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Wondrous Events in Evolution. Notes for Plant Taxonomy Biology 4420 at Utah State University Prepared by M.E. Barkworth. Factors important to success. Aspects of life to consider: Nutrition Reproduction Competition Cost/benefits of structures and strategies. - PowerPoint PPT Presentation
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Wondrous Events in Evolution
Notes for Plant Taxonomy
Biology 4420 at Utah State UniversityPrepared by M.E. Barkworth
Factors important to success
Aspects of life to consider: Nutrition Reproduction Competition Cost/benefits of structures and
strategies
For dominance, it is not enough to be good – one must be better than one’s competitors
For survival, it is enough to be better than or as good as one’s competitors in some situations.
Land plants 450 MYBP First evidence of land
plants Cutin, stomates,?mycorrhizal
partnerships Bryophytes and tracheophytes
more or less simultaneous (give or take a million years or so)
Tracheophytes Diploid life style
Backup system in place
Tracheids More cellulose, lignin Benefits outweigh
costs
Megaphyllous leaves Microphyllous leaves
One vein No axillary branches No leaf gaps Restricts shape, size
Megaphyllous leaves Better transportation Diverse shapes Leaf gaps so less
expensive Benefits outweigh
costs
microphyllousleaves
megaphyllousleaves
Tracheophytes can be tall … What’s the advantage?
Sex at ground level so no still restricted Sex requires water so still restricted
A film of water is adequate Chemical guidance system works well
Gametophytes independent, need moisture and nutrition source (soil) so still restricted
The solution is …. Ovules and pollen grains
Ovule provide food and protection for female gametophyte
Pollen grain protects the wandering male gametophyte
Still have to get the two together Once fertilized, the ovule starts to
become a seed
Seeds 1 Integumented
Protective cell layers Integument(s) diploid
Indehiscent Does not split
Megasporangium Where female spores
form and make megagametophyte which makes female gamete, aka egg
Seeds 2 Megasporangium produces
Megaspores which form megagametophyte which forms egg (female gamete)
Other cells of gametophyte provide nutrition – endosperm
Megasporangium wall forms nucellus Megasporangium is surrounded by diploid
tissue (integument) with vascular connection to parent
Integument displays great diversity (think seed coat)
Seeds 3 Advantages
Place genetically vulnerable phase, gametophyte, in protected surrounding
Provide great environment for that difficult event – mixing of DNA from parents
Great place for children to start life Problem: How does male gamete get
there?
Solution - Pollen Grains
Armored airship for male gametophyte
Armor is sporopollenin Meiosis in microsporangia
forms first cell of microgametophyte
Male gametes develop through mitotic divisions in microgametophyte
Dispersal Initially wind Eventually insect Some water
Seed and Pollen Grain Sex above ground level Adequate moisture from female
parent Eventually reduction number of
cell divisions and time in gametophyte phase for both males and females
New problems Bringing the male and female
gametes together Watch for new developments
as plants solve this problem “Educating” wind Educating animals
Back to being tall Wood is energetically expensive Need to minimize cost, maximize
benefit Fibers, the strong part of wood,
primarily associated with vascular bundles
Organization of vascular tissue important
Vascular Tissue Organizationhttp://www.botany.hawaii.edu/faculty/webb/BOT311/Transition/invasion_landStele.htm
Rod Cylinder Scattered Circle, aha! Circular cambium “Good Wood” has circle
of vascular bundles that subsequently are united by cambium which form xylem on inside and phloem on outside
Important but Extinct Groups• Progymnosperm
s (370 MYBP) 35 million years 12 m tall Had “good wood”,
fernlike foliage and reproduction
Important but Extinct Groups
Pteridosperms Seeds Fern like leaves Some had “good wood”
Cycads, Pinophytes, Gnetophytes, Angiosperms may have evolved independently from different groups of pteridosperms.