genus Pinus ( a conifer)

Overview Plants

Compare the reproductive cycles of Gymnosperms and Angiosperms, what is common to them?
What is different? See video in bb
Reproductive cycle in Pinus, a Gymnosperm:

Reproductive cycle in angiosperms, (flowering plants):

Overview Plants

Critical innovations in Angiosperms; Flower, endosperm, fruits
A flower is a reproductive shoot, a stem branch that produces reproductive organs instead of leaves

Petals: attract animals for pollination.
Sepal: protective layer of flower buds.
Stamen: produce and disperse pollen.

anther: clusters of microsporangia (usually four) that produce pollen and then open to
release it
filament: sustain the stamen

Pistil: fused carpels (could be one, or more carpels fused)
Carpel: Vase –shaped structure that produce, enclose and nurture female gametophytes.
Contains veins of vascular tissue that deliver nutrients from the parent sporophyte to the
development gametophyte.

stigma: receives and recognizes pollen of the appropriate species or genotype. Only appropriate
pollen will be allowed to germinate
style: long middle portion; encloses the elongated pollen tube which delivers nonflagellate sperm
cells to ovules.
ovary*: Encloses and protects ovules, also develop into fruits.

Ovaries are also considered a critical innovation in angiosperms and is not present in
gymnosperms. Ovaries develops into fruits

Within the ovule:

Diploid cell produces 4 megaspores by meiosis (3 die) and one is left.
Surviving megaspore generate female gametophyte by mitosis
Female gametophyte consists of 7 cells, one of which is the egg cell

Within the anther:

Diploid cells undergo meiosis producing 4 tiny, haploid spores (microspores)
Pollen grains are immature male gametophytes. At the time of dispersal, the pollen grain is a
two- or three-celled male gametophyte produced by mitotic division

Overview Plants

During a later phase of development, a mature male gametophyte produces sperm cells

Double fertilization:
Pollen grains (immature male gametophytes) from the stamen are dispersed by the wind or transported by
pollinators to the stigma of a flower.
Pollen germinates and delivers two sperms to the female gametophytes by means of a long pollen tube,
that is enclosed, fed and guided by the style. Once the sperms reach an ovule in the ovary double
fertilization occurs. Double fertilization involves two events:

ü True fertilization: one sperm nucleus fuses with the egg to produce a diploid zygote that develops
later into a young sporophyte

ü Triple fusion: the other sperm nucleus fuses with the two nucleus of the central cell, generating
the first cell of the nutritive endosperm tissue

Double fertilization and therefore endosperm are present in angiosperms, but not in gymnosperms.
Both are derived traits of angiosperms and the presence of endosperm is considered a critical innovation
in angiosperms because provide a more efficient food storage to the seed.

Fertilized ovules develop into seeds, containing the young embryo (2n), the endosperm (result from
triple fusion) and the coat (produced by sporophyte integuments).
Ovaries and other parts develop into fruits. Ovary wall changes into a fruit wall (pericarp), and the
ovules into seeds
Fruit is a structure that encloses and helps disperse seeds. Dispersal helps reduce competition and
allows colonization of new sites. Variation in mature fruits reflects seed dispersal adaptations.
Mature seeds to be dispersed contain embryos that become dried and are protected by desiccation-
resistant proteins and a tough seed coat. These adaptations enable seeds to withstand long periods of
dormancy (metabolic slow down)

Seed germination and seedlings
Germination occurs only if seed encounters favorable conditions. Embryo absorbs water, becomes
metabolically active, and grows out of seed coat (seedling)

Tube cell

Tube cell nucleus

Generative
(sperm-producing)
cell

Pollen coat
and wall

Dominant
independent
sporophyte

Dependent
gametophytes

(b) Sporophyte-dominant flowering plant (oak)

Flowers

(top left): © Biodisc/Visuals Unlimited

Ovule

242 µm

Antipodal
cells

Two nuclei
of central cell

Synergids

Sporangium

Megaspore
wall

Female
gametophyte
(within
megaspore
wall)

