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Kingdom
Plantae,
Continued
Sexual
sperm + egg  zygote
Asexual
spores and runners
(man can use grafts
and cuttings)
Alternation Of Generations
All plants have a life cycle that
involves two alternating stages- a
diploid,(2n), sporophyte stage and a
haploid, (1n), gametophyte__ stage.
1n = means it has half the usual chromosome
number
2n = means it has the full chromosome number
Moss and Ferns have similar life
cycles, yet there are a few
differences.
*are small, low-lying, (generally) moisture-loving plants
*have no roots, only filamentous rhizoids (so, they are a
good example of a NONVASCULAR plant. ).
The dominant generation is the 1n gametophyte. The 2n
sporophyte is actually parasitic on the gametophyte.
* Needs water for sexual reproduction; sperm must swim
to egg
MOSS MOVIE
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
sporophyte (2n)
gametophyte (n)
Pterophyta (Ferns)
About 97% of living seedless,
vascular plants are ferns.
In fact, there are probably
about 12,000 species of
ferns in the world, most
of these are found in the tropics.
The ferns are highly
successful and are virtually
found in any habitat
flowering plants are found.
Ferns
In ferns, as in other
seedless, vascular
plants, the sporophyte
is the dominant
generation. The
gametophyte is shortlived, a few mm in
size, and virtually
hidden from view.
Two features of ferns
especially stand out:
Large, typically pinnate, leaves often termed fronds.
The protective coiling of young
fern leaves into a spiral like a
shepherd's crook or a
fiddle head.
Ferns typically have a horizontal
(often underground) stem or rhizome,
swollen with food reserves, from which the leaves
and roots arise.
Some ferns, rather than having spores
on the underside of all of their leaflets,
have separate specialized
spore-bearing (fertile) leaflets
and separate photosynthetic,
sterile leaflets. A Caribbean example
of this is the "flowering fern",
Anemia adiantifolia, shown at right.
FERN MOVIE
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
Similarities =
1. The gametophyte stage produces an egg and sperm
through a type of cell division called mitosis.
2. An egg and sperm unite to form a zygote which
develops into a sporophyte.
3. Moisture is needed in order for the sperm to swim
to the egg to fertilize it.
4. The sporophyte stage produces spores through a
type of cell division called meiosis.
Main difference = The gametophyte stage in
the moss is much larger than its sporophyte
stage. While in the fern, the sporophyte stage
is so
large that it crushes the
gametophyte (which is only10 mm, one-
ws.
half of an inch) as it gro
Seed Plants
Angiosperms - flower and fruit
producers
Gymnosperms - cone producers
Gymnosperms
The
include the oldest and largest trees known.
The Bristle Cone Pines, some over 4000 years old are the oldest living plants.
The Giant Redwoods are over 100 m tall - the tallest plants known.
Both are native to California.
Cycads (A type of gymnosperm)
Gymnosperms are Cone producers.
Their seeds are considered to be
“naked” or not protected by a fruit.
The cycads are ancient gymnosperms
which were at their peak in the Jurassic Period,
the "Age of the Dinosaurs", about 150 million years ago.
Phylum Coniferophyta
(The Conifers)
The conifers form the dominant climax
vegetation in cold regions. They have a world
wide economic importance as a source of timber
and pulp for paper.
Conifer features
Their leaves are simple (not-pinnate), highlyreduced, and generally evergreen = needles.
Male & female reproductive organs borne in
cones (conifer means bearing cones)
Male reproductive organs
The male cone or microstrobilus contains the pollen. The pollen
contains the microgametophytes (the “sperm).
Male cones are
short-lived,
shedding their
pollen in the spring,
then withering and
dying. Female
cones are longlived.
Female reproductive organs
The female cone (megastrobilus) is a spiral cluster
of scales each bearing 2 ovules
(megagametophytes). The ovules are exposed to
the air.
There is a period of 1 year between pollination and
fertilization and up to a further year before
maturation and release of the seed.
1st year female pine cones
2nd year immature female pine cones
2nd year mature
female pine cones
Flowering Plants
The flowering plants or Angiosperms
emerged in the Cretaceous period,
some 130 million years ago.
Angiosperm means "contained seeds”
The ovules, which after fertilization mature into seeds,
are found and protected within structures called carpels
within the ovary of the flower. So, unlike the previous
seed plants examined, the ovules are protected within
these carpels and the seeds later sealed within a fruit.
So, a fruit is the ripened ovary of a flower!!!!!!
(see handout on “Life Cycle of an Angiosperm”)
And, a flower is nothing
more than a cluster of
gamete-bearing leaves
surrounded by whorls
of protective and often
very beautiful leaves.
Fruit Remember, a fruit is the ripened ovary of a flower
which contains the developing seeds (fertilized ovules).
The botanist's definition of a fruit
often differs from the lay person's. Fruit are not
necessarily sweet and juicy. They can be dry and
woody. Tomatoes and cucumbers are fruits
even if to the average person
they are vegetables.
Incompatibility mechanisms A pollen tube must grow through the
carpel to get to the ovule (unfertilized egg).
As a result, a range of incompatibility mechanisms
have evolved to control what pollen grain is allowed
to germinate on the stigma, what pollen tubes are
permitted to grow through the style, and ultimately
what male gamete will fuse with the egg.
Unique double fertilization One sperm fuses with the egg to form
the zygote which develops into a
miniature plant, the embryo.
A second sperm (“male” nucleus)
fuses with two polar nuclei to form a
triploid endosperm (orange at right)
which develops simply as a food
reserve for the developing embryo
(red at right).
[Coconut water is actually a liquid
endosperm which helps to feed the
young embryo in the coconut fruit!]
In summary, Angiosperms:
Like all seed plants, the sporophyte is the dominant generation.
and the gametophyte has been internalized (endospory).
The complete enclosure of the ovules by the carpels has led
to the evolution of mechanisms which prevent certain types of
pollen access to the ovules.
Double fertilization, in which both male gametes in the pollen
tube are functional, is unique to the Angiosperms.
The further development of the ovary of the flower to produce a
structure to aid in the dispersal of the seed(s) - the fruit is also unique to Angiosperms.
More on those Angiosperms
Phylum - Anthophyta
Class Monocotyledones
Class Dicotyledones
The Monocot-Dicot Divide
All (well, the vast majority of!) flowering plants fall neatly into two categories the Monocotyledons and the Dicotyledons. These names come from the number
of seed leaves or cotyledons (1 or 2) on the embryo in the seed but there are other
major differences:
Monocotyledons
Flower parts in 3's or multiples of 3
Leaves parallel-veined
Stem vascular bundles scattered
No secondary growth - no true trees!
Fibrous rooted
Corn
Dicotyledons
Flower parts not usually in 3's
or multiples of 3
Leaves net-veined
Stem vascular bundles in a ring
Secondary growth - many woody plants
Tap-rooted
Sunflower
Cotyledon - seed leaf
in a plant
embryo
Monocots - 1 cotyledon, flower part
in 3’s
Dicots - 2 cotyledons, flower
parts in 4’s or 5’s