The plant kingdom is in the domain
Eukarya and in the supergroup
Archaeplastida
Charophytes and green plants have
in common1. Same cellulose synthesizing complexes
and same cell-wall formation.
2. Apical meristem to increase in length
and produce specialized tissue
3. Both contain plasmodesmata or
poresPlants have adapted to land.
Benefits of living on land
-more light (water reduces light reaching
plants
-more CO2 available for photosynthesis
-more minerals found in land
Disadvantage
-support (water gives more support than
air)
-drying out and obtaining enough water
-reproduction bringing gametes together
and prevent them from drying out
Land plants have evolved adaptations for
each of these problems.
4 Derive Traits of Land Plants
1. Exhibit alternation of generations
producing an embryo that is for some time
dependent upon the female gametophyte.
2. Plants produce spores coated with “sporopollenin” to prevent dehydration.
3. Multicellular gametangia to produce eggs and sperm.
4. Apical meristem- Area found on the tips of shoots and roots and other locations that specialize
in the process of mitosis.
1. Alternation of generations- If the
parental generation is diploid (2n
with two sets of chromosomes) it is
called the sporophyte generation. In
the process of reproduction it will
form sporangia that will have cells
inside that undergo meiosis to
produce haploid spores (1n one set
of chromosomes). They may be of
different sizes-megaspores and
microspores. At that point in time it
becomes the gametophyte
generationThe gametophyte generation is
haploid and produces gametes. In
general the megaspore produces a
gametophyte via mitosis that contains an archegonium that produces an egg. The microspore
produces a gametophyte that contains an antheridium that produces sperm. The gametophyte
and sporophyte generation look nothing like one another.
Over the course of evolution, there has been a trend for the sporophyte generation to become
more conspicuous than the gametophyte generation. Note each generation has a multicellular
organism.
2. Plants produce spores coated with “sporopollenin” to prevent dehydration in multicellular
compartments. Green algae produce their spores in just one cell.
3. Multicellular gametangia to produce eggs and sperm.
4. Apical meristem- Area found on the tips of shoots and roots and other locations that specialize
in the process of mitosis.
In the course of evolution of land plants, major events occurred to include development of
vascular tissue, stems, leaves, roots, seeds and flowers. There are major groupings include
bryophytes, seedless vascular plants and the plants that produce seeds and flowers.
I. Bryophytes are nonvascular land plants. They do have structures that resemble leaves and
roots (rhizoids) but these tissues have no vascular tissue. There are three bryophyte phyla but
they do not form a monophyletic clade. The gametophyte generation is the most conspicuous.
A. Liverworts (Phylum Hepatophyta)-flatten body (thallus) with lobed like shape. Form cup like
structure for reproduction. The gametophyte generation is the most conspicuous generation.
B. Hornworts (Phylum Anthocerophyta)-The gametophyte is leafy, and the sporophyte generation
grows out of the gametophyte generation and is dependent on it.
C. Mosses (Phylum Bryophyta) - are bryophytes over 15,000 species. Usually found in moist
area. Has leaf-like structures and
rhizoids. The archegonia and
antheridia are found at the top of
the gametophyte. Once fertilized
the sporophyte grows out of the
top of the gametophyte forming a
capsule where meiosis and
spores are formed. forming a
capsule where meiosis and
spores are formed.
Phylum Lycophyta-Evolution of
vascular tissue. Two types of
tissue evolvedXylem-moves water and minerals
up and is strengthened with lignin
in cell walls
Phloem moves water and organic
nutrients both up and down.
Also leaves (microphylls only one strand of vascular tissue) and roots evolved as extensions from
the stem. Sporophyte generation conspicuous generation.
Microphylls contain sporangia at the top of the plant in a
strobili.
Three major classes include club mosses, spike mosses and
quillworts.
Club moss with vascular tissue. Microphylls containing
sporangia at the top of the plant. Club moss with vascular
tissue. Microphylls containing sporangia at the top of the
plant
Phylum Pterophyta-Includes ferns, horsetails and whisk ferns
The evolution of megaphylls or true leaves with branched
vascular bundles in the leaf. Allows for increased
photosynthesis. Ferns have underground horizontal stem
(rhizome) and leaves (frond) that push up from the soil. The
gametophyte generation reduced.
The Phylum
Pteridophyta includes
horsetails and whisk
ferns. Horsetails-only
one genus.
Underground rhizome,
that produces aerial
stems with whorls of
side branches. Silica
found in cell walls.
Whisk ferns-lack
megaphylls and roots.