Attachment
to ovary

242 µm

Egg cell

Integuments

Micropyle
opening

Overview Plants

The Role of Coevolution in Angiosperm Diversification
Coevolution: the process by which two or more species of organisms influence each other’s evolutionary
pathway. Most read: The Role of Coevolution in Angiosperm Diversification

Co-evolutionary interactions between flowering plants and animals that serve as pollen- and seed-
dispersal agents played a powerful role in the diversification of both angiosperms and animals

• Pollination Coevolution Influences the Diversification of Flowers and Animals.
Pollinators transfer pollen from the anthers of one flower to the stigmas of other flowers of the
same species. Pollinators foster genetic variability and plant potential for evolutionary change

o Constancy or fidelity – pollinators learn the flower characteristics and visit them
preferentially

o Precise pollen transfer
o Attract appropriate pollinator using attractive colors, odors, shapes, sizes
Which advantages does animal pollination have over wind pollination?
What is the pollination syndrome?

• Some flowers specialized for particular pollinators
• Birds – odorless red flowers
• Bees – blue, purple, yellow or white flowers with a sweet odor
• If pollinator becomes extinct, plant may also face extinction

• Seed-Dispersal Coevolution Influences the Characteristics of Fruits and Animals As in the
case of pollination, coevolution between plants and their animal seed-dispersal agents has
influenced both plant fruit characteristics and those of seed-dispersing animals.

o Plant may have juicy, sweet fruit with small seed to readily pass through gut
o Plants may signal fruit ripeness with color change

Overview Plants

Plant Transport

Vascular tissue: complex conducting tissue found in vascular plants. Compound by xylem and phloem

Xylem: Dead cells conducting water and minerals
Phloem: Living cells conducting nutrients derived from photosynthesis (sugar, sap: sugar-rich
water solution).

See the video and name the parts of the part of the plants and describe the process

Vascular tissue is present in the three plants’ organs: root, stem and leaves (in vascular plants).

Wood is listed as a critical innovation that
appears in many seed plants. How is it possible
the horizontal growth of the stem that produces
the strong trunks that sustain the trees?

While herbaceous plants produce mostly primary
vascular tissues, woody plants produce primary
and secondary vascular tissue. Woody plants
begin life as herbaceous seedlings that possess only
primary vascular systems. Secondary vascular
tissue is formed from secondary or lateral meristems.
Secondary xylem – wood
Secondary phloem – inner bark (bark has both
outer bark of mostly dead cork cells and inner bark
(secondary phloem)

Overview Plants

Secondary vascular tissues are produced by two types of secondary meristems (lateral
meristems)

ü Vascular cambium
ü Cork cambium

Vascular cambium

ü Produces secondary xylem to its interior and
secondary phloem to its exterior

ü Secondary xylem conducts most of a woody
plant’s water and minerals

ü Secondary xylem may transport water for several
years

ü Usually only the current year’s production of
secondary phloem is active in food transport

Cork cambium
ü Produces cork
ü Cork cells dead when mature and layered with

lignin and suberin

PlantsA
Plants Fall 2016

Kingdom Plantae

Viridiplantae
Streptophyta
Plantae

Red algae
Chlorophytes
Charophyceans
Embryophytes
Ancestral alga

Charophyceans or charophytes: closest land plant ancestors
They are green algae, but are closer related to plants than other green algae as chlorophytes

Chara

Macro
Micro
Chara: A genus of complex charophyte resembling land plants

Oogonium (archegonium) with one single egg
Antheridium with sperm
Chara, sexual organs
Sex organs in Chara
Oogonium (pl: oogonia) Female flask-shaped structure containing each one egg (non motile). Covered with cell layer: multicellular sex organ.
Antheridium (pl: antheridia) Male round structure, also multicellular. Produce motile flagellated sperms

Spirogyra: Another genus of complex charophyte resembling land plants

The first plants probably originated from extinct relatives of Chara or other charophyceans
They already had similarity to plants as:

Same food reserve: starch
Same photosynthetic pigments:
chlorophylls a and b
carotenes
xanthophylls
Similar structure of flagella
Similar cell division structure
Molecular markers: rRNA indicates homology

Once the primitive plants arrived on land they adapted to new conditions of gravity, humidity, substrate, temperature.
The ones who survived transformed in land plants.

