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PLANT EVOLUTION
Evolutionary Trends
Bryophytes
The rise of the vascular plants
The rise of the seed plants
KINGDOM PLANTAE

General features:
Eukaryotic, multicellular, photosynthetic autotrophic
organisms
 P.S.= H2O + CO2+ sunlight  oxygen + sugar
 C.R. = sugar + O2  CO2 and H2O + NRG


Origins = blue-green bacteria  ancestral green
algae  algae bryophytes  tracheophytes
THE PHYLA

Phyla grouped into:
- Nonvascular
plants (lack true
(lignified) vascular
tissue)
- Seedless vascular
plants (true vascular
tissue (phloem and
xylem), but reproduce
only by spores (no
seeds made)
- Seed bearing
vascular plants
FERNS
CONE BEARING PLANT
FLOWERING PLANT
SETTING THE STAGE

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Earth’s atmosphere was originally
oxygen free
Ultraviolet radiation bombarded
the surface
Photosynthetic cells produced oxygen and allowed
formation of protective
ozone layer
PIONEERS IN A NEW WORLD

Cyanobacteria were probably first to produce oxygen

Later, green algae evolved and gave rise to plants
ADVANTAGES AND DISADVANTAGES
OF LIFE ON LAND
Advantages:



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Sunlight unfiltered by
water and plankton
Atmosphere had more
CO2 than water
Soil was rich in mineral
nutrients
Originally relatively few
herbivores and
pathogens
Disadvantages:
Relative scarcity of
water
 Lack of structural
support against
gravity

EVOLUTIONARY TRENDS IN PLANTS
STRUCTURE:
Plants came from the sea which support, keep temp
constant, bath whole plant with nutrients
Adaptations to terrestrial Life =

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Roots to anchor and absorb
Conducting vessels xylem & phloem to carry
nutrients up and glucose around VASCULAR
TISSUE
Stiffening ligin to support the plant
Waxy cuticle on leaves and stem to prevent
evaporation
Stomata pores in leaves to allow gas exchange, but
close to prevent water loss
EVOLUTIONARY TRENDS IN REPRODUCTION:


Algae reproduce in water so gametes are carries
by water, form zygotes in water and disperse in
water. Ie No protection from dehydration
required
Land plants needed:
Transport gametes (pollen, flowers)
 Protection from drying out (seeds)
 Dispersal (seed coats & fruits)

EVOLUTIONARY TRENDS IN PLANT LIFE CYCLES:

Alternation of Generations = haploid gametophytes
produces sex cells by mitosis. Gametes unite to from
a diploid zygote, which develops into diploid
sporophyte that develops haploid spores by meiosis
HAPLOID TO DIPLOID

Gametophyte


Sporophyte


Haploid gamete producing body
Diploid product of fused gametes
Spore

Resting structure
The most recently evolved groups produce seeds and
pollen grains which were the key innovations that
allowed the seed plants to spread widely into diverse
habitats.
zygote
EVOLUTIONARY TREND
Relative size
Life span
GREEN ALGAE
BRYOPHYTE
FERN
GYMNOSPERM
ANGIOSPERM
GENERAL TREND = DECREASED SIZE, DURATION, AND
PROMINENCE OF GAMETOPHYTE GENERATION RELATIVE
TO SPOROPHYTE
Algae = some have no sporophyte or only the
zygote
 Mosses = gametophyte is green leafy and
sporophyte is small and short lived
 Ferns = sporophyte is the fronds of the ferns,
gametophyte is smaller yet independent
 Seeded plants = male and female gametophytes
are microscopic and produce gametes to form
sporophyte
embryo

Recall: evolution occurs because of advantageous
traits being selected therefore what is the
advantage of diploid sporophyte dominance?
SPOROPHYTE
The generation in the life cycle of a plant that
produces spores.
 Is diploid but its spores are haploid.
 Either completely or partially dependent on
the gametophyte generation in mosses and
liverworts, but is the dominant plant in the
life cycle of clubmosses, horsetails, ferns
and seed plants.

LE 29-9D
Polytrichum
commune,
hairy cap
moss
Sporophyte
Gametophyte