Transcript Overview of Plantsx

Overview of Plants
The Evolution of Plants
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All plants are multicellular autotrophs
that make food by photosynthesis. All
plants contain chlorophyll.
Most plants are terrestrial. They and
fungi both descended from
multicellular protists.
Aquatic life was protected from cosmic
radiation by the water they lived in.
This was not true of the organisms that
began to move out onto the land.
Plants and fungi first colonized the
land about the same time, about 440
m.y.a. when atmospheric O2 and O3
(ozone) accumulated in large enough
amounts to protect the living organisms
from cosmic radiation.
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Before plants could survive on land, they
had to solve three serious problems:
They had to be able to absorb needed
minerals from the rocky surface of the
land.
They had to prevent water loss in the dry
environment and support their bodies.
They had to have a way to reproduce on
land.
Problems Solved!
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Absorbing Minerals: The first land plants did
not have roots. Symbiotic relationships called
mycorrhizae developed between the first land
plants and early fungi. The plants make
carbohydrates needed by both organisms by
photosynthesis, and the fungi absorb from the
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rocky land the minerals needed by both
organisms.
Conserving Water and Supporting the Plant
Body: The first land plants lived by the edges
of bodies of water so they could replace lost
water. As plants developed a watertight waxy
cuticle, they could then move into drier
environments. The plant cuticle is waterproof,
but it also is airtight. Plants developed
specialized holes in the cuticle called stomata
for gas exchange. Guard cells open and close
the stomata to exchange gases while
preventing water loss.
Plants do not have skeletons like animals
do. Instead, individual plant cells have stiff
cell walls made of cellulose for support.
They also use water pressure in the cell’s
central vacuole to help plant cells retain
their shape. Large plants have developed
special woody layers that also contribute to
supporting the plant body in air.
Reproducing on land: The gametes of land
plants must be able to move from the male
to the female plant without drying out.
Primitive plants still need water to
reproduce, but higher plants surround
sperm in multi-layered structures called
pollen grains, which are transmitted by
wind or animals, rather than water.
Evolution of a Vascular System
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The first land plants did not look
different above or below the ground.
As later land plants evolved, they
developed specialized structures
such as stems, roots, and leaves to
help them adapt to their new
environment.
A vascular system transports
materials like water and food
throughout the plant body. Early
plants also lacked a vascular
system. All materials had to be
transported by osmosis or diffusion.
This limited plant size. All nonvascular plants are very small.
Mosses have very simple vascular
tissue, but it is not well-developed.
They do not have a vascular system.
The first vascular plants appeared
430 m.y.a. Today, vascular plants
dominate almost every habitat.
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Modern vascular plants can
grow very tall, and have 3
features in common :
All vascular plants have a
dominant sporophyte
form in their life cycle.
All vascular plants have
specialized conducting
tissues called xylem
(transports water) and
phloem (transports food).
The bodies of vascular
plants have a central shaft
from which specialized
structures branch out. The
roots (below ground) are
different from the shoots
(above ground).
Alternation of Generations
 Plants exist in two life forms that alternate with each other: the sporophyte generation and
the gametophyte generation.
 The sporophyte generation is diploid and  The gametophyte generation is haploid and
undergoes meiosis to produce haploid
produces eggs or sperm by mitosis. The eggs
spores, which grow up into the
and sperm unite during fertilization to form
gametophyte.
the zygote, which grows into the diploid
sporophyte and completes the cycle.
(Meiosis
)
Haploi
d
Spores
Sporophyte
(diploid)
(Mitosis)
Fertilization !
(diploid zygote)
(Growth
by
Mitosis)
Gametophyte
(haploid)
eggs
sper
Evolution of Plant Life Cycles
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The life cycle of non-vascular plants is
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dominated by a large gametophyte generation
that supports a smaller, dependent sporophyte
generation.
The fern life cycle represents an intermediate 
stage in the evolution of plant life cycles.
In ferns and other seedless vascular plants, the
sporophyte is dominant and the gametophyte is
smaller, but independent and self-sufficient.
Non-vascular plants
(mosses and liverworts)
Large,
Dominant
Gametophyte
Small, Dependent
Sporophyte
In seed plants, the gametophyte has
become much smaller, and are entirely
dependent on the sporophyte generation
for all the necessities of life.
The seed plant you see is the sporophyte
generation. Gametophytes produce
either eggs or sperm, which are haploid.