Only branching stems
and root. Seed plantsproduce seeds in the
sporophyte generation.
A seed consist of a
seed coat, food, and
sporophyte embryo. Also spores produced by the
sporophyte generation are retained in the plant and are
not released into the environment. All seed plants
produce two different types of spores (heterospory).
Microspores make the male gametophyte (pollen) and
megaspores make the female gametophyte inside a
structure called the ovule. The female gametophyte
never leaves the sporophyte. The ovule eventually
becomes the seed once the egg of the female
gametophyte is fertilized. Note-sperm cells are not
released into the environment like seedless plants. The
entire male gametophyte is used to deliver the sperm
cells. Seeds and pollen eliminates the necessity of
water for reproduction. Both can be carried long
distances and have a thick coats to resist drying out.
Two major types of seed plants-Gymnosperms and angiosperms. Gymnosperms
produce naked seeds (ovule not complete enclosed in sporophyte tissue). Does not produce fruit
or flowers like angiosperms.
Gymnosperms
Conifers-Large gymnosperm group 575
species most do not shed their leaves
in the fall. Includes pine tree, junipers
and sequoias. It takes 2 yrs to produce
a seed.
Phylum Cycadophyta-cycads have
large cones and palmlike leaves.
Phylum Ginkgophyta-only one species
surviving. Deciduous fan leaves with
fleshy seeds.
Phylum Gnetophyta-species are found
in tropics and desert and varies greatly
in morphology.
Phylum Anthophyta-Flowering plants
Characteristics-flowers and the
production of seeds. Most successful
plant phylum. A flower is a structure
specialized for reproduction.
1. Sepal-leaf like and protects the floral bud.
2. Petals-Usually showy with colors to attract
pollinators
3. Stamen-male reproductive organ. Contains an
anther where male gametophytes or pollen is
produced. The anther sits long stalk called the
filament, which connects to the base of flower
4. Carpel-female reproductive
organ. The swollen bottom or
ovary contains one or more ovules
where the female gametophyte is
found. The ovary connects to a
slender structure called the style.
At the top of style is the stigma where the pollen lands. A flower may have
multiple carples or only one.A flower can have both male and female
reproductive organs. If it does, it is termed perfect but if it does not it is termed
imperfect. Male flowers are called staminate flowers and female flowers are
called carpellate flowers. If both flowers are on the same plant, then the plant is
said to be monoecious but if they are on different plants (male date palms vs.
female date palms), then the plant is dioecious. Corn is a monoecious plant with
staminate and carpellate flowers on the same plant. Sagittaria is dioecious. The
plant on left is male and the right female.
Microgametogenesis-In the anther chambers there are microspore mother cells (2n). They
undergo meiosis to produce 4 microspores (n). The microspores undergoes mitosis to produce a
spore with two nuclei, one becomes the tube cell and the other the generative cell. The
generative cell will undergo mitosis once more to make two sperm nuclei. This is the male
gametophyte. The male gametophyte will form a very drought resistant pollen grain. The shape
is species specific.
Megagametogenesis-Is the formation of the female gametophyte. Inside the ovary, there are one
or more ovules. Each ovule has a megaspore mother cell (2n). This cell will undergo meiosis to
produce 4 megaspores (n). Three of cells will degenerate but one will survive to give rise to
female gametophyte. The megaspore (n) will under-go three mitotic divisions without cytokinesis
to give rise to eight nuclei. Division of the cytoplasm will then occur. It will produce seven cells.
Three on each end and one in the middle.
Pollination and fertilizationOnce a pollen falls on the stigma of the carpel, the pollen begins to
digest the neck of the style and sending down a pollen tube. This pollen
tube will have the tube nucleus in it. It will be followed by the generative
nucleus which will undergo mitosis to form 2 sperm nuclei. The pollen
tube is making its way to ovule which is housing the female
gametophyte. There is an opening in the ovule called the micropyle.
The pollen tube sends one sperm nucleus to fertilize the egg, and the
second to fertilize the polar
nuclei or large central cell.
This cell becomes triploid
(3n) and is called
endosperm. This is a case
of double fertilization. The
fertilized egg or zygote will
give rise to the seed
embryo; the endosperm will
provide nutrients to the
embryo. The ovule will
become the seed coat. The ovary under the
influence of hormones will become the fruit of the
plant. The fruit or pericarp of the plant is used to
protect enclosed seeds and aids in their dispersal.
. The two groups of flowering plants are the monocots and eudicots (formerly dicots)