Transcript BIO509 Lecture # 18 File

School of Sciences, Lautoka Campus
BIO509 Botany Lecture 18:
Angiosperms
Photo courtesy of Prof. Randy Thaman
Angiosperms
• Commonly known as “flowering plants”.
• Produce the reproductive structures called flowers & fruits.
• Extremely diverse: approximately 250,000 known species
(compared to 720 gymnosperm spp.)
• 90% of land plant
species.
Angiosperms originated approximately
140 mya.
Occur in a single phylum – Phylum
Magnoliophyta (previously known as
the Anthophyta.
By comparing the genes that give rise
to flowers & cones, scientists
hypothesize that flowers evolved from
the pollen-producing reproductive
structures of a gymnosperm ancestor.
Change from a
gymnosperm and
fern
dominated world to
a world
dominated by fastgrowing
angiosperms was
one of the most
important changes in
the history
of earth.
Which group of gymnosperms
is most closely related to
angiosperms?
Learning outcomes
• Know the similarities and difference between
angiosperms and gymnosperms.
• Understand the major trends of specializations in
flowering plants
• Know the reproductive structures and lifecycle of
a flowering plant.
• Know the characteristics of flowers associated
with specific types of pollinators.
Angiosperms
• Are flowering plants that form seeds inside a protective
chamber called an ovary.
Greek words
“angeion” – vessel
“ sperma” – seed
• “Vessel” is the carpel which is like an inrolled leaf with seeds
along its margin.
Primitive flowers had ovules on the edge of the leaf-like sporophyll. Through
evolution, the edges of the carpel gradually rolled in and fused to enclose the
ovules.
General characteristics of angiosperms
• The flower is the defining reproductive
adaptation of angiosperms.
• Flowers are made up of four types of modified
leaves- sepals, petals, stamens, and carpels.
• Stamens are the male reproductive organs that
produce microspores.
• Carpels are female reproductive organs that
produce megaspores.
General characteristics of angiosperms
• Angiosperms (except
Amborella which is a
primitive flowering plant)
have xylem with both
tracheids and vessel
elements for conduction,
as well as fiber cells for
support.
• In gymnosperms, the only
cell type found in xylem
tissue is tracheids.
Review of Flower Structure
• Sepals (infertile) – enclose & protect
the floral bud.
• Petals (infertile) – attract pollinators.
• Stamen (fertile) – made of a filament
(stalk) & anther (site of pollen
production).
• Carpel (fertile) – consists of a stigma
(pollen landing site), style, & ovary
(location of ovules).
• All floral organs attached to the stem
at the receptacle.
How does this differ from the
reproductive structures of the
gymnosperms?
Floral Variations
• Complete vs Incomplete flowers
– all 4 basic floral organs present =
complete flower
– 1 or more floral organs absent =
incomplete flower
- Flowers can be sterile, female
(carpellate), male (staminate)
- Creates monoecious &
dioecious plants
Complete flower
incomplete flower
Hibiscus is a complete flower (has all 4 basic floral
organs)
Grass flower is incomplete (lacks petals)
Why might petals
be unimportant for
grasses?
Floral Variations
• Bilateral vs. radial symmetry
Floral Variations
• Superior, semi-inferior, or inferior ovary position
Floral Variations
• Individual or clustered flower distribution.
- clusters are called inflorescences
• other: size, shape, color, odor, arrangement
of floral organs
Reproduction in angiosperms
• Are heterosporous like the gymnosperms.
• Sporophytes are the most dominant.
• Female gametophyte is wholly enclosed within
the sporophyte tissue and reduced to only a few
cells.
• Male gametophyte consist of a pollen grain with
three nuclei.
Male Gametophyte = Pollen
Grain
• Develop within
microsporangia located
in anthers.
• Diploid cells within
microsporangia divide
by meiosis to produce
microspores.
Microspores develop
into pollen grains
Pollen grains
become mature
gametophytes when
the generative
nucleus divides &
forms 2 sperm
(usually occurs postpollination)
Female Gametophyte =
Embryo Sac
• Develop within
megasporangia located
within ovules.
• Each megasporangium
contains 1 large diploid
cell that divides by
meiosis to produce 4
haploid cells but only one
survives (megaspore).
The megaspore divides 3
times by mitosis producing
a large cell with 8 haploid
nuclei (four at each end).
One from each migrates to
the centre and forms the
polar nuclei.
Antipodal and synergid cell
have no apparent function
and degenerate.
One cell functions as the
egg (closest to microphyll)
Pollination
• Transfer of pollen from an
anther to a stigma.
• When successful, pollen
grain produces a pollen
tube which grows through
the style to the ovary
where it releases two
sperm into the embryo sac.
Pollination is brought
about by insects, wind,
water, birds, bats,
and other mammals.
Flowers are specially
adapted to attract and
accommodate the
pollinating agents.
Questions??