ECOL 170C1 Lecture Notes - Lecture 9: Pollen, Conifer Cone, Pollen Tube

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DIV. OF LIFE LECTURE 9
Time frame of plant evolution-
earth=4.5 billion y.a.
Life (bacteria=3.5 billion y.a.
Atmosphere becomes oxygenated=2.3 billion y.a.
Driven by cyanobacteria, not plants
Green algae=~1.5 billion y.a.
Land plants=0.5 billion y.a
Angiosperms are only about 140 million y.o. But include about 86% of all plant
species (~300k-350k species)
Graphs show that non-angiosperm plants (ferns, cycads, lycopods) became
diverse about 300 million y.a. And dominated until about 125 million y.a.
Angiosperms took over world 100 million y.a. And non-angiosperms now have
reduced species numbers
Different biomes-
Carboniferous forest
~300 mill y.a. Dominated by ferns and lycopods
Jurassic forest
~200 mill y.a. Dominated by gymnosperms (conifers) and ferns
How did angiosperms take over-
What are differences:
Angiosperms have flowers
Angiosperms make fruit
Gymnosperm sex-
Sporophyte (diploid stage) is dominant
Makes both male cone (pollen cone) and female cone (ovulate cone)
Pollen spreads between plants via wind or insects
Ovulate cone produces haploid egg
Pollen grain produces sperm that fertilizes egg
Zygote develops into embryo surrounded by seed coat (seed drops out of cone
onto ground)
Angiosperm sex-
Sporophyte (diploid stage) is dominant
In flower, pollen produced in anther (tip of stamen) and egg in ovary (base of
pistil)
Stamen-produces sperm
Pistil-produces egg
Pollen spreads between plants mostly by animals
Pollen grain adheres to stigma of pistil and pollen grows into ovary
Pollen tube grows into ovary and releases two sperm cells
Pollen tube grows into ovary and releases two sperm cells
Double fertilization
One sperm cell unites with the egg cell to form the diploid zygote
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