Transcript Plant evolution

Imagine sitting in the sunshine on a sandy riverbank on
the Serengeti 500 million years ago. As waves gently lap
against the bank, a warm gentle breeze rolls off the plain.
Although all seems well at first, an eerie feeling soon comes
over you. As you look around, something seems terribly
wrong. There are no birds flying in the sky. There are no
flies nipping at your toes. In fact, there are no animals
anywhere in sight. Worse yet, there aren't even any plants!
Everywhere you look, the plain appears devoid of living
things. Where did they all go? The answer is that they
went nowhere. This is because 500 million years ago
virtually all visible organisms still lived in water. Yet all of
this was about to change. Aquatic organisms were poised
to invade the land.
What aquatic organisms were about to make the
transition?
What obstacles would the first land plants
have had to overcome to make this transition
to land?
(Identify at least 3)
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Share your ideas with your neighbor
Introduction
More than 280,000 species of plants inhabit Earth
today.
 Most plants live in terrestrial environments,
including deserts, grasslands, and forests.
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Some species, such as sea grasses, have returned to
aquatic habitats.
Land plants (including the sea grasses) are thought
to have evolved from a certain green algae, called
charophyceans.
Think about how each of the following
events profoundly shaped and affected
the course of organic history and why
each step was necessary for the
following events to occur. (think
structure and function).
The Eight Monumental
Events in the History
of Plants
1. The evolution of the first form of life.
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3.5 billion years- oldest prokaryotic fossil
2. The origin and development of
photosynthetic cells.
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2.7 billion years BP, accumulation of oxygen
increases in atmosphere.
3. The appearance of cells with
organelles. What type of cell is this?
4. The acquisition of multicellular
construction.
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Oldest multicellular organism (algae) fossil is 1.2
billion years old
5. The ecological assault of plants on
land.
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Fossil record shows this to have occurred about
500 million years ago.
6. The evolution of conducting tissues.
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Approximately 420 million years ago
7. The evolution of seed plants.
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Oldest seed plants according to the fossil record are
about 360 million years old
8. The rise of flowering plants.
125 million years ago
Archaefructus sinensis
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What is
this called?
 1.
The first organisms to successfully
colonize dry land some 1.5 billion years
ago were probably part fungal and part
green algal creatures called lichens. The
fungal part afforded protection from
drying while the green algal part
conducted photosynthesis to supply food.
 2.
The first plants to invade land some
500 million years ago were probably
some form of photosynthetic freshwater
green alga, which during times of
periodic drought evolved novel land
adaptations (e.g., thick waxy coverings
with small holes, vascular tissues). These
first vascular plants were soon followed
by a fungal invasion, which radiated into
four major groups (imperfect fungi, land
molds, sac fungi, and club fungi).
3.About 450 to 425 million years ago, the
vascular land plants first radiated into a
group of spore-producing land plants
(whisk ferns, club mosses, horsetails,
ferns) and later, about 380 million years
ago, to seed-producing ferns that probably
gave rise to the gymnosperms and
angiosperms before going extinct.
 4.
Some 400 million years ago,
freshwater green algae gave rise to
another land group called bryophytes
(liverworts, hornworts, and mosses).
Because bryophytes did not acquire
vascular tissue, they remained short, tied
to moist environments, and relatively
inconspicuous.
5. Present-day gymnosperms, which
produce seeds encased in a seed coat and
little else, include four groups: cycads,
ginkos, gnetophytes, and conifers.
Gymnosperm reproduction represents
several evolutionary advances over that of
ferns, such as protected internal
fertilization, protected sperm passage, and
protected embryo development.
6. Angiosperms (vascular plants with
flowers and encased seeds) first appeared
about 180 million years ago and became
dominant about 65 million years ago.
Their domination was due primarily to
adaptations such as well-developed
vascular tissues, waxy surface secretions,
flowers that attract pollinating agents, and
seeds encased in tasty fruits that attract
animals that aid in seed dispersal.
7.The evolutionary trend seen in plant life
cycles toward dominance of the diploid
over the haploid phase can be understood
as a consequence of natural selection
favoring the hardier diploid phase thanks
to its ability to mask the expression of
harmful genes.
The timing of meiosis and fertilization does vary
among species.
 The life cycle of humans and other animals is typical
of one major type.
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Gametes, produced by meiosis,
are the only haploid cells.
Gametes undergo no divisions
themselves, but fuse to form a
diploid zygote that divides by
mitosis to produce a
multicellular organism.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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Plants and some algae have a third type of life cycle,
alternation of generation.
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This life cycle includes both haploid (gametophyte) and
diploid (sporophyte) multicellular stages.
Meiosis by the sporophyte produces haploid spores that
develop by mitosis
into the gametophyte.
Gametes produced
via mitosis by the
gametophyte fuse
to form the zygote
which produces the
sporophyte by mitosis.
Introduction
Life on Earth is solar powered.
 The chloroplasts of plants use a process called
photosynthesis to capture light energy from the
sun and convert it to chemical energy stored in
sugars and other organic molecules.
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1. Plants and other autotrophs are
the producers of the biosphere

Photosynthesis nourishes almost all of the living
world directly or indirectly.
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All organisms require organic compounds for energy
and for carbon skeletons.
Autotrophs produce their organic molecules
from CO2 and other inorganic raw materials
obtained from the environment.
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Autotrophs are the ultimate source of organic
compounds for all nonautotrophic organisms.
Autotrophs are the producers of the biosphere.
2. Chloroplasts are the sites of
photosynthesis in plants
Any green part of a plant has chloroplasts.
 However, the leaves are the major site of
photosynthesis for most plants.
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There are about half a million chloroplasts per square
millimeter of leaf surface.
The color of a leaf comes from chlorophyll, the
green pigment in the chloroplasts.
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Chlorophyll plays an important role in the absorption
of light energy during photosynthesis.
Chloroplasts are found mainly in mesophyll cells
forming the tissues in the interior of the leaf.
 O2 and water exit and CO2 enters the leaf through
microscopic pores, stomata, in the leaf.
 Veins deliver water
from the roots and
carry off sugar from
mesophyll cells to
other plant areas.
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Fig. 10.2
A typical mesophyll cell has 30-40 chloroplasts,
each about 2-4 microns by 4-7 microns long.
 Each chloroplast has two membranes around a
central aqueous space, the stroma.
 In the stroma are
membranous sacs,
the thylakoids.
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These have an internal
aqueous space, the
thylakoid lumen or
thylakoid space.
Thylakoids may be stacked
into columns called grana.
Fig. 10.2
Photosynthesis
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The requirements and the products for
cellular respiration are exactly opposite as
they are for photosynthesis.
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Animals use O2 and Green Plants use CO2.
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Each depends on the other for the gases that
they need to survive.
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Photosynthesis
6H2O + 6CO2 + Light
C6H12O6 + 6O2
Photosynthesis
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CO2 is diffused through the stomata.
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Water is taken up through the roots and
transported in the xylem vessels.
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Light energy is absorbed by the chlorophyll.
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O2 & H2O leave the plant through the stomata.
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Glucose and Starch are stored or used for
growth within the plant and travel in the
phloem.