New in true plants:

Alternation of generations
Multicellular, dependent Embryo
Walled spores produced in sporangia
Apical meristems

New in true plants:
Alternation of generations
Plants alternate between two multicellular stages:
the haploid gametophyte that produces haploid gametes by mitosis
the diploid sporophyte that produces haploid spores by meiosis
In land plants this alternation of generations is heteromorphic (both stages are morphologically different); in some green algae it is isomorphic. Charophyceans do not have alternation of generations.

Alternation of generations
Plants Sexual Life Cycle

Sexual cycles in different organisms

General plant cycle
The sporophyte is the multicellular diploid generation (2n).
The sporophyte contains the sporangium (pl. sporangia), the structure specialized in producing spores (n) by meiosis.
The gametophyte is the multicellular haploid generation (n).
The gametophyte contains the gametangium, the structure specialized in producing gametes.
The archegonium (pl. archegonia) is the female gametangia, produce eggs (the female gametes).
The antheridium (pl. antheridia) is the male gametangia, produces sperm (the male gametes)

New in true plants (Embryophytes):
Multicellular, dependent Embryo

Viridiplantae
Streptophyta
Plantae

Red algae
Chlorophytes
Charophyceans
Embryophytes
Ancestral alga

Meristems are sites of repeated cell division of unspecialized cells. These cells differentiate, and become specialized in relation to the function they will perform.

During the colonization of land, new adaptations appear in plants

Bryophytes are dominated by the gametophyte stage

Bryophytes are anchored to the substrate by rhizoids. Rhizoids are not true roots.

The flagellated sperm produced by bryophytes must swim through a film of water to reach and fertilize the egg

In bryophytes, the gametophytes are larger and longer-living than sporophytes. We say that gametophyte (n) is the dominant generation

The height of gametophytes is constrained by lack of vascular tissues

Bryophytes are represented today by three phyla of small herbaceous (non-woody) plants:
Liverworts, phylum Hepatophyta. Example: Marchantia
Mosses, phylum Bryophyta. Example: Polytrichum
Hornworts, phylum Anthocerophyta. Example: Anthoceros sp.

Liverworts, (Hepatophyta)

Worts=Herbs
Liverworts = liver-like herbs
Marchantia
The body is called thallus (pl thalli). The thallus is the gametophyte portion of the life cycle.
Asexual reproduction: gemmae in the gemma cups
Sexual reproduction:
On male plants: Anteridiophores containing antheridia
On female plants: archegoniophores containing archegonia
See pictures in your book and preserved specimens
Rhizoids (no real roots)

Liverwort, microscopic slide showing:
Cuticle
Pore (but no yet stoma)
Rhizoid (not a real root)

1 m

Thallus
(Gametophyte)
n=haploid
Gametangiophore
(archegoniophore) of a
female plant

Marchantia polymorpha, a “thalloid” liverwort

Gemma cup
(asexual reproduction from the tallus, dispersed by rain)

Rhizoids
(to anchor to the substrate)

22
Figure 29.9 Exploring: Bryophyte Diversity

Marchantia, sexual reproduction
Marchantia,
asexual reproduction by gemmae
Female plant
Male plant

Gemmae are splashed out of the cups by raindrops and can they grow in new gametophytes. Each identical to the parent plant that produced it by mitosis

1 m

Polytrichum commune,
hairy-cap moss
Capsule
Seta
Sporophyte

Gametophyte

Mosses (Bryophyta)

24
Figure 29.9 Exploring: Bryophyte Diversity

Gametophyte
Gametophore
Rhizoids
PAGE 269
Ex. 15.4
Answer questions

LE 29-8
Male
gametophyte
“Bud”
Spores develop into
threadlike protonemata.
Protonemata
“Bud”

The haploid protonemata produce “buds” that grow into gametophytes.
Raindrop
Sperm
Antheridia
Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively.

