• Seeds changedthe course of plant
evolution, enabling their bearers to
become the dominant producers in most
terrestrial ecosystems
• Seed plants originated about 360 million
years ago
• A seed consists of an embryo and nutrients
surrounded by a protective coat
• Seeds can disperse over long distances by
wind or other means
Seeds
3.
• In additionto seeds, the following are common to all seed plants:
• Reduced gametophytes (mostly microscopic)
• Heterospores (two kinds of spores)
• Ovules (female gametophyte)
• Pollen (male gametophyte)
Seeds
4.
PLANT GROUP
Seed plants(gymnosperms and angiosperms)
Reduced (usually microscopic), dependent on
surrounding sporophyte tissue for nutrition
Dominant
Gymnosperm Angiosperm
Microscopic female
gametophytes (n)
inside ovulate cone
Microscopic female
gametophytes (n)
inside these parts
of flowers
Microscopic
male
gametophytes
(n) inside pollen
cone
Microscopic
male
gametophytes
(n) inside
these parts
of flowers
Sporophyte
(2n)
Dominant
Sporophyte
(2n)
Reduced, dependent
on gametophyte for
nutrition
Gametophyte
(n)
Example
Sporophyte
Dominant
Gametophyte
Mosses and other
nonvascular plants
Ferns and
other seedless
vascular plants
Reduced,
Independent
(photosynthetic
and free-living)
Gametophyte
(n)
Sporophyte (2n) Sporophyte (2n)
5.
• The ancestorsof seed plants were likely homosporous, while seed plants
are heterosporous
• Megasporangia produce megaspores that give rise to female gametes
• Microsporangia produce microspores that give rise to male gametes
Heterosporous
6.
• An ovuleconsists of a megasporangium, megaspore, and one or more
protective integuments (covers)
• Gymnosperm megasporangia have one integument/cover
• Angiosperm megasporangia usually have two integuments/covers
Ovule
• Microspores developinto pollen grains, which contain the male
gametophytes
• Pollination is the transfer of pollen to the part of a seed plant containing
the ovules
* Pollen eliminates the need for a film of water and can be dispersed great
distances by air or animals
• If a pollen grain germinates, it gives rise to a pollen tube that discharges
sperm into the female gametophyte within the ovule
Pollen
9.
• A seeddevelops from the whole ovule
• A seed is a sporophyte embryo, along with its food supply, packaged in
a protective coat
Evolutionary Advantage of Seeds
• Seeds provide some evolutionary advantages over spores
• They may remain dormant for days to years, until conditions are favorable for
germination
• Oldest seed germinated, ~2,000 years old!
• Seeds have a supply of stored food
• They may be transported long distances by wind or animals
10.
• Gymnosperms means“naked seeds”
• The seeds are exposed on
sporophylls that form cones
• Angiosperm seeds are found in fruits,
which are mature ovaries
• Most gymnosperms are cone-bearing
plants called conifers
Gymnosperms
11.
• Three keyfeatures of the
gymnosperm life cycle
are:
• Miniaturization of their
gametophytes
• Development of seeds
from fertilized ovules
• The transfer of sperm to
ovules by pollen
• The life cycle of a pine
provides an example
Gymnosperms
12.
• The pinetree is the sporophyte and produces sporangia in male and
female cones
• Small cones produce microspores called pollen grains, each of which
contains a male gametophyte
• The familiar larger cones contain ovules, which produce megaspores that
develop into female gametophytes
• It takes nearly three years from cone production to mature seed
Gymnosperms
• Fossil evidencereveals that by
the late Devonian period (360
mya) some plants had begun to
acquire some features that are
also present in seed plants
• For example, Archaeopteris
was a heterosporous tree with
a woody stem, but it did not
bear seeds
Evolution of Seed Plants
16.
• Living seedplants can be divided into
two clades: gymnosperms and
angiosperms
• Gymnosperms appear early in the fossil
record about 305 million years ago and
dominated Mesozoic (251–65.5 million
years ago) terrestrial ecosystems
• Gymnosperms were better suited than
nonvascular plants to drier conditions
Evolution of Seed Plants
17.
• Gymnosperms servedas food for
herbivorous dinosaurs
• Recent fossil discoveries show that
gymnosperms were pollinated by insects
over 100 million years ago
• Angiosperms began to replace
gymnosperms near the end of the
Mesozoic
Evolution of Seed Plants
18.
• Angiosperms nowdominate more terrestrial ecosystems, though
conifers still dominate in some regions including the northern
latitudes
• The gymnosperms consist of four phyla
• Cycadophyta (cycads)
• Gingkophyta (one living species: Ginkgo biloba)
• Gnetophyta
• Coniferophyta (conifers, such as pine, fir, and redwood)
Gymnosperm Diversity
19.
• Individuals havelarge cones
and palm-like leaves
• These thrived during the
Mesozoic (65-250 mya), but
most of the few surviving
species are endangered
Phylum Cycadophyta
20.
• This phylumconsists of a single living
species, Ginkgo biloba
• It has a high tolerance to air pollution
and is a popular ornamental tree
Phylum Ginkgophyta
21.
• This phylumcomprises three
genera: Gnetum, Ephedra, and
Welwitschia, ~70 species
• Species vary in appearance, and
some are tropical whereas
others live in deserts
Phylum Gnetophyta
22.
• This phylumis the largest
of the gymnosperm phyla
• Most conifers are
evergreens and can carry
out photosynthesis year
round
• Bristlecone pine: ~4,850yrs
old!
