Seed Plants

1
Seed Plants
2
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?
3

• 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
4
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? What problems did these innovations solve?
Cycads
5
Proposed phylogeny of land plants(review)
Wood
and pollen
Leaves
(some Pteridophytes)
waxy cuticle and protected gametes
6
Three reproductive modifications contributed to
the success of seed plants

• Sporophytes of seed plants do not release their
  spores. Therefore, the small gametophytes are
  protected and develop within the sporophyte.
• Plants were no longer tied to water for
  fertilization with the evolution of pollen.
• 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

Both female spores and developing embryos were
protected from drying and UV radiation.
7
Secondary Growth (wood)
Fig 35.21

• growth in circumference
• increased support

Compare the typical height of bryophytes, ferns
and conifers.
8
GymnospermsPhylumConiferophyta (conifers)
female cones
male cones

• Coniferata dominate our biomes
• Well adapted to cold dry summers
• naked seeds (no fruit)
• Two kinds of cones
• Male produce spores that grow into pollen grains
• Female produce spores that grow into ovules

Pinus ponderosa
What are the functional names for male and female
cones?
9
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 dont
we see many hybrids?
10
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?
11
Gymnosperm Life Cycle

• vascular
• diploid dominant
• heterosporous
• nonmotile gametes
• naked seeds
• not water dependent

12
Angiosperms

• The most diverse and geographically widespread of
  all plants
• _at_ 250,000 angiosperm species as compared to 720
  gymnosperm species
• Many benefits to humans and other animals
• beauty, food, building materials, medicines, etc.
• Fascinating examples of co-evolution with animal
  species

13
Angiosperm Advantages

• improved vascular system
• 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

14
Pollen Dissemination
Fig. 30.18
15
Seed Dispersal
16
Angiosperms

• vascular
• diploid dominant
• heterosporous
• nonmotile gametes
• seeds
• not water dependent