Egg
Haploid (n)
Diploid (2n)
Key
A sperm swims through a film of moisture to an archegonium and fertilizes the egg.

Archegonia
Rhizoid
Female
gametophyte

FERTILIZATION
(within archegonium)
Archegonium
Zygote
Embryo

Calyptra

Young
sporophyte

Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte.
The diploid zygote develops into a sporophyte embryo within the archegonium.

Capsule
(sporangium)
Seta
Foot

Mature
sporophytes
Capsule with
peristome (SEM)
Female
gametophytes
Moss Life Cycle

These figures are taken from the moss cycle
(preview slide)

To distinguish antheridium from archegonium, look for sterile jacket and spermatogenic tissue in antheridium.

Moss mature capsule

Seedless Vascular Plants (Tracheophytes)
The First Plants to Grow Tall
Bryophytes were the prevalent vegetation during the first 100 million years of plant evolution
The earliest vascular plants date to 425 million years ago
Vascular tissue allowed these plants to grow tall
Early vascular plants lacked seeds (seedless).

Vascular Tissue
Vascular tissue: special tissues in plant that conduct water and minerals

Xylem: conducts water and minerals
Xylem conveys water and dissolved minerals upward from roots into the shoots. Dead cells make tracheids strengthened by lignin, which provide structural support
Phloem: conducts the products of photosynthesis
Phloem consists on living cells and transports organic nutrients from where they are made to where they are needed.

Seedless Vascular Plants
Have vascular tissue, specialized in water and food transport
Sporophyte (2n) is the dominant generation
Most of them have true roots, stem and leaves with stomata

Distinguish two clades:
Lycophytes: Club mosses
Pterophytes, most are Moniliophytes: Whisk ferns, horstails and ferns

Seedless vascular plants can be divided into two clades
Lycophytes
(club mosses and their relatives)

Monilophytes
(ferns and their relatives)

Figure 26.20 Lycophytes and monilophytes (seedless vascular plants)

Phylum Lycophyta:

Giant lycophytes thrived for millions of years in moist swamps
Surviving (extant) species are small herbaceous plants

Selaginella (Spike Moss) resurrection plant
Lycopodium: club mosses
Strobili (pl), strobilus (sin): region of the stem specialized in spore formation in Lycopodium (fig 15-19) Note small leaves
strobilus

Sporophylls and Spore Variations
Sporophylls are modified leaves with sporangia
Strobili are cone-like structures formed from groups of sporophylls

https://en.wikipedia.org/wiki/File:Rose_of_Jericho.gif

Resurrection plant

Clade Pterophytes (Monilophytes)
Ferns, Horsetails and Whisk Ferns
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
Horsetails were diverse during the Carboniferous period, but are now restricted to the genus Equisetum
Whisk ferns resemble ancestral vascular plants but are closely related to modern ferns

Psilotum (whisk ferns)
Small
Photosynthetic stems
Aerial spores
No roots, symbiosis with fungi
No true leaves
Rhizoids
whisk ferns

Equisetum (horsetails)
Clusters of leaves in nodes
Stem contains Silica
Nodes and internodes
Photosynthesis only in the stem
horsetails

Horsetail gametophytes are small and green (photosynthetic)

ferns

FERNS

Dissected leaves called fronds
Underground horizontal stem (rhizome)
Real roots
Sori (clusters of sporangia) in the undersurface of fronds
Unrolling young fronds (fiddleheads)
Abundant, with ornamental value

ferns anatomy
15-26, 15-27 ,PAGE 281

Unrolling young fronds (fiddleheads)

Underground horizontal stem (rhizome)
Real roots

Sori (clusters of sporangia) in the undersurface of fronds

15-28 ,PAGE 282

Vascular tissue

1 m

The life cycle of a fern

Slide 29

Slides 27,28
Living
Specimen
Check sori