Phylum Coniferophyta
Pitch Pine
23.
• Angiosperms areseed
plants with reproductive
structures called flowers
and fruits
• They are the most
widespread and diverse of
all plants
Angiosperms
24.
Angiosperm Evolution
• Angiospermsoriginated at least
140 million years ago and began
to dominate terrestrial ecosystems
by 100 million years ago
• Chinese fossils of 125-million-year-
old angiosperms share some traits
with living angiosperms but lack
others
25.
• The ancestorsof angiosperms and
gymnosperms diverged about 305
million years ago
• Amborella and water lilies are likely
descended from two of the most
ancient angiosperm lineages
Angiosperm Evolution
• The floweris an angiosperm
structure specialized for
sexual reproduction
• Many species are pollinated
by insects or animals, while
some species are wind-
pollinated
Angiosperms - Flowers
28.
• A floweris a specialized shoot
with up to four types of modified
leaves called floral organs:
• Sepals, which enclose the flower
• Petals, which are brightly colored
and attract pollinators
• Stamens, which produce pollen
• Carpels, which produce ovules
Angiosperms - Flowers
29.
• A stamenconsists of a stalk
called a filament, with a sac
called an anther where the
pollen is produced
• A carpel consists of an
ovary at the base and a
style leading up to a
stigma, where pollen is
received
Angiosperms - Flowers
30.
• Flowers thathave all four
organs are called
complete flowers
• Those lacking one or
more organs are called
incomplete flowers
Angiosperms - Flowers
31.
• Flowers mayhave radial
symmetry or bilateral
symmetry
• For flowers with radial
symmetry, any imaginary line
through the central axis divides
the flower into two equal parts
• In bilateral symmetry, a flower
can only be divided into two
equal parts by a single
imaginary line
Angiosperms - Flowers
32.
• A fruitis formed when the ovary wall thickens
and matures
• Fruits protect seeds and aid in their dispersal
• Mature fruits can be either fleshy or dry
• Various fruit adaptations help disperse seeds
• Seeds can be carried by wind, water, or
animals to new locations
Angiosperms - Fruits
33.
• A pollengrain that has landed on a stigma germinates and the pollen
tube of the male gametophyte grows down to the ovary
• The ovule is entered by a pore called the micropyle
• Double fertilization occurs when the pollen tube discharges two sperm
into the female gametophyte within an ovule
Angiosperm Life Cycle
34.
• One spermfertilizes the egg, while the other combines with two nuclei
in the central cell of the female gametophyte and initiates
development of food-storing endosperm
• The triploid endosperm nourishes the developing embryo
• Within a seed, the embryo consists of a root and one or two seed
leaves called cotyledons
Angiosperm Life Cycle
35.
• Angiosperms comprisemore than 250,000 living species
• Previously, angiosperms were divided into two main groups:
• Monocots (one cotyledon)
• Dicots (two cotyledon)
• DNA studies suggest that dicots are paraphyletic
Angiosperm Diversity
36.
• More thantwo-thirds of
angiosperm species are
eudicots
• Eudicots include the large
legume family and the
economically important
rose family (Rosaceae)
Eudicots
37.
• More thanone-quarter of
angiosperm species are
monocots
• The largest groups are the
orchids, grasses, and palms
Monocots
#2 Seed plants originated about 360 million years ago (cultivated 12,000 years ago)
#3 Heterospory: Twi different kinds and sizes of spores. One Megaspore (Female gamete) and one Microspore (Male gamete).
#4 Figure 30.2 Gametophyte-sporophyte relationships in different plant groups
#5 Homosporous: Producing only one kind of spore. Describes species whose sporophytes produce only one kind of spore, each of which germinates to yield a unisexual or bisexual (hermaphroditic) gametophyte.
#6 An ovule consists of a megasporangium, megaspore, and one or more protective integuments(protective sporophyte tissue)
#7 Figure 30.3-3 From ovule to seed in a gymnosperm (step 3). Fertilization initiates the transformation from ovule into seed, consisting of the embryo and its food supply and a protective seed coat. The megasporangium eventually dries out and collapses.
#13 Figure 30.4a-3 The life cycle of a pine (part 1, step 3). Each scale of an ovulate cone has two ovules, each containing a megasporangium (only one shown in this figure). Pollenation occurs when a pollen grain reaches an ovule. The pollen grain then germinates forming a pollen tube that digests its way through the megasporangium.
#14 Figure 30.4b-3 The life cycle of a pine (part 2, step 3). These seeds go on to produce a seedling.
#29 See-pull
Car-pull
Some plants have evolved to have self-incompatibility mechanisms to avoid self-pollination. A physiological barrier makes it difficult or impossible for a flower to fertilize itself even though it may have been abundantly pollinated with its own pollen.
#35 descended from a common evolutionary ancestor, but not including all the descendant groups.
#38 Figure 30.12 The life cycle of an angiosperm. On the anther each microsporangium contains microsporocytes that divide by meiosis producing microscopes. (RIGHT) The microspore develops into a pollen grain, and the generative cell will divide forming two sperm. The tube cell will produce the pollen tube. (CENTER) In the megasporangium of each ovule the megasporocyte will divide by meiosis producing four megaspores. One survives and forms a female gametophyte. (FERTILIZATION) Double fertilization occurs. One sperm fertilizes the egg forming a zygote. The other sperm fertilizes the central cell, forming the endosperm which serves as a triploid food supply. (LEFT) The zygote then develops into an embryo that is packaged along with food in the seed. When the seed germinates the embryo develops into a mature sporophyte.
