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Plant Evolution Ch21
Students should be able to:
• List the four major plant divisions
• Define the plant life cycle of alternation of generations
• Name which stage is dominant for each plant division (gametophyte or sporophyte)
• List the key terrestrial adaptations for each plant division.
• Name the parts of a flower
Figure 14.25
What is a plant? • Multicellular, photosynthetic eukaryote that
typically lives on land
• Has cell walls made of cellulose
Plants evolved from green algae • The algal ancestors of plants carpeted moist
fringes of lakes or coastal salt marshes
• First moved to land over 500 million years ago
• Charophytes: Closest relatives to land plants
© 2013 Pearson Education, Inc.
Plants vs. Algae
(Adaptations to
their environments)
Leaf performs photosynthesis
Cuticle reduces water loss; stomata regulate
gas exchange
Shoot supports plant
Surrounding water supports
the alga
Whole alga performs photo-
synthesis; absorbs water,
CO2, and minerals from the
water
Alga
Plant
Figure 21-2 p346
Plant life cycle: Alternation of
Generations
Figure 21-3 p347
Plant diversity reflects evolutionary
history (adaptations to life on land)
© Cengage Learning 2015
1 – Bryophytes
(Non-vascular plants)
• No vascular tissue, lack support, flagellated
sperm require water
• Least adapted to life on land
Figure 21-4a p348
In bryophytes, the gametophyte is
dominant
Gametophyte
(Dominant, carpet-like
form)
Sporophyte
(Reduced and not
independent)
Figure 16.8
© Cengage Learning 2015
Peat moss (Sphagnum)
Cutting blocks of
peat in Ireland for
use as fuel. Peat is
the compressed,
carbon-rich
remains of
Sphagnum moss.
© Cengage Learning 2015
2 – Seedless Vascular Plant
• Vascular tissue with lignin enables plants to
grow tall and upright on land
• Still dependent upon water for reproduction
Fern (Pterophyte)
Figure 21-8 p350
In ferns (and all other groups besides
bryophytes), the sporophyte is dominant
© Cengage Learning 2015
Seed Plants
• 90% of living species
• Adaptations for success:
– Seed is survival packet for embryo
– Pollen (no water required!)
© Cengage Learning 2015
How a seed forms
© Cengage Learning 2015
3 -- Gymnosperms
• “Naked seed” – seeds do not develop in
specialized chamber (no fruit)
Cycads
Conifers
Figure 21-12 p354
A pine tree is a sporophyte with the
gametophyte in its cones
© Cengage Learning 2015
4 – Angiosperms
(Flowering Plants)
• Complex reproductive structures (flowers
and fruit)
Apple blossoms and
fruit
Figure 21-14 p356
Structure of a typical flower
© Cengage Learning 2015 Figure 21-15 p356
An angiosperm plant is a sporophyte
with gametophytes in its flowers
Fruits: Adaptations that help disperse seeds
Wind-dispersed seeds
Fruits: Adaptations that help disperse seeds
Hitchhikers: seeds carried by
animals
Fruits: Adaptations that help disperse seeds
Seeds within edible fruits
Key Haploid (n)
Gametophyte
(n) Sporophyte
(2n)
Sporophyte (2n)
Gametophyte
(n)
Gametophyte
(n)
Sporophyte
(2n)
Diploid (2n)
Seed plants have a greater development of the diploid
sporophyte compared to the haploid gametophyte
generation.
Comparison of alternation of generations
Seed plants Ferns Mosses
The Beauty of Pollination – Moving Art
• Moving Art
Figure 16.UN08
Origin of gametangia
(protect gametes
and embryos)
Origin of vascular
tissue (conducts water and nutrients)
Origin of seeds (protect
embryos from dessication and other hazards)
Origin of flowers (bear ovules
within protective chambers called
ovaries)