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Plant Evolution &
Diversity – Ch. 22-25
Kingdom Protista: Algae & Protozoa
• Simple Eukaryotes – mostly single-celled
• Organisms in this Kingdom don’t fit clearly into
what we call plant, animal, or fungi.
• Most diverse eukaryotic Kingdom (>60,000
species).
• We are interested in this Kingdom because of the
Chlorophytes & Charophyceans - green algae.
The line between Kingdom Protista and Kingdom
Plantae is still being discussed……
Characteristics of Green Algae - Chlorophytes
• .
• Can live symbiotically with fungi as lichens
Fig 28.30
Volvox - freshwater
Ulva – sea lettuce
Caulerpa - intertidal
Characteristics of Green Algae - Charophyceans
• 500 million years ago, the algal ancestors of plants
formed a green carpet on the edge of lakes and
coastal salt marshes
Coleochaete, a simple charophyte.
Chara, an
elaborate
charophyte.
Plants
• Plants are..
• So how are they different from
Charophyceans??
What challenges did plants face when
they “moved” onto land?
Adaptation to life on Land – All plants have:
1. Apical Meristems
2. Alternation of generations life cycle
1. Apical Meristems –
2. Alternation of Generations
•
2 multicellular life stages:
1. Sporophyte:
• Spores – haploid cells that can grow into a
new, multicellular, haploid organism (the
gametophyte) without fusing to another cell.
2. Gametophyte:
•
Egg & sperm fuse to form the diploid zygote,
which divides by mitosis to form the sporophyte
Spores produced in sporangia
• Sporangia =
• sporangia divide by meiosis to form the haploid
spores
sporocytes
•
•
Gametangia =
2 types of gametangia:
1. Archegonia – produce eggs
2. Antheridia – produce sperm
• Sperm travel to the egg, fertilizing it within the
archegonia.
Other examples of adaptations to life on land:
(not all plants have the following):
1. Cuticle –
2. Secondary compounds –
3. Roots - absorb water and minerals from the soil
4. Shoots - stems and leaves to make food.
5. Stomata – openings in the leaf surface to allow
gas exchange for photosynthesis and to regulate
water loss.
More Adaptations
4. .
5. A vascular system that transports food & water
from roots to shoots and vice versa.
Key
Vascular
tissue
Spores
Leaf
Spores
Flagellated
sperm
Alga
Water supports
alga. Whole alga
performs photosynthesis;
absorbs water,
CO2, and
minerals from
water.
Flagellated
sperm
Leaf
Stem
Stem
Roots
Roots
Flagellated
sperm
Holdfast
(anchors alga)
Moss
Stomata only on sporophytes;
primitive roots anchor plants,
no lignin; no vascular tissue;
fertilization requires moisture
Fern
Stomata; roots anchor plants,
absorb water; lignified cell
walls; vascular tissue;
fertilization requires moisture
Key
Vascular
tissue
Pollen
Seed
Leaf
Stem
Roots
Pine tree
Stomata;
roots anchor plants, absorb water;
lignified cell walls; vascular tissue;
fertilization does not require moisture
Earliest group: Nonvascular Land Plants
•
•
Earliest land plants
3 Groups:
1. liverworts
2. hornworts
3. mosses
• .
•
•
Peat moss (sphagnum): doesn’t decay rapidly,
stores 400 bil tons of carbon
Gametophyte is the dominant generation:
liverworts
hornworts
Mosses
Moss life cycle
• Gametophytes make up a bed of moss
• The zygote develops within the gametangium
into a mature sporophyte, which remains
attached to the gametophyte
– Meiosis occurs in sporangia at the tips of the
sporophyte stalk
– Haploid spores are released from the sporangium
and develop into gametophytes
Copyright © 2009 Pearson Education, Inc.
Key
Haploid (n)
Diploid (2n)
Gametophytes (n)
5 Mitosis and
1
Male
Sperm (n)
development
Female
gametangium
Spores (n)
Female
1
Egg (n)
Fertilization
Sporangium
Stalk
2
Meiosis
4
Zygote (2n)
Sporophyte (2n)
3 Mitosis
and development
Step 1: Moss gametophyte (n)
Step 2: Within the gametophyte, archegonia make eggs
and antheridia make sperm, by mitosis:
Archegonia
Sac full of sperm
egg
Step 3: Sperm swims to the egg fertilization (create of a 2n zygote)
Step 4: mature
sporophyte capsules
release spores….which
grow into new
gametophytes
Peat bogs –
Vascular Plants
• Vascular tissue:
– Xylem =
– Phloem =
• Dominant generation = sporophyte
Fern life cycle
• Fern gametophytes are small and inconspicuous
– The zygote initially develops within the female
gametangia but eventually develops into an
independent sporophyte
• Sporangia develop on the underside of the leaves
of the sporophyte
– Within the sporangia, cells undergo meiosis to
produce haploid spores
– Spores are released and develop into gametophytes
Copyright © 2009 Pearson Education, Inc.
