Transcript Plant Diversity I: The Colonization of Land

Plant Diversity II:
The Evolution of Seed Plants
Campbell, 5th Edition, Chapter 30
Nancy G. Morris
Volunteer State Community College
Evolution of Seed Plants


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Gametophytes of seed plants continue
pattern of reduction
Sporophytes continue pattern of
dominance
(Figure 30.1)
Reproductive Adaptations of Seed Plants
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Gametophyte develops
within the spore retained
in the tissues of the
parent sporophyte.
(Figure 30.1)
Trend in Dominance of Sporophyte
Reproductive Adaptations of Seed Plants
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
The seed replaced the spore as the main
means of dispersing offspring.
(Figure 30.2)
The seed, which is the fertilized ovule,
consists of a sporophyte embryo packaged
along with a food supply within a seed
coat.
Figure 30.2
From Ovule to Seed
Reproductive Adaptations of Seed Plants
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
Pollen became the vehicles for sperm cells in
seed plants.
The pollen grain, which is the immature male
gametophyte, can be dispersed through the
air by wind or transported by animals.
Gymosperms
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Bear their seeds “naked” on the surfaces
of sporophylls.
Pine Life Cycle -- key reproductive
adaptation of seed plants (Figure 30.4)
–
–
–
1) Dominance of the sporophyte
2) Development of seed from
fertilized ovules
3) Flagellated sperm replaced by
pollen
4 Divisions of Gymnosperms
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Division Cycadophyta – sago palms

Division Ginkgophyta – ginkgo
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Division Gnetophyta – Welwitshia
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Division Coniferophyta – pines, firs,

(Figure 30.3)
redwoods, spruce, hemlock, bald cypress
Figure 30.4
Gymnosperm
Life Cycle
Angiosperms

Terrestrial adaptation continued with the
refinement of vascular tissue
– both xylem vessel elements & fibers
evolved from tracheids, a type of
xylem. (Figure 30.5)
Figure 30.5
Tracheids
Angiosperms

The flower is the defining reproductive
adaptation (Figure 30.6)
– Sepals, petals, stamens (which produce
pollen), carpels (which produce ovules),
are whorls of modified leaves that
make up flowers.
Figure 30.6
Flower
Anatomy
Angiosperms

Fruits help disperse the seeds of
angiosperms (Figure 30.7)
– Ovaries ripen into fruits,
which when opened disperse
seeds to new locations.
Life Cycle of the Angiosperm
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Alternation of Generations Life Cycle
Figure 30.8
Double fertilization occurs when a
pollen tube discharges two sperm into
the embryo sac (the female
gametophyte within an ovule). One
sperm fertilizes the egg, the other
combines with two nuclei to produce
the food-storing endosperm.
Figure 30.8
Life Cycle of Angiosperm
Consider this…

Angiosperms & animals have shaped
one another’s evolution.
–
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Pollination of flowers by animals &
transport of seeds by animals are two
important relationships in terrestrial
ecosystems.
Agriculture is based almost entirely
on angiosperms.
–
Human cultures depend on the cultivation
& harvest of angiosperms, especially the
fruits of grains.
Consider this…

Plants transform the atmosphere and the
climate.
–
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By lowering the concentration of CO2, plants
probably contribute to the cooling of the Earth.
Plants are a renewable resource.
Plant diversity is a nonrenewable resource.
–
Destruction of the tropical rainforests is an
especially urgent problem because they contain
the greatest diversity of plants on Earth.
Embryological
Development
of a Plant