Transcript Seed Plants - Home | Western Washington University

Seed Plants
Review…
• A green alga is the most likely ancestor to
land plants
• Imagine life in a shallow, temporary pond
How could you resist drying conditions?
Adaptations to shallow water
may have “set the stage” for
the invasion of land…
– waxy cuticle
– protection of gametes
– protection of developing
embryos
The selective advantages of
invading this new habitat…
– less competition for sunlight
unfiltered by water
– mineral-rich soil
– no terrestrial herbivores
during the “honeymoon”
Fig. 29.15 Bryophytes
Recall these themes
in the study of life…
• All things depend
directly or indirectly
on all other living
things for survival.
• There is a struggle for
existence.
What reproductive and other
innovations allowed certain plant
species to dominate the earth?
Cycads
What problems did these innovations
solve?
Proposed
phylogeny
of land
plants
(review)
Wood*
…and pollen
Leaves
…waxy cuticle and
protected gametes
*(some Pteridophytes)
Three reproductive modifications
contributed to the success of seed plants:
1.
Sporophytes of seed plants do not
release their spores. Therefore, the
small gametophytes are protected
and develop within the sporophyte.
Both female spores and developing
embryos were protected from drying and
UV radiation.
2. Plants were no longer tied to water
for fertilization with the evolution
of pollen.
3. Embryonic sporophytes are
packaged within seeds.
•
•
The seed replaces the spore as the
main means of dispersal
The embryo within the seed is
protected by the seed coat, and
nourished by parental tissue
Fig 35.21
Secondary
Growth
(wood)
• growth in
circumference
• increased support
Compare the typical
height of bryophytes,
ferns and conifers.
Gymnosperms:
Phylum
Coniferophyta
(conifers)
female cones
male cones
• Coniferata dominate our biomes
Pinus ponderosa
• Well adapted to cold & dry summers What are the functional
names for male and
– “naked seeds” (no fruit)
female cones?
– Two kinds of cones
• Male produce spores that grow into pollen grains
• Female produce spores that grow into ovules
Pollen
(Gymnosperms)
• Outer layer of pollen is made
impermeable by “sporopollenin”
– winged for wind dispersal,
– lots of pollen is produced, and
randomly reaches receptive
ovules within female cones.
Lodgepole pine
Pinus contorta
How does the evolution of wind-born male gametes (pollen)
affect gene flow?
If pollination is more likely and more random by this method,
why don’t we see many hybrids?
Gymnosperm seed development
Identify the male and female
gametophytes in the figure below.
What function is the seed coat providing
as demonstrated in this photo?
Gymnosperm Life Cycle
•
•
•
•
•
•
vascular
diploid dominant
heterosporous
nonmotile gametes
naked seeds
not water dependent
• The most diverse and geographically
widespread of all plants
– @ 250,000 angiosperm species as
compared to 720 gymnosperm species
Angiosperms
• Many benefits to humans and other
animals
– beauty, food, building materials,
medicines, etc.
• Fascinating examples of co-evolution
with animal species
Angiosperm Advantages
• improved vascular system
anther
• pollen in anthers
…results in the potential for
diverse dissemination of pollen
• ovules are reduced in form
and are completely
surrounded by integuments
…results in the potential for
diverse disbursement of seeds
ovules
Pollen Dissemination
Hummingbird
“floral tubes”
red flowers
Baobab tree
night pollinator
Scotch Broom...
anthers “swing” up to
brush bee’s back.
Fig. 30.18
Seed Dispersal
wind
carried
Angiosperms
•
•
•
•
•
•
vascular
diploid dominant
heterosporous
nonmotile gametes
seeds
not water dependent