Two major groups of seedless vascular plants:
1. Lycophytes
- .
- were tree-like in the Carboniferous period
- 3 kinds: club mosses, spike mosses, and quillworts
Club moss
Spike moss
Quillwort
2. Pterophytes – 3 kinds
a) Whisk ferns –
b) Horsetails –
c) Ferns – produce clusters (sori) of sporangia on
underside of leaves (fronds)
Whisk fern
Horsetails
Ferns
1
Key
Haploid (n)
Diploid (2n)
Sperm (n)
5 Mitosis and
Female
gametangium (n)
development
Gametophyte (n)
Spores (n)
Egg (n)
Fertilization
Meiosis
4
Clusters of
sporangia
2
Zygote (2n)
New sporophyte (2n)
3 Mitosis and
development
Mature sporophyte
Forests of the Carboniferous period (290-360
mil years ago):
• Swampy forests – slow decay in low O2, formed
deep layers of organic matter
• Heat + pressure + time ----> coal
• Pulled lots of CO2 out of atmosphere, cooling the
earth & forming glaciers
• Larger species died out when climate became drier
Terrestrial Adaptations of Seed Plants
1. Seeds replace spores as main means of dispersal.
• Why?
2. Gametophytes became reduced and retained
within the sporophyte
3. Pollen & Pollination - freed plants from the
requirement of water for fertilization.
1. Seeds replace spores as main means of dispersal.
• old way (ferns & mosses) = spores released from
sporangia to disperse and develop into
gametophytes
• new way:
• ovule = female sporangium + female spore.
Female gametophyte develops within the spore &
produces eggs.
• after fertilization, the ovule becomes the seed
• seed = sporophyte embryo + food supply (mature
ovule tissues)
2. Reduction of the gametophyte:
3. Pollen & Pollination
• Pollen =
• Pollination =
• Pollen tube brings sperm to egg within the ovule
Two types of seed plants:
1. Gymnosperms
•
2. Angiosperms
•flowering plants
•Most diverse
•Evolved from gymnosperms:
Gymnosperms
•
Four major groups
1. Ginko biloba
2. Cycads (look like palms)
3. Gnetophytes
4. Conifers – cone-bearing trees
 .
 Needle-shaped leaves to reduce water loss
during drought
Cycads
Ginko biloba
Gnetophytes
Ephedra
Welwitschia
Conifers
oldest
Tallest
Pine life cycle
• A pine cone holds all of the tree’s reproductive
stages: spores, eggs, sperm, zygotes, and embryos
• The male gametophyte is a pollen grain, released
from pollen cones and carried by wind to female
cones
• Female ovulate cones carry two ovules on each
stiff scale - Each ovule contains a sporangium
Copyright © 2009 Pearson Education, Inc.
1 Sporangia produce
Scale
spores; spores develop
into pollen grains.
Sporangium (2n)
4 A haploid spore cell
Ovule
develops into female
gametophyte, which
makes eggs.
5 Pollen grows
tube to egg
and makes
and releases
sperm.
Meiosis
Meiosis
Pollen grains
(male gametophytes) (n)
Spore mother cell (2n)
Integument
3 Pollination
Egg (n)
Fertilization
Sperm (n)
Male gametophyte
(pollen grain)
2 Ovulate cone
bears ovules.
Female
gametophyte (n)
Zygote
(2n)
Mature sporophyte
Seed coat
Seed
Embryo (2n)
Food supply
Key
Haploid (n)
Diploid (2n)
6 Zygote develops
7 Seed germinates,
and embryo grows into seedling.
into embryo, and
ovule becomes seed.
• In pollination, a pollen grain lands on a scale in
an ovulate cone and enters an ovule
• Fertilization occurs a year after pollination,
when a sperm moves down a pollen tube to the
egg to form a zygote
– The zygote develops into a sporophyte embryo,
and the ovule becomes a seed, with stored food and
a protective seed coat
• The seed is a key adaptation for life on land and a
major factor in the success of seed plants
Copyright © 2009 Pearson Education, Inc.
Angiosperms
•
Difference from gymnosperms?