Seedless vascular plants
(ferns)
Dominant
Sporophyte
Smaller, but
Independent
Gametophyte
Higher vascular plants
Large and
Dominant
Sporophyte
Small, Dependent
Gametophyte
Evolution of Seeds – Part 1: Ferns
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Following the development
of a vascular system, the
next great advance was the
development of seeds.
The first vascular plants
did not produce seeds.
Ferns reproduce using
spores.The great
carboniferous fern forests of
the Paleozoic Era needed a
moist climate. Like nonvascular plants, ferns have
swimming sperm and need
some water for fertilization
to occur.
 The fern gametophyte produces eggs in
organs called archegonia and sperm in organs
called antheridia. The same plant has both male
and female sex organs. When a film of water is
present, sperm are able to swim to the eggs and
fertilize them.
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The fern life cycle represents
an intermediate stage
between the lower plants and
the seed plants. The
sporophyte stage is
dominant, but the
gametophyte, while smaller,
is still able to live
independently.
The fern sporophyte
consists of roots,
underground stems called
rhizomes, and long, highly
divided leaves called fronds.
The fern gametophyte is a
small thin, heart-shaped
photosynthetic plant that
lives in moist places and is
no more than 1 cm in
diameter.
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Evolution of Seeds – Part 2:
sporophyte generation produces two
Gymnosperms  The
kinds of spores: microspores, which
The word gymnosperm means “naked
produce the male gametophyte, and
seed.” Gymnosperm seeds do not develop
megaspores, which produce the female
inside of a fruit (a mature ovary).
gametophyte.
Gymnosperms first appeared about 380
m.y.a., and were the first seed plants. The  Pollen grains are actually microspores, that
produce the male gametophyte and its
flowering plants (angiosperms) evolved
sperm.
from gymnosperms between 150-200 m.y.a.
 An ovule contains a megaspore that
and are the most recently evolved plant
produces the female gametophyte and its
phylum.
egg.
In seed plants, the gametophyte is very
 In many gymnosperms, the fertilized egg
much reduced in size, and is no longer
(zygote) is retained in a cone until it is
independent. Seed plants produce two
mature.
kinds of gametophytes: the male
(microgametophyte) and the female
Female gametophyte
(megagametophyte).
Male
gametophyte
sperm
Pollen grain (microspore)
egg
Ovule (megaspore)
What is a Seed?
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A seed is a sporophyte plant embryo
surrounded by a protective seed coat,
which keeps the embryo from drying
out. In addition, seeds often contain a
food supply for the developing embryo.
Seeds have allowed plants to become
adapted to life on land in three major
ways:
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Dispersal — many seeds have
appendages that aid in dispersal
by water, wind, or animals.
Dispersal prevents competition
between parent and offspring.
Nourishment — Most kinds of
seeds have lots of food stored
within them, which provides the
young embryo with an energy
source to begin its growth.
Dormancy — Seeds can lie
dormant for many years,
protecting the embryo from
unfavorable conditions
Evolution of Flowers
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Gymnosperms have not efficiently solved 
the problem of fertilization. Many pollen
grains must be carried by wind in order to
ensure the joining of sperm and egg within
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a female cone.
Angiosperms often have pollen delivered
directly from one individual to another, 
thus greatly increasing the chance of
fertilization. This innovation is made
possible by the evolution of the flower.
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Layers of a
Flower
What is a flower? It is the reproductive
structure of angiosperms. The basic
structure of a flower consists of four
concentric whorls of appendages:
Calyx — outermost whorl, made of
sepals, which are modified leaves, and
protect the bud from damage.
Corolla — next layer, made of one or
more petals, which are also modified
leaves, but produce bright pigments or
strong fragrances to attract animals.
Androecium — produces the
microgametophytes, or pollen grains. This
layer is made of the stamens.
Gynoecium — is the innermost layer of
the flower and consists of one or more
pistils, containing the ovary and ovules.
 Flowers containing all four parts are complete, while flowers missing one or more parts
are incomplete.
Parts of a Flower
Stamen:
Anther
Filament
Petals
Sepals
 The outermost layer of a flower consists of
sepals, which serve to protect the developing
flower parts. Inside of this is the whorl of petals,
which are often brightly colored to attract animals.
 The next layer of a flower
contains the male reproductive
structures. Stamens consist of
two parts: the filament, a
strong stalk, and the anther,
Pistil:
which rests on the filament and
Stigma
produces pollen grains.
Style
Ovary
with
ovules
 The inside layer of a flower contains
the female reproductive structures.
These may be one or more pistils.
The pistil is subdivided into the
ovary, where ovules develop, the
sticky stigma, where pollen lands,
and the style which connects them to
each other.