Evolution of Land Plants

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15/09/11
Evolution of Land Plants
Plants moved from water to land:
- Water is denser and more viscose than air so takes less energy to more
around in
Structural changes in plants to assure success of reproduction in air
Challenge
In Water
In Air
1. Gamete transfer
Gametes released in water
able to unite easily, water is a
conduit
Gametes must be protected
and transfer must be
facilitated gamete
retained in mother plant
2. Dehydration
Cannot happen, surrounded
by water
Dehydration of body can
occur, processes occur in
solution = waxy covering
(cuticle)
3. Support
Water provides buoyancy,
supports plant
Plants must support itself
4. Nutrient
acquisition
Nutrients and water provided
by water around it
Evolution of roots, shoots,
stomata, vascular system to
distribute nutrients
5. Light intensity
Water absorbs energy from
light, low photosynthetic rate
Energy from light is higher,
no limit of photosynthesis =
evolution of big leaves to
maximize process
6. Growth
Limit to growth (cannot grow
out of water)
Apical growth and branching
to achieve maximum growth
Evolution order:
1. Protection of embryos (most important aspect as nothing else would be able
to evolve without the protection of the embryo)
2. Stomata
3. Green sporophyta
4. Tracheids (vascular branching, independent of sporophyte = roots)
5. Megaphylls vs Microphyls
6. Seeds
7. Flowering plants
Alternation of generations:
All organisms have 2 stages in life cycle:
- Haploid phase (gameto phase):
- produces gamete (sperm, eggs) 1N
- gametophyte in plants
Fertilization occurs fusion of gametes
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