•
Seeds are enclosed in the moist reproductive
tissue called the ovary….which becomes the fruit
•
More insects and animals for pollination, less dependent
on wind.
2 major groups
•
1. Monocots
2. Dicots
The flower is the centerpiece of angiosperm
reproduction
• Flowers contain separate male and female
sporangia and gametophytes
• Flowers usually consist of sepals, petals, stamens
(which produce pollen), and carpels (which
produce eggs)
• Stamens include a filament and anther, a sac at
the top of each filament that contains male
sporangia and releases pollen
Copyright © 2009 Pearson Education, Inc.
Evolutionary success of Angiosperms
due to:
1. Increased water transport efficiency due to
improvement in xylem tissue:
2. Flowers – attract pollinators
3. Fruits – many forms for variety of dispersal
mechanisms
1 Haploid spores in anthers develop into
pollen grains: male gametophytes.
Pollen grains (n)
3 Pollination and
growth of
pollen tube
Meiosis
Stigma
2 Haploid spore in each ovule
develops into female gametophyte, which produces an egg.
Stigma
Anther
Pollen grain
Pollen tube
Meiosis
Egg (n)
Ovule
Ovary
Sporophyte (2n)
Ovule
Sperm
7 Seed germinates,
and embryo
grows into
plant.
Seeds
6 Fruit
Food supply
(mature
ovary)
Seed
coat
Fertilization
Key
Haploid (n)
Diploid (2n)
5 Seed
4 Zygote
Embryo (2n)
(2n)
The structure of a fruit reflects its function in seed
dispersal
• Fruits, ripened ovaries of flowers, are
adaptations that disperse seeds
– .
– .
– Fleshy, edible fruits attract animals
Copyright © 2009 Pearson Education, Inc.
Angiosperms sustain us—and add spice to our diets
• Most human food is provided by the fruits and
seeds of angiosperms
– Spices such as nutmeg, cinnamon, cumin, cloves,
ginger, and licorice are also angiosperm fruits
Copyright © 2009 Pearson Education, Inc.
Pollination by animals has influenced angiosperm
evolution
• 90% of angiosperms use animals to transfer
pollen
– Bats are attracted by large, highly scented flowers
– Wind-pollinated flowers produce large amounts of
pollen
Copyright © 2009 Pearson Education, Inc.
Plant diversity is an irreplaceable resource
• More than 50,000 square miles of forest are
cleared every year
– Replanted areas have greatly reduced biological
diversity
• Loss of forests has greatly reduced diversity of
life on Earth
– The loss of plant diversity removes potentially
beneficial medicines
– More than 25% of prescription drugs are extracted
from plants
Copyright © 2009 Pearson Education, Inc.
Ch. 9: flowers, fruits:
Angiosperm Reproduction
Fig 30.3
Notice the triploid stage!
•Double fertilization – one sperm unites with the egg to
form the 2n zygote, other sperm unites with the two
nuclei of the female gametophyte to form a 3n
endosperm – becomes food for the developing embryo
•Ovule matures into the seed – contains sporophyte
embryo & endosperm (food).
•Ovary (female sporangium tissues) matures into the
fruit.
The Angiosperm Life Cycle
• Male gametophyte =
• Female gametophyte = embryo sac, develops in
the ovule of the ovary. Produces egg
Development of Male Gametophyte (Pollen)
•
•
Anther is composed of pollen sacs (sporangium).
Inside pollen sac: diploid cells undergo meiosis
to form 4 haploid microspores.
• Each microspore divides by mitosis to make 2
cells:
1. Generative cell –
2. Tube cell –
•
The 2 cells enclosed in thick wall => pollen grain
Development of the Female Gametophyte
(Embryo Sac)
• Ovule = female sporangium
• Only one megaspore survives and divides by
mitosis 3 times to make 8 haploid nuclei.
Embryo Sac
= female
gametophyte
Antipodal
cells
2 polar
nuclei
Egg
Synergid cells
Fig 38.4
Angiosperm Reproduction
1. Pollen grain lands on stigma (= pollination)
2. Generative cell divides by mitosis to form 2 sperm
cells
3. Tube cell forms pollen tube
4. Sperm travel down pollen tube and enter embryo
sac
5. Double fertilization –
• Egg + sperm  zygote
• 2 polar nuclei + sperm  3n nucleus that
becomes the endosperm
Double fertilization
Maturation
• Embryo divides to form cotyledons (= seed
leaves) and meristems
• Ovule is now a seed – dehydrates & becomes
dormant (low metabolism, no growth).
• Ovary tissues divide & mature into fruit